* Merged the `fast-eval' branch.

112 files changed, 3170 insertions, 3835 deletions

diff --git a/configure.ac b/configure.ac
index 4c92bcb5c..8d3f308d7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -203,23 +203,6 @@ AC_ARG_WITH(store-dir, AC_HELP_STRING([--with-store-dir=PATH],
   storedir=$withval, storedir='/nix/store')
 AC_SUBST(storedir)
 
-AC_ARG_WITH(aterm, AC_HELP_STRING([--with-aterm=PATH],
-  [prefix of CWI ATerm library]),
-  aterm=$withval, aterm=)
-AM_CONDITIONAL(HAVE_ATERM, test -n "$aterm")
-if test -z "$aterm"; then
-  aterm_lib='-L${top_builddir}/externals/inst-aterm/lib -lATerm'
-  aterm_include='-I${top_builddir}/externals/inst-aterm/include'
-  aterm_bin='${top_builddir}/externals/inst-aterm/bin'
-else
-  aterm_lib="-L$aterm/lib -lATerm"
-  aterm_include="-I$aterm/include"
-  aterm_bin="$aterm/bin"
-fi
-AC_SUBST(aterm_lib)
-AC_SUBST(aterm_include)
-AC_SUBST(aterm_bin)
-
 AC_ARG_WITH(openssl, AC_HELP_STRING([--with-openssl=PATH],
   [prefix of the OpenSSL library]),
   openssl=$withval, openssl=)
diff --git a/corepkgs/buildenv/builder.pl.in b/corepkgs/buildenv/builder.pl.in
index 4a52df65e..86abe0ca1 100755
--- a/corepkgs/buildenv/builder.pl.in
+++ b/corepkgs/buildenv/builder.pl.in
@@ -168,4 +168,4 @@ while (scalar(keys %postponed) > 0) {
 print STDERR "created $symlinks symlinks in user environment\n";
 
 
-symlink($ENV{"manifest"}, "$out/manifest") or die "cannot create manifest";
+symlink($ENV{"manifest"}, "$out/manifest.nix") or die "cannot create manifest";
diff --git a/doc/manual/installation.xml b/doc/manual/installation.xml
index a1b99ca2e..bc5e21f0d 100644
--- a/doc/manual/installation.xml
+++ b/doc/manual/installation.xml
@@ -96,15 +96,13 @@ ubiquitous 2.5.4a won't.  Note that these are only required if you
 modify the parser or when you are building from the Subversion
 repository.</para>
 
-<para>Nix uses CWI's ATerm library and the bzip2 compressor (including
-the bzip2 library).  These are included in the Nix source
-distribution.  If you build from the Subversion repository, you must
-download them yourself and place them in the
-<filename>externals/</filename> directory.  See
+<para>Nix uses the bzip2 compressor (including the bzip2 library).  It
+is included in the Nix source distribution.  If you build from the
+Subversion repository, you must download it yourself and place it in
+the <filename>externals/</filename> directory.  See
 <filename>externals/Makefile.am</filename> for the precise URLs of
-these packages.  Alternatively, if you already have them installed,
-you can use <command>configure</command>'s
-<option>--with-aterm</option> and <option>--with-bzip2</option>
+this packages.  Alternatively, if you already have it installed, you
+can use <command>configure</command>'s <option>--with-bzip2</option>
 options to point to their respective locations.</para>
 
 </section>
diff --git a/externals/Makefile.am b/externals/Makefile.am
index c9bc05d71..63150b1f5 100644
--- a/externals/Makefile.am
+++ b/externals/Makefile.am
@@ -1,38 +1,3 @@
-# CWI ATerm
-
-ATERM = aterm-2.5
-
-$(ATERM).tar.gz:
-	@echo "Nix requires the CWI ATerm library to build."
-	@echo "Please download version 2.5 from"
-	@echo "  http://nixos.org/tarballs/aterm-2.5.tar.gz"
-	@echo "and place it in the externals/ directory."
-	false
-
-$(ATERM): $(ATERM).tar.gz
-	gzip -d < $(srcdir)/$(ATERM).tar.gz | tar xvf -
-	patch -d $(ATERM) -p1 < ./max-long.patch
-	patch -d $(ATERM) -p1 < ./sizeof.patch
-
-have-aterm:
-	$(MAKE) $(ATERM)
-	touch have-aterm
-
-if HAVE_ATERM
-build-aterm:
-else
-build-aterm: have-aterm
-	(pfx=`pwd` && \
-	cd $(ATERM) && \
-	CC="$(CC)" ./configure --prefix=$$pfx/inst-aterm \
-	  --disable-shared --enable-static && \
-	$(MAKE) && \
-	$(MAKE) check && \
-	$(MAKE) install)
-	touch build-aterm
-endif
-
-
 # bzip2
 
 BZIP2 = bzip2-1.0.5
@@ -67,10 +32,10 @@ install:
 endif
 
 
-all: build-aterm build-bzip2
+all: build-bzip2
 
-EXTRA_DIST = $(ATERM).tar.gz $(BZIP2).tar.gz max-long.patch sizeof.patch
+EXTRA_DIST = $(BZIP2).tar.gz
 
 ext-clean:
-	$(RM) -f have-aterm build-aterm have-bzip2 build-bzip2
-	$(RM) -rf $(ATERM) $(BZIP2)
+	$(RM) -f have-bzip2 build-bzip2
+	$(RM) -rf $(BZIP2)
diff --git a/externals/max-long.patch b/externals/max-long.patch
deleted file mode 100644
index a2f260b97..000000000
--- a/externals/max-long.patch
+++ /dev/null
@@ -1,77 +0,0 @@
-diff -rc aterm-2.8-orig/aterm/hash.c aterm-2.8/aterm/hash.c
-*** aterm-2.8-orig/aterm/hash.c	2008-11-10 13:54:22.000000000 +0100
---- aterm-2.8/aterm/hash.c	2009-01-27 18:14:14.000000000 +0100
-***************
-*** 93,146 ****
-  }
-  
-  /*}}}  */
-- /*{{{  static long calc_long_max() */
-- static long calc_long_max()
-- {
--   long try_long_max;
--   long long_max;
--   long delta;
-- 
--   try_long_max = 1;
--   do {
--     long_max = try_long_max;
--     try_long_max = long_max * 2;
--   } while (try_long_max > 0);
-- 
--   delta = long_max;
--   while (delta > 1) {
--     while (long_max + delta < 0) {
--       delta /= 2;
--     }
--     long_max += delta;
--   }
-- 
--   return long_max;
-- 
-- }
-- /*}}}  */
-  /*{{{  static long calculateNewSize(sizeMinus1, nrdel, nrentries) */
-  
-  static long calculateNewSize
-  (long sizeMinus1, long nr_deletions, long nr_entries)
-  { 
-- 
--   /* Hack: LONG_MAX (limits.h) is often unreliable, we need to find
--    * out the maximum possible value of a signed long dynamically.
--    */
--   static long st_long_max = 0;
-- 
--   /* the resulting length has the form 2^k-1 */
-- 
-    if (nr_deletions >= nr_entries/2) { 
-      return sizeMinus1;
-    }
-  
-!   if (st_long_max == 0) {
-!     st_long_max = calc_long_max();
-!   }
-! 
-!   if (sizeMinus1 > st_long_max / 2) {
-!     return st_long_max-1;
-    }
-  
-    return (2*sizeMinus1)+1;
---- 93,109 ----
-  }
-  
-  /*}}}  */
-  /*{{{  static long calculateNewSize(sizeMinus1, nrdel, nrentries) */
-  
-  static long calculateNewSize
-  (long sizeMinus1, long nr_deletions, long nr_entries)
-  { 
-    if (nr_deletions >= nr_entries/2) { 
-      return sizeMinus1;
-    }
-  
-!   if (sizeMinus1 > LONG_MAX / 2) {
-!     return LONG_MAX-1;
-    }
-  
-    return (2*sizeMinus1)+1;
diff --git a/externals/sizeof.patch b/externals/sizeof.patch
deleted file mode 100644
index 2649cc564..000000000
--- a/externals/sizeof.patch
+++ /dev/null
@@ -1,56 +0,0 @@
-diff -rc -x '*~' aterm-2.5-orig/aterm/aterm.c aterm-2.5/aterm/aterm.c
-*** aterm-2.5-orig/aterm/aterm.c	2007-02-27 23:41:31.000000000 +0100
---- aterm-2.5/aterm/aterm.c	2010-02-23 15:10:38.000000000 +0100
-***************
-*** 150,155 ****
---- 150,157 ----
-    if (initialized)
-      return;
-  
-+   assert(sizeof(long) == sizeof(void *));
-+ 
-    /*{{{  Handle arguments */
-  
-    for (lcv=1; lcv < argc; lcv++) {
-diff -rc -x '*~' aterm-2.5-orig/aterm/encoding.h aterm-2.5/aterm/encoding.h
-*** aterm-2.5-orig/aterm/encoding.h	2007-02-27 23:41:31.000000000 +0100
---- aterm-2.5/aterm/encoding.h	2010-02-23 15:36:05.000000000 +0100
-***************
-*** 10,24 ****
-  {
-  #endif/* __cplusplus */
-  
-! #if SIZEOF_LONG > 4
-! #define AT_64BIT
-  #endif
-  
-! #if SIZEOF_LONG != SIZEOF_VOID_P
-! #error Size of long is not the same as the size of a pointer
-  #endif
-  
-! #if SIZEOF_INT > 4
-  #error Size of int is not 32 bits
-  #endif
-  
---- 10,30 ----
-  {
-  #endif/* __cplusplus */
-  
-! #include <limits.h>
-! 
-! #ifndef SIZEOF_LONG
-! #if ULONG_MAX > 4294967295
-! #define SIZEOF_LONG 8
-! #else
-! #define SIZEOF_LONG 4
-! #endif
-  #endif
-  
-! #if SIZEOF_LONG > 4
-! #define AT_64BIT
-  #endif
-  
-! #if UINT_MAX > 4294967295
-  #error Size of int is not 32 bits
-  #endif
-  
diff --git a/release.nix b/release.nix
index e9afe9c9e..3343f8658 100644
--- a/release.nix
+++ b/release.nix
@@ -29,11 +29,8 @@ let
           --with-xml-flags=--nonet
         '';
 
-        # Include the ATerm and Bzip2 tarballs in the distribution.
+        # Include the Bzip2 tarball in the distribution.
         preConfigure = ''
-          stripHash ${aterm.src}
-          cp -pv ${aterm.src} externals/$strippedName
-
           stripHash ${bzip2.src}
           cp -pv ${bzip2.src} externals/$strippedName
 
@@ -77,7 +74,7 @@ let
 
         configureFlags = ''
           --disable-init-state
-          --with-aterm=${aterm} --with-bzip2=${bzip2}
+          --with-bzip2=${bzip2}
         '';
       };
 
@@ -98,7 +95,7 @@ let
 
         configureFlags = ''
           --disable-init-state
-          --with-aterm=${aterm} --with-bzip2=${bzip2}
+          --with-bzip2=${bzip2}
           --enable-static-nix
         '';
       };
@@ -123,7 +120,7 @@ let
 
         configureFlags = ''
           --disable-init-state --disable-shared
-          --with-aterm=${aterm} --with-bzip2=${bzip2}
+          --with-bzip2=${bzip2}
         '';
 
         lcovFilter = ["*/boost/*" "*-tab.*"];
diff --git a/src/Makefile.am b/src/Makefile.am
index 971f7d9d1..ec3632773 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -1,5 +1,3 @@
 SUBDIRS = bin2c boost libutil libstore libmain nix-store nix-hash \
  libexpr nix-instantiate nix-env nix-worker nix-setuid-helper \
  nix-log2xml bsdiff-4.3
-
-EXTRA_DIST = aterm-helper.pl
diff --git a/src/aterm-helper.pl b/src/aterm-helper.pl
deleted file mode 100755
index f1eb77ee8..000000000
--- a/src/aterm-helper.pl
+++ /dev/null
@@ -1,179 +0,0 @@
-#! /usr/bin/perl -w
-
-# This program generates C/C++ code for efficiently manipulating
-# ATerms.  It generates functions to build and match ATerms according
-# to a set of constructor definitions defined in a file read from
-# standard input.  A constructor is defined by a line with the
-# following format:
-#
-#   SYM | ARGS | TYPE | FUN?
-#
-# where SYM is the name of the constructor, ARGS is a
-# whitespace-separated list of argument types, TYPE is the type of the
-# resulting ATerm (which should be `ATerm' or a type synonym for
-# `ATerm'), and the optional FUN is used to construct the names of the
-# build and match functions (it defaults to SYM; overriding it is
-# useful if there are overloaded constructors, e.g., with different
-# arities).  Note that SYM may be empty.
-#
-# A line of the form
-#
-#   VAR = EXPR
-#
-# causes a ATerm variable to be generated that is initialised to the
-# value EXPR.
-#
-# Finally, a line of the form
-#
-#   init NAME
-#
-# causes the initialisation function to be called `NAME'.  This
-# function must be called before any of the build/match functions or
-# the generated variables are used.
-
-die if scalar @ARGV != 2;
-
-my $syms = "";
-my $init = "";
-my $initFun = "init";
-
-open HEADER, ">$ARGV[0]";
-open IMPL, ">$ARGV[1]";
-
-print HEADER "#include <aterm2.h>\n";
-print HEADER "#ifdef __cplusplus\n";
-print HEADER "namespace nix {\n";
-print HEADER "#endif\n\n\n";
-print IMPL "namespace nix {\n";
-
-while (<STDIN>) {
-    s/\#.*//;
-    next if (/^\s*$/);
-    
-    if (/^\s*(\w*)\s*\|([^\|]*)\|\s*(\w+)\s*\|\s*(\w+)?/) {
-        my $const = $1;
-        my @types = split ' ', $2;
-        my $result = $3;
-        my $funname = $4;
-        $funname = $const unless defined $funname;
-
-        my $formals = "";
-        my $formals2 = "";
-        my $args = "";
-        my $unpack = "";
-        my $n = 1;
-        foreach my $type (@types) {
-            my $realType = $type;
-            $args .= ", ";
-            if ($type eq "string") {
-#                $args .= "(ATerm) ATmakeAppl0(ATmakeAFun((char *) e$n, 0, ATtrue))";
-#                $type = "const char *";
-                $type = "ATerm";
-                $args .= "e$n";
-                # !!! in the matcher, we should check that the
-                # argument is a string (i.e., a nullary application).
-            } elsif ($type eq "int") {
-                $args .= "(ATerm) ATmakeInt(e$n)";
-            } elsif ($type eq "ATermList" || $type eq "ATermBlob") {
-                $args .= "(ATerm) e$n";
-            } else {
-                $args .= "e$n";
-            }
-            $formals .= ", " if $formals ne "";
-            $formals .= "$type e$n";
-            $formals2 .= ", ";
-            $formals2 .= "$type & e$n";
-            my $m = $n - 1;
-            # !!! more checks here
-            if ($type eq "int") {
-                $unpack .= "    e$n = ATgetInt((ATermInt) ATgetArgument(e, $m));\n";
-            } elsif ($type eq "ATermList") {
-                $unpack .= "    e$n = (ATermList) ATgetArgument(e, $m);\n";
-            } elsif ($type eq "ATermBlob") {
-                $unpack .= "    e$n = (ATermBlob) ATgetArgument(e, $m);\n";
-            } elsif ($realType eq "string") {
-                $unpack .= "    e$n = ATgetArgument(e, $m);\n";
-                $unpack .= "    if (ATgetType(e$n) != AT_APPL) return false;\n";
-            } else {
-                $unpack .= "    e$n = ATgetArgument(e, $m);\n";
-            }
-            $n++;
-        }
-
-        my $arity = scalar @types;
-
-        print HEADER "extern AFun sym$funname;\n\n";
-        
-        print IMPL "AFun sym$funname = 0;\n";
-        
-        if ($arity == 0) {
-            print HEADER "extern ATerm const$funname;\n\n";
-            print IMPL "ATerm const$funname = 0;\n";
-        }
-        
-        print HEADER "static inline $result make$funname($formals) __attribute__ ((pure, nothrow));\n";
-        print HEADER "static inline $result make$funname($formals) {\n";
-        if ($arity == 0) {
-            print HEADER "    return const$funname;\n";
-        }
-        elsif ($arity <= 6) {
-            print HEADER "    return (ATerm) ATmakeAppl$arity(sym$funname$args);\n";
-        } else {
-            $args =~ s/^,//;
-            print HEADER "    ATerm array[$arity] = {$args};\n";
-            print HEADER "    return (ATerm) ATmakeApplArray(sym$funname, array);\n";
-        }
-        print HEADER "}\n\n";
-
-        print HEADER "#ifdef __cplusplus\n";
-        print HEADER "static inline bool match$funname(ATerm e$formals2) {\n";
-        print HEADER "    if (ATgetType(e) != AT_APPL || (AFun) ATgetAFun(e) != sym$funname) return false;\n";
-        print HEADER "$unpack";
-        print HEADER "    return true;\n";
-        print HEADER "}\n";
-        print HEADER "#endif\n\n\n";
-
-        $init .= "    sym$funname = ATmakeAFun(\"$const\", $arity, ATfalse);\n";
-        $init .= "    ATprotectAFun(sym$funname);\n";
-        if ($arity == 0) {
-            $init .= "    const$funname = (ATerm) ATmakeAppl0(sym$funname);\n";
-            $init .= "    ATprotect(&const$funname);\n";
-        }
-    }
-
-    elsif (/^\s*(\w+)\s*=\s*(.*)$/) {
-        my $name = $1;
-        my $value = $2;
-        print HEADER "extern ATerm $name;\n";
-        print IMPL "ATerm $name = 0;\n";
-        $init .= "    $name = $value;\n"; 
-        $init .= "    ATprotect(&$name);\n";
-   }
-
-    elsif (/^\s*init\s+(\w+)\s*$/) {
-        $initFun = $1;
-    }
-
-    else {
-        die "bad line: `$_'";
-    }
-}
-
-print HEADER "void $initFun();\n\n";
-
-print HEADER "static inline const char * aterm2String(ATerm t) {\n";
-print HEADER "    return (const char *) ATgetName(ATgetAFun(t));\n";
-print HEADER "}\n\n";
-
-print IMPL "\n";
-print IMPL "void $initFun() {\n";
-print IMPL "$init";
-print IMPL "}\n";
-
-print HEADER "#ifdef __cplusplus\n";
-print HEADER "}\n";
-print HEADER "#endif\n\n\n";
-print IMPL "}\n";
-
-close HEADER;
-close IMPL;
diff --git a/src/libexpr/Makefile.am b/src/libexpr/Makefile.am
index e16600fbf..e7228e183 100644
--- a/src/libexpr/Makefile.am
+++ b/src/libexpr/Makefile.am
@@ -2,27 +2,25 @@ pkglib_LTLIBRARIES = libexpr.la
 
 libexpr_la_SOURCES = \
  nixexpr.cc eval.cc primops.cc lexer-tab.cc parser-tab.cc \
- get-drvs.cc attr-path.cc expr-to-xml.cc common-opts.cc \
+ get-drvs.cc attr-path.cc value-to-xml.cc common-opts.cc \
  names.cc
 
 pkginclude_HEADERS = \
  nixexpr.hh eval.hh parser.hh lexer-tab.hh parser-tab.hh \
- get-drvs.hh attr-path.hh expr-to-xml.hh common-opts.hh \
- names.hh nixexpr-ast.hh
+ get-drvs.hh attr-path.hh value-to-xml.hh common-opts.hh \
+ names.hh symbol-table.hh
 
 libexpr_la_LIBADD = ../libutil/libutil.la ../libstore/libstore.la \
  ../boost/format/libformat.la
 
-BUILT_SOURCES = nixexpr-ast.cc nixexpr-ast.hh \
+BUILT_SOURCES = \
  parser-tab.hh lexer-tab.hh parser-tab.cc lexer-tab.cc
 
-EXTRA_DIST = lexer.l parser.y nixexpr-ast.def nixexpr-ast.cc
+EXTRA_DIST = lexer.l parser.y
 
 AM_CXXFLAGS = \
- -I$(srcdir)/.. ${aterm_include} \
+ -I$(srcdir)/.. \
  -I$(srcdir)/../libutil -I$(srcdir)/../libstore
-AM_CFLAGS = \
- ${aterm_include}
 
 
 # Parser generation.
@@ -34,15 +32,6 @@ lexer-tab.cc lexer-tab.hh: lexer.l
 	$(flex) --outfile lexer-tab.cc --header-file=lexer-tab.hh $(srcdir)/lexer.l 
 
 
-# ATerm helper function generation.
-
-nixexpr-ast.cc nixexpr-ast.hh: ../aterm-helper.pl nixexpr-ast.def
-	$(perl) $(srcdir)/../aterm-helper.pl nixexpr-ast.hh nixexpr-ast.cc < $(srcdir)/nixexpr-ast.def
-
-
-CLEANFILES =
-
-
 # SDF stuff (not built by default).
 nix.tbl: nix.sdf
 	sdf2table -m Nix -s -i nix.sdf -o nix.tbl
diff --git a/src/libexpr/attr-path.cc b/src/libexpr/attr-path.cc
index e8e4c050c..0660ba1c1 100644
--- a/src/libexpr/attr-path.cc
+++ b/src/libexpr/attr-path.cc
@@ -1,23 +1,12 @@
 #include "attr-path.hh"
-#include "nixexpr-ast.hh"
 #include "util.hh"
 
 
 namespace nix {
 
 
-bool isAttrs(EvalState & state, Expr e, ATermMap & attrs)
-{
-    e = evalExpr(state, e);
-    ATermList dummy;
-    if (!matchAttrs(e, dummy)) return false;
-    queryAllAttrs(e, attrs, false);
-    return true;
-}
-
-
-Expr findAlongAttrPath(EvalState & state, const string & attrPath,
-    const ATermMap & autoArgs, Expr e)
+void findAlongAttrPath(EvalState & state, const string & attrPath,
+    const Bindings & autoArgs, Expr * e, Value & v)
 {
     Strings tokens = tokenizeString(attrPath, ".");
 
@@ -25,8 +14,10 @@ Expr findAlongAttrPath(EvalState & state, const string & attrPath,
         Error(format("attribute selection path `%1%' does not match expression") % attrPath);
 
     string curPath;
+
+    state.mkThunk_(v, e);
     
-    for (Strings::iterator i = tokens.begin(); i != tokens.end(); ++i) {
+    foreach (Strings::iterator, i, tokens) {
 
         if (!curPath.empty()) curPath += ".";
         curPath += *i;
@@ -38,7 +29,10 @@ Expr findAlongAttrPath(EvalState & state, const string & attrPath,
         if (string2Int(attr, attrIndex)) apType = apIndex;
 
         /* Evaluate the expression. */
-        e = evalExpr(state, autoCallFunction(evalExpr(state, e), autoArgs));
+        Value vTmp;
+        state.autoCallFunction(autoArgs, v, vTmp);
+        v = vTmp;
+        state.forceValue(v);
 
         /* It should evaluate to either an attribute set or an
            expression, according to what is specified in the
@@ -46,36 +40,31 @@ Expr findAlongAttrPath(EvalState & state, const string & attrPath,
 
         if (apType == apAttr) {
 
-            ATermMap attrs;
-
-            if (!isAttrs(state, e, attrs))
+            if (v.type != tAttrs)
                 throw TypeError(
                     format("the expression selected by the selection path `%1%' should be an attribute set but is %2%")
-                    % curPath % showType(e));
-                
-            e = attrs.get(toATerm(attr));
-            if (!e)
-                throw Error(format("attribute `%1%' in selection path `%2%' not found") % attr % curPath);
+                    % curPath % showType(v));
 
+            Bindings::iterator a = v.attrs->find(state.symbols.create(attr));
+            if (a == v.attrs->end())
+                throw Error(format("attribute `%1%' in selection path `%2%' not found") % attr % curPath);
+            v = a->second.value;
         }
 
         else if (apType == apIndex) {
 
-            ATermList es;
-            if (!matchList(e, es))
+            if (v.type != tList)
                 throw TypeError(
                     format("the expression selected by the selection path `%1%' should be a list but is %2%")
-                    % curPath % showType(e));
+                    % curPath % showType(v));
 
-            e = ATelementAt(es, attrIndex);
-            if (!e)
-                throw Error(format("list index %1% in selection path `%2%' not found") % attrIndex % curPath);
-            
+            if (attrIndex >= v.list.length)
+                throw Error(format("list index %1% in selection path `%2%' is out of range") % attrIndex % curPath);
+
+            v = *v.list.elems[attrIndex];
         }
         
     }
-    
-    return e;
 }
 
  
diff --git a/src/libexpr/attr-path.hh b/src/libexpr/attr-path.hh
index 7abaa83a0..33587e5ed 100644
--- a/src/libexpr/attr-path.hh
+++ b/src/libexpr/attr-path.hh
@@ -10,8 +10,8 @@
 namespace nix {
 
     
-Expr findAlongAttrPath(EvalState & state, const string & attrPath,
-    const ATermMap & autoArgs, Expr e);
+void findAlongAttrPath(EvalState & state, const string & attrPath,
+    const Bindings & autoArgs, Expr * e, Value & v);
 
     
 }
diff --git a/src/libexpr/common-opts.cc b/src/libexpr/common-opts.cc
index 9e3f8f961..5a4856568 100644
--- a/src/libexpr/common-opts.cc
+++ b/src/libexpr/common-opts.cc
@@ -9,7 +9,7 @@ namespace nix {
 
 bool parseOptionArg(const string & arg, Strings::iterator & i,
     const Strings::iterator & argsEnd, EvalState & state,
-    ATermMap & autoArgs)
+    Bindings & autoArgs)
 {
     if (arg != "--arg" && arg != "--argstr") return false;
 
@@ -19,11 +19,13 @@ bool parseOptionArg(const string & arg, Strings::iterator & i,
     string name = *i++;
     if (i == argsEnd) throw error;
     string value = *i++;
-    
-    Expr e = arg == "--arg"
-        ? parseExprFromString(state, value, absPath("."))
-        : makeStr(value);
-    autoArgs.set(toATerm(name), e);
+
+    Value & v(autoArgs[state.symbols.create(name)].value);
+
+    if (arg == "--arg")
+        state.mkThunk_( v, parseExprFromString(state, value, absPath(".")));
+    else
+        mkString(v, value);
     
     return true;
 }
diff --git a/src/libexpr/common-opts.hh b/src/libexpr/common-opts.hh
index fb9659cdc..80298ce55 100644
--- a/src/libexpr/common-opts.hh
+++ b/src/libexpr/common-opts.hh
@@ -9,7 +9,7 @@ namespace nix {
 /* Some common option parsing between nix-env and nix-instantiate. */
 bool parseOptionArg(const string & arg, Strings::iterator & i,
     const Strings::iterator & argsEnd, EvalState & state,
-    ATermMap & autoArgs);
+    Bindings & autoArgs);
     
 }
 
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index cd9c64594..26739faf6 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -4,9 +4,10 @@
 #include "util.hh"
 #include "store-api.hh"
 #include "derivations.hh"
-#include "nixexpr-ast.hh"
 #include "globals.hh"
 
+#include <cstring>
+
 
 #define LocalNoInline(f) static f __attribute__((noinline)); f
 #define LocalNoInlineNoReturn(f) static f __attribute__((noinline, noreturn)); f
@@ -15,23 +16,139 @@
 namespace nix {
     
 
-EvalState::EvalState()
-    : normalForms(32768), primOps(128)
+std::ostream & operator << (std::ostream & str, Value & v)
 {
-    nrEvaluated = nrCached = 0;
+    switch (v.type) {
+    case tInt:
+        str << v.integer;
+        break;
+    case tBool:
+        str << (v.boolean ? "true" : "false");
+        break;
+    case tString:
+        str << "\"";
+        for (const char * i = v.string.s; *i; i++)
+            if (*i == '\"' || *i == '\\') str << "\\" << *i;
+            else if (*i == '\n') str << "\\n";
+            else if (*i == '\r') str << "\\r";
+            else if (*i == '\t') str << "\\t";
+            else str << *i;
+        str << "\"";
+        break;
+    case tPath:
+        str << v.path; // !!! escaping?
+        break;
+    case tNull:
+        str << "true";
+        break;
+    case tAttrs: {
+        str << "{ ";
+        typedef std::map<string, Value *> Sorted;
+        Sorted sorted;
+        foreach (Bindings::iterator, i, *v.attrs)
+            sorted[i->first] = &i->second.value;
+        foreach (Sorted::iterator, i, sorted)
+            str << i->first << " = " << *i->second << "; ";
+        str << "}";
+        break;
+    }
+    case tList:
+        str << "[ ";
+        for (unsigned int n = 0; n < v.list.length; ++n)
+            str << *v.list.elems[n] << " ";
+        str << "]";
+        break;
+    case tThunk:
+    case tCopy:
+        str << "<CODE>";
+        break;
+    case tLambda:
+        str << "<LAMBDA>";
+        break;
+    case tPrimOp:
+        str << "<PRIMOP>";
+        break;
+    case tPrimOpApp:
+        str << "<PRIMOP-APP>";
+        break;
+    default:
+        throw Error("invalid value");
+    }
+    return str;
+}
 
-    initNixExprHelpers();
 
-    addPrimOps();
+string showType(const Value & v)
+{
+    switch (v.type) {
+        case tInt: return "an integer";
+        case tBool: return "a boolean";
+        case tString: return "a string";
+        case tPath: return "a path";
+        case tNull: return "null";
+        case tAttrs: return "an attribute set";
+        case tList: return "a list";
+        case tThunk: return "a thunk";
+        case tApp: return "a function application";
+        case tLambda: return "a function";
+        case tCopy: return "a copy";
+        case tBlackhole: return "a black hole";
+        case tPrimOp: return "a built-in function";
+        case tPrimOpApp: return "a partially applied built-in function";
+    }
+    abort();
+}
 
+
+EvalState::EvalState()
+    : sWith(symbols.create("<with>"))
+    , sOutPath(symbols.create("outPath"))
+    , sDrvPath(symbols.create("drvPath"))
+    , sType(symbols.create("type"))
+    , sMeta(symbols.create("meta"))
+    , sName(symbols.create("name"))
+    , sSystem(symbols.create("system"))
+    , baseEnv(allocEnv(128))
+    , baseEnvDispl(0)
+    , staticBaseEnv(false, 0)
+{
+    nrEnvs = nrValuesInEnvs = nrValues = nrListElems = 0;
+    nrEvaluated = recursionDepth = maxRecursionDepth = 0;
+    deepestStack = (char *) -1;
+
+    createBaseEnv();
+    
     allowUnsafeEquality = getEnv("NIX_NO_UNSAFE_EQ", "") == "";
 }
 
 
+EvalState::~EvalState()
+{
+    assert(recursionDepth == 0);
+}
+
+
+void EvalState::addConstant(const string & name, Value & v)
+{
+    staticBaseEnv.vars[symbols.create(name)] = baseEnvDispl;
+    baseEnv.values[baseEnvDispl++] = v;
+    string name2 = string(name, 0, 2) == "__" ? string(name, 2) : name;
+    (*baseEnv.values[0].attrs)[symbols.create(name2)].value = v;
+}
+
+
 void EvalState::addPrimOp(const string & name,
     unsigned int arity, PrimOp primOp)
 {
-    primOps.set(toATerm(name), makePrimOpDef(arity, ATmakeBlob(0, (void *) primOp)));
+    Value v;
+    string name2 = string(name, 0, 2) == "__" ? string(name, 2) : name;
+    v.type = tPrimOp;
+    v.primOp.arity = arity;
+    v.primOp.fun = primOp;
+    v.primOp.name = strdup(name2.c_str());
+    staticBaseEnv.vars[symbols.create(name)] = baseEnvDispl;
+    baseEnv.values[baseEnvDispl++] = v;
+    (*baseEnv.values[0].attrs)[symbols.create(name2)].value = v;
 }
 
 
@@ -50,6 +167,11 @@ LocalNoInlineNoReturn(void throwEvalError(const char * s, const string & s2))
     throw EvalError(format(s) % s2);
 }
 
+LocalNoInlineNoReturn(void throwEvalError(const char * s, const string & s2, const string & s3))
+{
+    throw EvalError(format(s) % s2 % s3);
+}
+
 LocalNoInlineNoReturn(void throwTypeError(const char * s))
 {
     throw TypeError(s);
@@ -60,9 +182,19 @@ LocalNoInlineNoReturn(void throwTypeError(const char * s, const string & s2))
     throw TypeError(format(s) % s2);
 }
 
-LocalNoInline(void addErrorPrefix(Error & e, const char * s))
+LocalNoInlineNoReturn(void throwTypeError(const char * s, const Pos & pos, const string & s2))
+{
+    throw TypeError(format(s) % pos % s2);
+}
+
+LocalNoInlineNoReturn(void throwTypeError(const char * s, const Pos & pos))
+{
+    throw TypeError(format(s) % pos);
+}
+
+LocalNoInlineNoReturn(void throwAssertionError(const char * s, const Pos & pos))
 {
-    e.addPrefix(s);
+    throw AssertionError(format(s) % pos);
 }
 
 LocalNoInline(void addErrorPrefix(Error & e, const char * s, const string & s2))
@@ -70,845 +202,884 @@ LocalNoInline(void addErrorPrefix(Error & e, const char * s, const string & s2))
     e.addPrefix(format(s) % s2);
 }
 
-LocalNoInline(void addErrorPrefix(Error & e, const char * s, const string & s2, const string & s3))
+LocalNoInline(void addErrorPrefix(Error & e, const char * s, const Pos & pos))
 {
-    e.addPrefix(format(s) % s2 % s3);
+    e.addPrefix(format(s) % pos);
+}
+
+LocalNoInline(void addErrorPrefix(Error & e, const char * s, const string & s2, const Pos & pos))
+{
+    e.addPrefix(format(s) % s2 % pos);
 }
 
 
-/* Pattern-match `pat' against `arg'.  The result is a set of
-   substitutions (`subs') and a set of recursive substitutions
-   (`subsRecursive').  The latter can refer to the variables bound by
-   both `subs' and `subsRecursive'. */
-static void patternMatch(EvalState & state,
-    Pattern pat, Expr arg, ATermMap & subs, ATermMap & subsRecursive)
+void mkString(Value & v, const char * s)
 {
-    ATerm name;
-    ATermList formals;
-    Pattern pat1, pat2;
-    ATermBool ellipsis;
-    
-    if (matchVarPat(pat, name)) 
-        subs.set(name, arg);
+    v.type = tString;
+    v.string.s = strdup(s);
+    v.string.context = 0;
+}
 
-    else if (matchAttrsPat(pat, formals, ellipsis)) {
 
-        arg = evalExpr(state, arg);
+void mkString(Value & v, const string & s, const PathSet & context)
+{
+    mkString(v, s.c_str());
+    if (!context.empty()) {
+        unsigned int n = 0;
+        v.string.context = new const char *[context.size() + 1];
+        foreach (PathSet::const_iterator, i, context) 
+            v.string.context[n++] = strdup(i->c_str());
+        v.string.context[n] = 0;
+    }
+}
 
-        /* Get the actual arguments. */
-        ATermMap attrs;
-        queryAllAttrs(arg, attrs);
-        unsigned int nrAttrs = attrs.size();
 
-        /* For each formal argument, get the actual argument.  If
-           there is no matching actual argument but the formal
-           argument has a default, use the default. */
-        unsigned int attrsUsed = 0;
-        for (ATermIterator i(formals); i; ++i) {
-            Expr name, def;
-            DefaultValue def2;
-            if (!matchFormal(*i, name, def2)) abort(); /* can't happen */
-
-            Expr value = attrs[name];
-
-            if (value == 0) {
-                if (!matchDefaultValue(def2, def)) def = 0;
-                if (def == 0) throw TypeError(format("the argument named `%1%' required by the function is missing")
-                    % aterm2String(name));
-                subsRecursive.set(name, def);
-            } else {
-                attrsUsed++;
-                attrs.remove(name);
-                subs.set(name, value);
-            }
+void mkPath(Value & v, const char * s)
+{
+    v.type = tPath;
+    v.path = strdup(s);
+}
+
 
+Value * EvalState::lookupVar(Env * env, const VarRef & var)
+{
+    for (unsigned int l = var.level; l; --l, env = env->up) ;
+    
+    if (var.fromWith) {
+        while (1) {
+            Bindings::iterator j = env->values[0].attrs->find(var.name);
+            if (j != env->values[0].attrs->end())
+                return &j->second.value;
+            if (env->prevWith == 0)
+                throwEvalError("undefined variable `%1%'", var.name);
+            for (unsigned int l = env->prevWith; l; --l, env = env->up) ;
         }
+    } else
+        return &env->values[var.displ];
+}
 
-        /* Check that each actual argument is listed as a formal
-           argument (unless the attribute match specifies a `...'). */
-        if (ellipsis == eFalse && attrsUsed != nrAttrs)
-            throw TypeError(format("the function does not expect an argument named `%1%'")
-                % aterm2String(attrs.begin()->key));
-    }
 
-    else if (matchAtPat(pat, pat1, pat2)) {
-        patternMatch(state, pat1, arg, subs, subsRecursive);
-        patternMatch(state, pat2, arg, subs, subsRecursive);
-    }
+Value * EvalState::allocValues(unsigned int count)
+{
+    nrValues += count;
+    return new Value[count]; // !!! check destructor
+}
+
 
-    else abort();
+Env & EvalState::allocEnv(unsigned int size)
+{
+    nrEnvs++;
+    nrValuesInEnvs += size;
+    Env * env = (Env *) malloc(sizeof(Env) + size * sizeof(Value));
+    return *env;
 }
 
 
-/* Substitute an argument set into the body of a function. */
-static Expr substArgs(EvalState & state,
-    Expr body, Pattern pat, Expr arg)
+void EvalState::mkList(Value & v, unsigned int length)
 {
-    ATermMap subs(16), subsRecursive(16);
-    
-    patternMatch(state, pat, arg, subs, subsRecursive);
-
-    /* If we used any default values, make a recursive attribute set
-       out of the (argument-name, value) tuples.  This is so that we
-       can support default values that refer to each other, e.g.  ({x,
-       y ? x + x}: y) {x = "foo";} evaluates to "foofoo". */
-    if (subsRecursive.size() != 0) {
-        ATermList recAttrs = ATempty;
-        foreach (ATermMap::const_iterator, i, subs)
-            recAttrs = ATinsert(recAttrs, makeBind(i->key, i->value, makeNoPos()));
-        foreach (ATermMap::const_iterator, i, subsRecursive)
-            recAttrs = ATinsert(recAttrs, makeBind(i->key, i->value, makeNoPos()));
-        Expr rec = makeRec(recAttrs, ATempty);
-        foreach (ATermMap::const_iterator, i, subsRecursive)
-            subs.set(i->key, makeSelect(rec, i->key));
-    }
+    v.type = tList;
+    v.list.length = length;
+    v.list.elems = new Value *[length];
+    nrListElems += length;
+}
+
 
-    return substitute(Substitution(0, &subs), body);
+void EvalState::mkAttrs(Value & v)
+{
+    v.type = tAttrs;
+    v.attrs = new Bindings;
 }
 
 
-/* Transform a mutually recursive set into a non-recursive set.  Each
-   attribute is transformed into an expression that has all references
-   to attributes substituted with selection expressions on the
-   original set.  E.g., e = `rec {x = f x y; y = x;}' becomes `{x = f
-   (e.x) (e.y); y = e.x;}'. */
-LocalNoInline(ATerm expandRec(EvalState & state, ATerm e, ATermList rbnds, ATermList nrbnds))
+void EvalState::mkThunk_(Value & v, Expr * expr)
 {
-    ATerm name;
-    Expr e2;
-    Pos pos;
-    Expr eOverrides = 0;
+    mkThunk(v, baseEnv, expr);
+}
 
-    /* Create the substitution list. */
-    ATermMap subs(ATgetLength(rbnds) + ATgetLength(nrbnds));
-    for (ATermIterator i(rbnds); i; ++i) {
-        if (!matchBind(*i, name, e2, pos)) abort(); /* can't happen */
-        subs.set(name, makeSelect(e, name));
-    }
-    for (ATermIterator i(nrbnds); i; ++i) {
-        if (!matchBind(*i, name, e2, pos)) abort(); /* can't happen */
-        if (name == sOverrides) eOverrides = e2;
-        subs.set(name, e2);
-    }
 
-    /* If the rec contains an attribute called `__overrides', then
-       evaluate it, and add the attributes in that set to the rec.
-       This allows overriding of recursive attributes, which is
-       otherwise not possible.  (You can use the // operator to
-       replace an attribute, but other attributes in the rec will
-       still reference the original value, because that value has been
-       substituted into the bodies of the other attributes.  Hence we
-       need __overrides.) */
-    ATermMap overrides;
-    if (eOverrides) {
-        eOverrides = evalExpr(state, eOverrides);
-        queryAllAttrs(eOverrides, overrides, false);
-        foreach (ATermMap::const_iterator, i, overrides)
-            subs.set(i->key, i->value);
+void EvalState::cloneAttrs(Value & src, Value & dst)
+{
+    mkAttrs(dst);
+    foreach (Bindings::iterator, i, *src.attrs) {
+        Attr & a = (*dst.attrs)[i->first];
+        mkCopy(a.value, i->second.value);
+        a.pos = i->second.pos;
     }
+}
 
-    Substitution subs_(0, &subs);
 
-    /* Create the non-recursive set. */
-    ATermMap as(ATgetLength(rbnds) + ATgetLength(nrbnds));
-    for (ATermIterator i(rbnds); i; ++i) {
-        if (!matchBind(*i, name, e2, pos)) abort(); /* can't happen */
-        as.set(name, makeAttrRHS(substitute(subs_, e2), pos));
-    }
+void EvalState::evalFile(const Path & path, Value & v)
+{
+    startNest(nest, lvlTalkative, format("evaluating file `%1%'") % path);
 
-    if (eOverrides)
-        foreach (ATermMap::const_iterator, i, overrides)
-            as.set(i->key, makeAttrRHS(i->value, makeNoPos()));
+    Expr * e = parseTrees[path];
 
-    /* Copy the non-recursive bindings.  !!! inefficient */
-    for (ATermIterator i(nrbnds); i; ++i) {
-        if (!matchBind(*i, name, e2, pos)) abort(); /* can't happen */
-        as.set(name, makeAttrRHS(e2, pos));
+    if (!e) {
+        e = parseExprFromFile(*this, path);
+        parseTrees[path] = e;
+    }
+    
+    try {
+        eval(e, v);
+    } catch (Error & e) {
+        addErrorPrefix(e, "while evaluating the file `%1%':\n", path);
+        throw;
     }
-
-    return makeAttrs(as);
 }
 
 
-LocalNoInline(Expr updateAttrs(Expr e1, Expr e2))
+struct RecursionCounter
 {
-    /* Note: e1 and e2 should be in normal form. */
+    EvalState & state;
+    RecursionCounter(EvalState & state) : state(state)
+    {
+        state.recursionDepth++;
+        if (state.recursionDepth > state.maxRecursionDepth)
+            state.maxRecursionDepth = state.recursionDepth;
+    }
+    ~RecursionCounter()
+    {   
+        state.recursionDepth--;
+    }
+};
 
-    ATermMap attrs;
-    queryAllAttrs(e1, attrs, true);
-    queryAllAttrs(e2, attrs, true);
 
-    return makeAttrs(attrs);
-}
+void EvalState::eval(Env & env, Expr * e, Value & v)
+{
+    /* When changing this function, make sure that you don't cause a
+       (large) increase in stack consumption! */
 
+    /* !!! Disable this eventually. */
+    RecursionCounter r(*this);
+    char x;
+    if (&x < deepestStack) deepestStack = &x;
+    
+    //debug(format("eval: %1%") % *e);
 
-string evalString(EvalState & state, Expr e, PathSet & context)
-{
-    e = evalExpr(state, e);
-    string s;
-    if (!matchStr(e, s, context))
-        throwTypeError("value is %1% while a string was expected", showType(e));
-    return s;
+    checkInterrupt();
+
+    nrEvaluated++;
+
+    e->eval(*this, env, v);
 }
 
 
-string evalStringNoCtx(EvalState & state, Expr e)
+void EvalState::eval(Expr * e, Value & v)
 {
-    PathSet context;
-    string s = evalString(state, e, context);
-    if (!context.empty())
-        throw EvalError(format("the string `%1%' is not allowed to refer to a store path (such as `%2%')")
-            % s % *(context.begin()));
-    return s;
+    eval(baseEnv, e, v);
 }
 
 
-int evalInt(EvalState & state, Expr e)
+bool EvalState::evalBool(Env & env, Expr * e)
 {
-    e = evalExpr(state, e);
-    int i;
-    if (!matchInt(e, i))
-        throwTypeError("value is %1% while an integer was expected", showType(e));
-    return i;
+    Value v;
+    eval(env, e, v);
+    if (v.type != tBool)
+        throwTypeError("value is %1% while a Boolean was expected", showType(v));
+    return v.boolean;
 }
 
 
-bool evalBool(EvalState & state, Expr e)
+void EvalState::evalAttrs(Env & env, Expr * e, Value & v)
 {
-    e = evalExpr(state, e);
-    if (e == eTrue) return true;
-    else if (e == eFalse) return false;
-    else throwTypeError("value is %1% while a boolean was expected", showType(e));
+    eval(env, e, v);
+    if (v.type != tAttrs)
+        throwTypeError("value is %1% while an attribute set was expected", showType(v));
 }
 
 
-ATermList evalList(EvalState & state, Expr e)
+void Expr::eval(EvalState & state, Env & env, Value & v)
 {
-    e = evalExpr(state, e);
-    ATermList list;
-    if (!matchList(e, list))
-        throwTypeError("value is %1% while a list was expected", showType(e));
-    return list;
+    abort();
 }
 
 
-static void flattenList(EvalState & state, Expr e, ATermList & result)
+void ExprInt::eval(EvalState & state, Env & env, Value & v)
 {
-    ATermList es;
-    e = evalExpr(state, e);
-    if (matchList(e, es))
-        for (ATermIterator i(es); i; ++i)
-            flattenList(state, *i, result);
-    else
-        result = ATinsert(result, e);
+    mkInt(v, n);
 }
 
 
-ATermList flattenList(EvalState & state, Expr e)
+void ExprString::eval(EvalState & state, Env & env, Value & v)
 {
-    ATermList result = ATempty;
-    flattenList(state, e, result);
-    return ATreverse(result);
+    mkString(v, s.c_str());
 }
 
 
-string coerceToString(EvalState & state, Expr e, PathSet & context,
-    bool coerceMore, bool copyToStore)
+void ExprPath::eval(EvalState & state, Env & env, Value & v)
 {
-    e = evalExpr(state, e);
+    mkPath(v, s.c_str());
+}
 
-    string s;
 
-    if (matchStr(e, s, context)) return s;
+void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
+{
+    state.mkAttrs(v);
 
-    ATerm s2;
-    if (matchPath(e, s2)) {
-        Path path(canonPath(aterm2String(s2)));
+    if (recursive) {
+        /* Create a new environment that contains the attributes in
+           this `rec'. */
+        Env & env2(state.allocEnv(attrs.size() + inherited.size()));
+        env2.up = &env;
 
-        if (!copyToStore) return path;
+        unsigned int displ = 0;
         
-        if (isDerivation(path))
-            throw EvalError(format("file names are not allowed to end in `%1%'")
-                % drvExtension);
+        /* The recursive attributes are evaluated in the new
+           environment. */
+        foreach (Attrs::iterator, i, attrs) {
+            nix::Attr & a = (*v.attrs)[i->first];
+            mkCopy(a.value, env2.values[displ]);
+            mkThunk(env2.values[displ++], env2, i->second.first);
+            a.pos = &i->second.second;
+        }
 
-        Path dstPath;
-        if (state.srcToStore[path] != "")
-            dstPath = state.srcToStore[path];
-        else {
-            dstPath = readOnlyMode
-                ? computeStorePathForPath(path).first
-                : store->addToStore(path);
-            state.srcToStore[path] = dstPath;
-            printMsg(lvlChatty, format("copied source `%1%' -> `%2%'")
-                % path % dstPath);
+        /* The inherited attributes, on the other hand, are
+           evaluated in the original environment. */
+        foreach (list<Inherited>::iterator, i, inherited) {
+            nix::Attr & a = (*v.attrs)[i->first.name];
+            Value * v2 = state.lookupVar(&env, i->first);
+            mkCopy(a.value, *v2);
+            mkCopy(env2.values[displ++], *v2);
+            a.pos = &i->second;
         }
 
-        context.insert(dstPath);
-        return dstPath;
-    }
-        
-    ATermList es;
-    if (matchAttrs(e, es)) {
-        Expr e2 = queryAttr(e, "outPath");
-        if (!e2) throwTypeError("cannot coerce an attribute set (except a derivation) to a string");
-        return coerceToString(state, e2, context, coerceMore, copyToStore);
     }
 
-    if (coerceMore) {
-
-        /* Note that `false' is represented as an empty string for
-           shell scripting convenience, just like `null'. */
-        if (e == eTrue) return "1";
-        if (e == eFalse) return "";
-        int n;
-        if (matchInt(e, n)) return int2String(n);
-        if (matchNull(e)) return "";
+    else {
+        foreach (Attrs::iterator, i, attrs) {
+            nix::Attr & a = (*v.attrs)[i->first];
+            mkThunk(a.value, env, i->second.first);
+            a.pos = &i->second.second;
+        }
 
-        if (matchList(e, es)) {
-            string result;
-            es = flattenList(state, e);
-            bool first = true;
-            for (ATermIterator i(es); i; ++i) {
-                if (!first) result += " "; else first = false;
-                result += coerceToString(state, *i,
-                    context, coerceMore, copyToStore);
-            }
-            return result;
+        foreach (list<Inherited>::iterator, i, inherited) {
+            nix::Attr & a = (*v.attrs)[i->first.name];
+            mkCopy(a.value, *state.lookupVar(&env, i->first));
+            a.pos = &i->second;
         }
     }
-    
-    throwTypeError("cannot coerce %1% to a string", showType(e));
 }
 
 
-/* Common implementation of `+', ConcatStrings and `~'. */
-static ATerm concatStrings(EvalState & state, ATermVector & args,
-    string separator = "")
+void ExprLet::eval(EvalState & state, Env & env, Value & v)
 {
-    if (args.empty()) return makeStr("", PathSet());
-    
-    PathSet context;
-    std::ostringstream s;
+    /* Create a new environment that contains the attributes in this
+       `let'. */
+    Env & env2(state.allocEnv(attrs->attrs.size() + attrs->inherited.size()));
+    env2.up = &env;
 
-    /* If the first element is a path, then the result will also be a
-       path, we don't copy anything (yet - that's done later, since
-       paths are copied when they are used in a derivation), and none
-       of the strings are allowed to have contexts. */
-    ATerm dummy;
-    args.front() = evalExpr(state, args.front());
-    bool isPath = matchPath(args.front(), dummy);
-
-    for (ATermVector::const_iterator i = args.begin(); i != args.end(); ++i) {
-        if (i != args.begin()) s << separator;
-        s << coerceToString(state, *i, context, false, !isPath);
-    }
+    unsigned int displ = 0;
 
-    if (isPath && !context.empty())
-        throw EvalError(format("a string that refers to a store path cannot be appended to a path, in `%1%'")
-            % s.str());
-    
-    return isPath
-        ? makePath(toATerm(s.str()))
-        : makeStr(s.str(), context);
+    /* The recursive attributes are evaluated in the new
+       environment. */
+    foreach (ExprAttrs::Attrs::iterator, i, attrs->attrs)
+        mkThunk(env2.values[displ++], env2, i->second.first);
+
+    /* The inherited attributes, on the other hand, are evaluated in
+       the original environment. */
+    foreach (list<ExprAttrs::Inherited>::iterator, i, attrs->inherited)
+        mkCopy(env2.values[displ++], *state.lookupVar(&env, i->first));
+
+    state.eval(env2, body, v);
 }
 
 
-Path coerceToPath(EvalState & state, Expr e, PathSet & context)
+void ExprList::eval(EvalState & state, Env & env, Value & v)
 {
-    string path = coerceToString(state, e, context, false, false);
-    if (path == "" || path[0] != '/')
-        throw EvalError(format("string `%1%' doesn't represent an absolute path") % path);
-    return path;
+    state.mkList(v, elems.size());
+    Value * vs = state.allocValues(v.list.length);
+    for (unsigned int n = 0; n < v.list.length; ++n) {
+        v.list.elems[n] = &vs[n];
+        mkThunk(vs[n], env, elems[n]);
+    }
 }
 
 
-Expr autoCallFunction(Expr e, const ATermMap & args)
+void ExprVar::eval(EvalState & state, Env & env, Value & v)
 {
-    Pattern pat;
-    ATerm body, pos;
-    ATermList formals;
-    ATermBool ellipsis;
-    
-    /* !!! this should be more general */
-    if (matchFunction(e, pat, body, pos) && matchAttrsPat(pat, formals, ellipsis)) {
-        ATermMap actualArgs(ATgetLength(formals));
-        
-        for (ATermIterator i(formals); i; ++i) {
-            Expr name, def, value; ATerm def2;
-            if (!matchFormal(*i, name, def2)) abort();
-            if ((value = args.get(name)))
-                actualArgs.set(name, makeAttrRHS(value, makeNoPos()));
-            else if (!matchDefaultValue(def2, def))
-                throw TypeError(format("cannot auto-call a function that has an argument without a default value (`%1%')")
-                    % aterm2String(name));
-        }
-        
-        e = makeCall(e, makeAttrs(actualArgs));
+    Value * v2 = state.lookupVar(&env, info);
+    state.forceValue(*v2);
+    v = *v2;
+}
+
+
+void ExprSelect::eval(EvalState & state, Env & env, Value & v)
+{
+    Value v2;
+    state.evalAttrs(env, e, v2);
+    Bindings::iterator i = v2.attrs->find(name);
+    if (i == v2.attrs->end())
+        throwEvalError("attribute `%1%' missing", name);
+    try {            
+        state.forceValue(i->second.value);
+    } catch (Error & e) {
+        addErrorPrefix(e, "while evaluating the attribute `%1%' at %2%:\n",
+            name, *i->second.pos);
+        throw;
     }
-    
-    return e;
+    v = i->second.value;
 }
 
 
-/* Evaluation of various language constructs.  These have been taken
-   out of evalExpr2 to reduce stack space usage.  (GCC is really dumb
-   about stack space: it just adds up all the local variables and
-   temporaries of every scope into one huge stack frame.  This is
-   really bad for deeply recursive functions.) */
+void ExprOpHasAttr::eval(EvalState & state, Env & env, Value & v)
+{
+    Value vAttrs;
+    state.evalAttrs(env, e, vAttrs);
+    mkBool(v, vAttrs.attrs->find(name) != vAttrs.attrs->end());
+}
 
 
-LocalNoInline(Expr evalVar(EvalState & state, ATerm name))
+void ExprLambda::eval(EvalState & state, Env & env, Value & v)
 {
-    ATerm primOp = state.primOps.get(name);
-    if (!primOp)
-        throw EvalError(format("impossible: undefined variable `%1%'") % aterm2String(name));
-    int arity;
-    ATermBlob fun;
-    if (!matchPrimOpDef(primOp, arity, fun)) abort();
-    if (arity == 0)
-        /* !!! backtrace for primop call */
-        return ((PrimOp) ATgetBlobData(fun)) (state, ATermVector());
-    else
-        return makePrimOp(arity, fun, ATempty);
+    v.type = tLambda;
+    v.lambda.env = &env;
+    v.lambda.fun = this;
 }
 
 
-LocalNoInline(Expr evalCall(EvalState & state, Expr fun, Expr arg))
+void ExprApp::eval(EvalState & state, Env & env, Value & v)
 {
-    Pattern pat;
-    ATerm pos;
-    Expr body;
-        
-    /* Evaluate the left-hand side. */
-    fun = evalExpr(state, fun);
-
-    /* Is it a primop or a function? */
-    int arity;
-    ATermBlob funBlob;
-    ATermList args;
-    if (matchPrimOp(fun, arity, funBlob, args)) {
-        args = ATinsert(args, arg);
-        if (ATgetLength(args) == arity) {
-            /* Put the arguments in a vector in reverse (i.e.,
-               actual) order. */
-            ATermVector args2(arity);
-            for (ATermIterator i(args); i; ++i)
-                args2[--arity] = *i;
-            /* !!! backtrace for primop call */
-            return ((PrimOp) ATgetBlobData(funBlob))
-                (state, args2);
-        } else
-            /* Need more arguments, so propagate the primop. */
-            return makePrimOp(arity, funBlob, args);
-    }
+    Value vFun;
+    state.eval(env, e1, vFun);
+    Value vArg;
+    mkThunk(vArg, env, e2); // !!! should this be on the heap?
+    state.callFunction(vFun, vArg, v);
+}
 
-    else if (matchFunction(fun, pat, body, pos)) {
-        try {
-            return evalExpr(state, substArgs(state, body, pat, arg));
-        } catch (Error & e) {
-            addErrorPrefix(e, "while evaluating the function at %1%:\n",
-                showPos(pos));
-            throw;
+
+void EvalState::callFunction(Value & fun, Value & arg, Value & v)
+{
+    if (fun.type == tPrimOp || fun.type == tPrimOpApp) {
+        unsigned int argsLeft =
+            fun.type == tPrimOp ? fun.primOp.arity : fun.primOpApp.argsLeft;
+        if (argsLeft == 1) {
+            /* We have all the arguments, so call the primop.  First
+               find the primop. */
+            Value * primOp = &fun;
+            while (primOp->type == tPrimOpApp) primOp = primOp->primOpApp.left;
+            assert(primOp->type == tPrimOp);
+            unsigned int arity = primOp->primOp.arity;
+                
+            /* Put all the arguments in an array. */
+            Value * vArgs[arity];
+            unsigned int n = arity - 1;
+            vArgs[n--] = &arg;
+            for (Value * arg = &fun; arg->type == tPrimOpApp; arg = arg->primOpApp.left)
+                vArgs[n--] = arg->primOpApp.right;
+
+            /* And call the primop. */
+            try {
+                primOp->primOp.fun(*this, vArgs, v);
+            } catch (Error & e) {
+                addErrorPrefix(e, "while evaluating the builtin function `%1%':\n", primOp->primOp.name);
+                throw;
+            }
+        } else {
+            Value * v2 = allocValues(2);
+            v2[0] = fun;
+            v2[1] = arg;
+            v.type = tPrimOpApp;
+            v.primOpApp.left = &v2[0];
+            v.primOpApp.right = &v2[1];
+            v.primOpApp.argsLeft = argsLeft - 1;
         }
+        return;
     }
+    
+    if (fun.type != tLambda)
+        throwTypeError("attempt to call something which is neither a function nor a primop (built-in operation) but %1%",
+            showType(fun));
+
+    unsigned int size =
+        (fun.lambda.fun->arg.empty() ? 0 : 1) +
+        (fun.lambda.fun->matchAttrs ? fun.lambda.fun->formals->formals.size() : 0);
+    Env & env2(allocEnv(size));
+    env2.up = fun.lambda.env;
+
+    unsigned int displ = 0;
+
+    if (!fun.lambda.fun->matchAttrs)
+        env2.values[displ++] = arg;
+
+    else {
+        forceAttrs(arg);
         
-    else throwTypeError(
-        "attempt to call something which is neither a function nor a primop (built-in operation) but %1%",
-        showType(fun));
-}
+        if (!fun.lambda.fun->arg.empty())
+            env2.values[displ++] = arg;
 
+        /* For each formal argument, get the actual argument.  If
+           there is no matching actual argument but the formal
+           argument has a default, use the default. */
+        unsigned int attrsUsed = 0;
+        foreach (Formals::Formals_::iterator, i, fun.lambda.fun->formals->formals) {
+            Bindings::iterator j = arg.attrs->find(i->name);
+            if (j == arg.attrs->end()) {
+                if (!i->def) throwTypeError("function at %1% called without required argument `%2%'",
+                    fun.lambda.fun->pos, i->name);   
+                mkThunk(env2.values[displ++], env2, i->def);
+            } else {
+                attrsUsed++;
+                mkCopy(env2.values[displ++], j->second.value);
+            }
+        }
+
+        /* Check that each actual argument is listed as a formal
+           argument (unless the attribute match specifies a `...').
+           TODO: show the names of the expected/unexpected
+           arguments. */
+        if (!fun.lambda.fun->formals->ellipsis && attrsUsed != arg.attrs->size())
+            throwTypeError("function at %1% called with unexpected argument", fun.lambda.fun->pos);
+    }
 
-LocalNoInline(Expr evalSelect(EvalState & state, Expr e, ATerm name))
-{
-    ATerm pos;
-    string s = aterm2String(name);
-    Expr a = queryAttr(evalExpr(state, e), s, pos);
-    if (!a) throwEvalError("attribute `%1%' missing", s);
     try {
-        return evalExpr(state, a);
+        eval(env2, fun.lambda.fun->body, v);
     } catch (Error & e) {
-        addErrorPrefix(e, "while evaluating the attribute `%1%' at %2%:\n",
-            s, showPos(pos));
+        addErrorPrefix(e, "while evaluating the function at %1%:\n", fun.lambda.fun->pos);
         throw;
     }
 }
 
 
-LocalNoInline(Expr evalAssert(EvalState & state, Expr cond, Expr body, ATerm pos))
+void EvalState::autoCallFunction(const Bindings & args, Value & fun, Value & res)
 {
-    if (!evalBool(state, cond))
-        throw AssertionError(format("assertion failed at %1%") % showPos(pos));
-    return evalExpr(state, body);
-}
+    forceValue(fun);
 
+    if (fun.type != tLambda || !fun.lambda.fun->matchAttrs) {
+        res = fun;
+        return;
+    }
 
-LocalNoInline(Expr evalWith(EvalState & state, Expr defs, Expr body, ATerm pos))
-{
-    ATermMap attrs;
-    try {
-        defs = evalExpr(state, defs);
-        queryAllAttrs(defs, attrs);
-    } catch (Error & e) {
-        addErrorPrefix(e, "while evaluating the `with' definitions at %1%:\n",
-            showPos(pos));
-        throw;
+    Value actualArgs;
+    mkAttrs(actualArgs);
+
+    foreach (Formals::Formals_::iterator, i, fun.lambda.fun->formals->formals) {
+        Bindings::const_iterator j = args.find(i->name);
+        if (j != args.end())
+            (*actualArgs.attrs)[i->name] = j->second;
+        else if (!i->def)
+            throwTypeError("cannot auto-call a function that has an argument without a default value (`%1%')", i->name);
     }
-    try {
-        body = substitute(Substitution(0, &attrs), body);
-        checkVarDefs(state.primOps, body);
-        return evalExpr(state, body);
-    } catch (Error & e) {
-        addErrorPrefix(e, "while evaluating the `with' body at %1%:\n",
-            showPos(pos));
-        throw;
-    } 
+
+    callFunction(fun, actualArgs, res);
 }
 
 
-LocalNoInline(Expr evalHasAttr(EvalState & state, Expr e, ATerm name))
+void ExprWith::eval(EvalState & state, Env & env, Value & v)
 {
-    ATermMap attrs;
-    queryAllAttrs(evalExpr(state, e), attrs);
-    return makeBool(attrs.get(name) != 0);
+    Env & env2(state.allocEnv(1));
+    env2.up = &env;
+    env2.prevWith = prevWith;
+
+    state.evalAttrs(env, attrs, env2.values[0]);
+
+    state.eval(env2, body, v);
 }
 
 
-LocalNoInline(Expr evalPlusConcat(EvalState & state, Expr e))
+void ExprIf::eval(EvalState & state, Env & env, Value & v)
 {
-    Expr e1, e2;
-    ATermList es;
+    state.eval(env, state.evalBool(env, cond) ? then : else_, v);
+}
+
     
-    ATermVector args;
+void ExprAssert::eval(EvalState & state, Env & env, Value & v)
+{
+    if (!state.evalBool(env, cond))
+        throwAssertionError("assertion failed at %1%", pos);
+    state.eval(env, body, v);
+}
+
     
-    if (matchOpPlus(e, e1, e2)) {
-
-        /* !!! Awful compatibility hack for `drv + /path'.
-           According to regular concatenation, /path should be
-           copied to the store and its store path should be
-           appended to the string.  However, in Nix <= 0.10, /path
-           was concatenated.  So handle that case separately, but
-           do print out a warning.  This code can go in Nix 0.12,
-           maybe. */
-        e1 = evalExpr(state, e1);
-        e2 = evalExpr(state, e2);
-
-        ATermList as;
-        ATerm p;
-        if (matchAttrs(e1, as) && matchPath(e2, p)) {
-            static bool haveWarned = false;
-            warnOnce(haveWarned, format(
-                    "concatenation of a derivation and a path is deprecated; "
-                    "you should write `drv + \"%1%\"' instead of `drv + %1%'")
-                % aterm2String(p));
-            PathSet context;
-            return makeStr(
-                coerceToString(state, makeSelect(e1, toATerm("outPath")), context)
-                + aterm2String(p), context);
-        }
+void ExprOpNot::eval(EvalState & state, Env & env, Value & v)
+{
+    mkBool(v, !state.evalBool(env, e));
+}
 
-        args.push_back(e1);
-        args.push_back(e2);
-    }
 
-    else if (matchConcatStrings(e, es))
-        for (ATermIterator i(es); i; ++i) args.push_back(*i);
-        
-    try {
-        return concatStrings(state, args);
-    } catch (Error & e) {
-        addErrorPrefix(e, "in a string concatenation:\n");
-        throw;
-    }
+void ExprOpEq::eval(EvalState & state, Env & env, Value & v)
+{
+    Value v1; state.eval(env, e1, v1);
+    Value v2; state.eval(env, e2, v2);
+    mkBool(v, state.eqValues(v1, v2));
 }
 
 
-LocalNoInline(Expr evalSubPath(EvalState & state, Expr e1, Expr e2))
+void ExprOpNEq::eval(EvalState & state, Env & env, Value & v)
 {
-    static bool haveWarned = false;
-    warnOnce(haveWarned, "the subpath operator (~) is deprecated, use string concatenation (+) instead");
-    ATermVector args;
-    args.push_back(e1);
-    args.push_back(e2);
-    return concatStrings(state, args, "/");
+    Value v1; state.eval(env, e1, v1);
+    Value v2; state.eval(env, e2, v2);
+    mkBool(v, !state.eqValues(v1, v2));
 }
 
 
-LocalNoInline(Expr evalOpConcat(EvalState & state, Expr e1, Expr e2))
+void ExprOpAnd::eval(EvalState & state, Env & env, Value & v)
 {
-    try {
-        ATermList l1 = evalList(state, e1);
-        ATermList l2 = evalList(state, e2);
-        return makeList(ATconcat(l1, l2));
-    } catch (Error & e) {
-        addErrorPrefix(e, "in a list concatenation:\n");
-        throw;
-    }
+    mkBool(v, state.evalBool(env, e1) && state.evalBool(env, e2));
 }
 
 
-/* Implementation of the `==' and `!=' operators. */
-LocalNoInline(bool areEqual(EvalState & state, Expr e1, Expr e2))
+void ExprOpOr::eval(EvalState & state, Env & env, Value & v)
 {
-    e1 = evalExpr(state, e1);
-    e2 = evalExpr(state, e2);
-
-    /* We cannot test functions/primops for equality, and we currently
-       don't support testing equality between attribute sets or lists
-       - that would have to be a deep equality test to be sound. */
-    AFun sym1 = ATgetAFun(e1);
-    AFun sym2 = ATgetAFun(e2);
+    mkBool(v, state.evalBool(env, e1) || state.evalBool(env, e2));
+}
 
-    if (sym1 != sym2) return false;
 
-    /* Functions are incomparable. */
-    if (sym1 == symFunction || sym1 == symPrimOp) return false;
+void ExprOpImpl::eval(EvalState & state, Env & env, Value & v)
+{
+    mkBool(v, !state.evalBool(env, e1) || state.evalBool(env, e2));
+}
 
-    if (!state.allowUnsafeEquality && sym1 == symAttrs)
-        throw EvalError("comparison of attribute sets is not implemented");
 
-    /* !!! This allows comparisons of infinite data structures to
-       succeed, such as `let x = [x]; in x == x'.  This is
-       undesirable, since equivalent (?) terms such as `let x = [x]; y
-       = [y]; in x == y' don't terminate. */
-    if (e1 == e2) return true;
+void ExprOpUpdate::eval(EvalState & state, Env & env, Value & v)
+{
+    Value v2;
+    state.evalAttrs(env, e1, v2);
+        
+    state.cloneAttrs(v2, v);
+        
+    state.evalAttrs(env, e2, v2);
     
-    if (sym1 == symList) {
-        ATermList es1; matchList(e1, es1);
-        ATermList es2; matchList(e2, es2);
-        if (ATgetLength(es1) != ATgetLength(es2)) return false;
-        ATermIterator i(es1), j(es2);
-        while (*i) {
-            if (!areEqual(state, *i, *j)) return false;
-            ++i; ++j;
+    foreach (Bindings::iterator, i, *v2.attrs) {
+        Attr & a = (*v.attrs)[i->first];
+        mkCopy(a.value, i->second.value);
+        a.pos = i->second.pos;
+    }
+}
+
+
+void ExprOpConcatLists::eval(EvalState & state, Env & env, Value & v)
+{
+    Value v1; state.eval(env, e1, v1);
+    state.forceList(v1);
+    Value v2; state.eval(env, e2, v2);
+    state.forceList(v2);
+    state.mkList(v, v1.list.length + v2.list.length);
+    for (unsigned int n = 0; n < v1.list.length; ++n)
+        v.list.elems[n] = v1.list.elems[n];
+    for (unsigned int n = 0; n < v2.list.length; ++n)
+        v.list.elems[n + v1.list.length] = v2.list.elems[n];
+}
+
+
+void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
+{
+    PathSet context;
+    std::ostringstream s;
+        
+    bool first = true, isPath = false;
+    Value vStr;
+
+    foreach (vector<Expr *>::iterator, i, *es) {
+        state.eval(env, *i, vStr);
+
+        /* If the first element is a path, then the result will also
+           be a path, we don't copy anything (yet - that's done later,
+           since paths are copied when they are used in a derivation),
+           and none of the strings are allowed to have contexts. */
+        if (first) {
+            isPath = vStr.type == tPath;
+            first = false;
         }
-        return true;
+            
+        s << state.coerceToString(vStr, context, false, !isPath);
     }
-    
-    return false;
+        
+    if (isPath && !context.empty())
+        throwEvalError("a string that refers to a store path cannot be appended to a path, in `%1%'", s.str());
+
+    if (isPath)
+        mkPath(v, s.str().c_str());
+    else
+        mkString(v, s.str(), context);
 }
 
 
-static char * deepestStack = (char *) -1; /* for measuring stack usage */
+void EvalState::forceValue(Value & v)
+{
+    if (v.type == tThunk) {
+        ValueType saved = v.type;
+        try {
+            v.type = tBlackhole;
+            eval(*v.thunk.env, v.thunk.expr, v);
+        } catch (Error & e) {
+            v.type = saved;
+            throw;
+        }
+    }
+    else if (v.type == tCopy) {
+        forceValue(*v.val);
+        v = *v.val;
+    }
+    else if (v.type == tApp)
+        callFunction(*v.app.left, *v.app.right, v);
+    else if (v.type == tBlackhole)
+        throwEvalError("infinite recursion encountered");
+}
 
 
-Expr evalExpr2(EvalState & state, Expr e)
+void EvalState::strictForceValue(Value & v)
 {
-    /* When changing this function, make sure that you don't cause a
-       (large) increase in stack consumption! */
-    
-    char x;
-    if (&x < deepestStack) deepestStack = &x;
+    forceValue(v);
     
-    Expr e1, e2, e3;
-    ATerm name, pos;
-    AFun sym = ATgetAFun(e);
-
-    /* Normal forms. */
-    if (sym == symStr ||
-        sym == symPath ||
-        sym == symNull ||
-        sym == symInt ||
-        sym == symBool ||
-        sym == symFunction ||
-        sym == symAttrs ||
-        sym == symList ||
-        sym == symPrimOp)
-        return e;
+    if (v.type == tAttrs) {
+        foreach (Bindings::iterator, i, *v.attrs)
+            strictForceValue(i->second.value);
+    }
     
-    /* The `Closed' constructor is just a way to prevent substitutions
-       into expressions not containing free variables. */
-    if (matchClosed(e, e1))
-        return evalExpr(state, e1);
-
-    /* Any encountered variables must be primops (since undefined
-       variables are detected after parsing). */
-    if (matchVar(e, name)) return evalVar(state, name);
-
-    /* Function application. */
-    if (matchCall(e, e1, e2)) return evalCall(state, e1, e2);
-
-    /* Attribute selection. */
-    if (matchSelect(e, e1, name)) return evalSelect(state, e1, name);
-
-    /* Mutually recursive sets. */
-    ATermList rbnds, nrbnds;
-    if (matchRec(e, rbnds, nrbnds))
-        return expandRec(state, e, rbnds, nrbnds);
-
-    /* Conditionals. */
-    if (matchIf(e, e1, e2, e3))
-        return evalExpr(state, evalBool(state, e1) ? e2 : e3);
-
-    /* Assertions. */
-    if (matchAssert(e, e1, e2, pos)) return evalAssert(state, e1, e2, pos);
-
-    /* Withs. */
-    if (matchWith(e, e1, e2, pos)) return evalWith(state, e1, e2, pos);
-
-    /* Generic equality/inequality.  Note that the behaviour on
-       composite data (lists, attribute sets) and functions is
-       undefined, since the subterms of those terms are not evaluated.
-       However, we don't want to make (==) strict, because that would
-       make operations like `big_derivation == null' very slow (unless
-       we were to evaluate them side-by-side). */
-    if (matchOpEq(e, e1, e2)) return makeBool(areEqual(state, e1, e2));
-        
-    if (matchOpNEq(e, e1, e2)) return makeBool(!areEqual(state, e1, e2));
-        
-    /* Negation. */
-    if (matchOpNot(e, e1))
-        return makeBool(!evalBool(state, e1));
+    else if (v.type == tList) {
+        for (unsigned int n = 0; n < v.list.length; ++n)
+            strictForceValue(*v.list.elems[n]);
+    }
+}
 
-    /* Implication. */
-    if (matchOpImpl(e, e1, e2))
-        return makeBool(!evalBool(state, e1) || evalBool(state, e2));
 
-    /* Conjunction (logical AND). */
-    if (matchOpAnd(e, e1, e2))
-        return makeBool(evalBool(state, e1) && evalBool(state, e2));
+int EvalState::forceInt(Value & v)
+{
+    forceValue(v);
+    if (v.type != tInt)
+        throwTypeError("value is %1% while an integer was expected", showType(v));
+    return v.integer;
+}
 
-    /* Disjunction (logical OR). */
-    if (matchOpOr(e, e1, e2))
-        return makeBool(evalBool(state, e1) || evalBool(state, e2));
 
-    /* Attribute set update (//). */
-    if (matchOpUpdate(e, e1, e2))
-        return updateAttrs(evalExpr(state, e1), evalExpr(state, e2));
+bool EvalState::forceBool(Value & v)
+{
+    forceValue(v);
+    if (v.type != tBool)
+        throwTypeError("value is %1% while a Boolean was expected", showType(v));
+    return v.boolean;
+}
+
 
-    /* Attribute existence test (?). */
-    if (matchOpHasAttr(e, e1, name)) return evalHasAttr(state, e1, name);
+void EvalState::forceAttrs(Value & v)
+{
+    forceValue(v);
+    if (v.type != tAttrs)
+        throwTypeError("value is %1% while an attribute set was expected", showType(v));
+}
 
-    /* String or path concatenation. */
-    if (sym == symOpPlus || sym == symConcatStrings)
-        return evalPlusConcat(state, e);
 
-    /* Backwards compatability: subpath operator (~). */
-    if (matchSubPath(e, e1, e2)) return evalSubPath(state, e1, e2);
+void EvalState::forceList(Value & v)
+{
+    forceValue(v);
+    if (v.type != tList)
+        throwTypeError("value is %1% while a list was expected", showType(v));
+}
 
-    /* List concatenation. */
-    if (matchOpConcat(e, e1, e2)) return evalOpConcat(state, e1, e2);
 
-    /* Barf. */
-    abort();
+void EvalState::forceFunction(Value & v)
+{
+    forceValue(v);
+    if (v.type != tLambda && v.type != tPrimOp && v.type != tPrimOpApp)
+        throwTypeError("value is %1% while a function was expected", showType(v));
 }
 
 
-Expr evalExpr(EvalState & state, Expr e)
+string EvalState::forceString(Value & v)
 {
-    checkInterrupt();
+    forceValue(v);
+    if (v.type != tString)
+        throwTypeError("value is %1% while a string was expected", showType(v));
+    return string(v.string.s);
+}
 
-#if 0
-    startNest(nest, lvlVomit,
-        format("evaluating expression: %1%") % e);
-#endif
-
-    state.nrEvaluated++;
-
-    /* Consult the memo table to quickly get the normal form of
-       previously evaluated expressions. */
-    Expr nf = state.normalForms.get(e);
-    if (nf) {
-        if (nf == makeBlackHole())
-            throwEvalError("infinite recursion encountered");
-        state.nrCached++;
-        return nf;
-    }
 
-    /* Otherwise, evaluate and memoize. */
-    state.normalForms.set(e, makeBlackHole());
-    try {
-        nf = evalExpr2(state, e);
-    } catch (Error & err) {
-        state.normalForms.remove(e);
-        throw;
-    }
-    state.normalForms.set(e, nf);
-    return nf;
+string EvalState::forceString(Value & v, PathSet & context)
+{
+    string s = forceString(v);
+    if (v.string.context)
+        for (const char * * p = v.string.context; *p; ++p) 
+            context.insert(*p);
+    return s;
 }
 
 
-Expr evalFile(EvalState & state, const Path & path)
+string EvalState::forceStringNoCtx(Value & v)
 {
-    startNest(nest, lvlTalkative, format("evaluating file `%1%'") % path);
-    Expr e = parseExprFromFile(state, path);
-    try {
-        return evalExpr(state, e);
-    } catch (Error & e) {
-        e.addPrefix(format("while evaluating the file `%1%':\n")
-            % path);
-        throw;
-    }
+    string s = forceString(v);
+    if (v.string.context)
+        throwEvalError("the string `%1%' is not allowed to refer to a store path (such as `%2%')",
+            v.string.s, v.string.context[0]);
+    return s;
 }
 
 
-static Expr strictEvalExpr(EvalState & state, Expr e, ATermMap & nfs);
+bool EvalState::isDerivation(Value & v)
+{
+    if (v.type != tAttrs) return false;
+    Bindings::iterator i = v.attrs->find(sType);
+    return i != v.attrs->end() && forceStringNoCtx(i->second.value) == "derivation";
+}
 
 
-static Expr strictEvalExpr_(EvalState & state, Expr e, ATermMap & nfs)
+string EvalState::coerceToString(Value & v, PathSet & context,
+    bool coerceMore, bool copyToStore)
 {
-    e = evalExpr(state, e);
+    forceValue(v);
 
-    ATermList as;
-    if (matchAttrs(e, as)) {
-        ATermList as2 = ATempty;
-        for (ATermIterator i(as); i; ++i) {
-            ATerm name; Expr e; ATerm pos;
-            if (!matchBind(*i, name, e, pos)) abort(); /* can't happen */
-            as2 = ATinsert(as2, makeBind(name, strictEvalExpr(state, e, nfs), pos));
-        }
-        return makeAttrs(ATreverse(as2));
+    string s;
+
+    if (v.type == tString) {
+        if (v.string.context) 
+            for (const char * * p = v.string.context; *p; ++p) 
+                context.insert(*p);
+        return v.string.s;
     }
-    
-    ATermList es;
-    if (matchList(e, es)) {
-        ATermList es2 = ATempty;
-        for (ATermIterator i(es); i; ++i)
-            es2 = ATinsert(es2, strictEvalExpr(state, *i, nfs));
-        return makeList(ATreverse(es2));
+
+    if (v.type == tPath) {
+        Path path(canonPath(v.path));
+
+        if (!copyToStore) return path;
+        
+        if (nix::isDerivation(path))
+            throwEvalError("file names are not allowed to end in `%1%'", drvExtension);
+
+        Path dstPath;
+        if (srcToStore[path] != "")
+            dstPath = srcToStore[path];
+        else {
+            dstPath = readOnlyMode
+                ? computeStorePathForPath(path).first
+                : store->addToStore(path);
+            srcToStore[path] = dstPath;
+            printMsg(lvlChatty, format("copied source `%1%' -> `%2%'")
+                % path % dstPath);
+        }
+
+        context.insert(dstPath);
+        return dstPath;
     }
-    
-    return e;
-}
 
+    if (v.type == tAttrs) {
+        Bindings::iterator i = v.attrs->find(sOutPath);
+        if (i == v.attrs->end())
+            throwTypeError("cannot coerce an attribute set (except a derivation) to a string");
+        return coerceToString(i->second.value, context, coerceMore, copyToStore);
+    }
 
-static Expr strictEvalExpr(EvalState & state, Expr e, ATermMap & nfs)
-{
-    Expr nf = nfs.get(e);
-    if (nf) return nf;
+    if (coerceMore) {
 
-    nf = strictEvalExpr_(state, e, nfs);
+        /* Note that `false' is represented as an empty string for
+           shell scripting convenience, just like `null'. */
+        if (v.type == tBool && v.boolean) return "1";
+        if (v.type == tBool && !v.boolean) return "";
+        if (v.type == tInt) return int2String(v.integer);
+        if (v.type == tNull) return "";
 
-    nfs.set(e, nf);
+        if (v.type == tList) {
+            string result;
+            for (unsigned int n = 0; n < v.list.length; ++n) {
+                result += coerceToString(*v.list.elems[n],
+                    context, coerceMore, copyToStore);
+                if (n < v.list.length - 1
+                    /* !!! not quite correct */
+                    && (v.list.elems[n]->type != tList || v.list.elems[n]->list.length != 0))
+                    result += " ";
+            }
+            return result;
+        }
+    }
     
-    return nf;
+    throwTypeError("cannot coerce %1% to a string", showType(v));
 }
 
 
-Expr strictEvalExpr(EvalState & state, Expr e)
+Path EvalState::coerceToPath(Value & v, PathSet & context)
 {
-    ATermMap strictNormalForms;
-    return strictEvalExpr(state, e, strictNormalForms);
+    string path = coerceToString(v, context, false, false);
+    if (path == "" || path[0] != '/')
+        throwEvalError("string `%1%' doesn't represent an absolute path", path);
+    return path;
 }
 
 
-/* Yes, this is a really bad idea... */
-extern "C" {
-    unsigned long AT_calcAllocatedSize();
+bool EvalState::eqValues(Value & v1, Value & v2)
+{
+    forceValue(v1);
+    forceValue(v2);
+
+    /* !!! Hack to support some old broken code that relies on pointer
+       equality tests between attribute sets.  (Specifically,
+       builderDefs calls uniqList on a list of attribute sets.)  Will
+       remove this eventually. */
+    if (&v1 == &v2) return true;
+
+    if (v1.type != v2.type) return false;
+
+    switch (v1.type) {
+
+        case tInt:
+            return v1.integer == v2.integer;
+
+        case tBool:
+            return v1.boolean == v2.boolean;
+
+        case tString: {
+            /* Compare both the string and its context. */
+            if (strcmp(v1.string.s, v2.string.s) != 0) return false;
+            const char * * p = v1.string.context, * * q = v2.string.context;
+            if (!p && !q) return true;
+            if (!p || !q) return false;
+            for ( ; *p && *q; ++p, ++q)
+                if (strcmp(*p, *q) != 0) return false;
+            if (*p || *q) return false;
+            return true;
+        }
+
+        case tPath:
+            return strcmp(v1.path, v2.path) == 0;
+
+        case tNull:
+            return true;
+
+        case tList:
+            if (v1.list.length != v2.list.length) return false;
+            for (unsigned int n = 0; n < v1.list.length; ++n)
+                if (!eqValues(*v1.list.elems[n], *v2.list.elems[n])) return false;
+            return true;
+
+        case tAttrs: {
+            if (v1.attrs->size() != v2.attrs->size()) return false;
+            Bindings::iterator i, j;
+            for (i = v1.attrs->begin(), j = v2.attrs->begin(); i != v1.attrs->end(); ++i, ++j)
+                if (i->first != j->first || !eqValues(i->second.value, j->second.value))
+                    return false;
+            return true;
+        }
+
+        /* Functions are incomparable. */
+        case tLambda:
+        case tPrimOp:
+        case tPrimOpApp:
+            return false;
+
+        default:
+            throwEvalError("cannot compare %1% with %2%", showType(v1), showType(v2));
+    }
 }
 
-void printEvalStats(EvalState & state)
+
+void EvalState::printStats()
 {
     char x;
     bool showStats = getEnv("NIX_SHOW_STATS", "0") != "0";
-    printMsg(showStats ? lvlInfo : lvlDebug,
-        format("evaluated %1% expressions, %2% cache hits, %3%%% efficiency, used %4% ATerm bytes, used %5% bytes of stack space")
-        % state.nrEvaluated % state.nrCached
-        % ((float) state.nrCached / (float) state.nrEvaluated * 100)
-        % AT_calcAllocatedSize()
-        % (&x - deepestStack));
-    if (showStats)
-        printATermMapStats();
+    Verbosity v = showStats ? lvlInfo : lvlDebug;
+    printMsg(v, "evaluation statistics:");
+    printMsg(v, format("  expressions evaluated: %1%") % nrEvaluated);
+    printMsg(v, format("  stack space used: %1% bytes") % (&x - deepestStack));
+    printMsg(v, format("  max eval() nesting depth: %1%") % maxRecursionDepth);
+    printMsg(v, format("  stack space per eval() level: %1% bytes")
+        % ((&x - deepestStack) / (float) maxRecursionDepth));
+    printMsg(v, format("  environments allocated: %1% (%2% bytes)")
+        % nrEnvs % (nrEnvs * sizeof(Env)));
+    printMsg(v, format("  values allocated in environments: %1% (%2% bytes)")
+        % nrValuesInEnvs % (nrValuesInEnvs * sizeof(Value)));
+    printMsg(v, format("  list elements: %1% (%2% bytes)")
+        % nrListElems % (nrListElems * sizeof(Value *)));
+    printMsg(v, format("  misc. values allocated: %1% (%2% bytes)")
+        % nrValues % (nrValues * sizeof(Value)));
+    printMsg(v, format("  symbols in symbol table: %1%") % symbols.size());
 }
 
- 
+
 }
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index fed6d3472..1a9862c29 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -3,17 +3,165 @@
 
 #include <map>
 
-#include "aterm.hh"
 #include "nixexpr.hh"
+#include "symbol-table.hh"
 
 
 namespace nix {
 
 
 class Hash;
-    
+class EvalState;
+struct Env;
+struct Value;
+struct Attr;
+
+typedef std::map<Symbol, Attr> Bindings;
+
+
+typedef enum {
+    tInt = 1,
+    tBool,
+    tString,
+    tPath,
+    tNull,
+    tAttrs,
+    tList,
+    tThunk,
+    tApp,
+    tLambda,
+    tCopy,
+    tBlackhole,
+    tPrimOp,
+    tPrimOpApp,
+} ValueType;
+
+
+typedef void (* PrimOp) (EvalState & state, Value * * args, Value & v);
+
+
+struct Value
+{
+    ValueType type;
+    union 
+    {
+        int integer;
+        bool boolean;
+        
+        /* Strings in the evaluator carry a so-called `context' (the
+           ATermList) which is a list of strings representing store
+           paths.  This is to allow users to write things like
+
+             "--with-freetype2-library=" + freetype + "/lib"
+
+           where `freetype' is a derivation (or a source to be copied
+           to the store).  If we just concatenated the strings without
+           keeping track of the referenced store paths, then if the
+           string is used as a derivation attribute, the derivation
+           will not have the correct dependencies in its inputDrvs and
+           inputSrcs.
+
+           The semantics of the context is as follows: when a string
+           with context C is used as a derivation attribute, then the
+           derivations in C will be added to the inputDrvs of the
+           derivation, and the other store paths in C will be added to
+           the inputSrcs of the derivations.
+
+           For canonicity, the store paths should be in sorted order. */
+        struct {
+            const char * s;
+            const char * * context; // must be in sorted order
+        } string;
+        
+        const char * path;
+        Bindings * attrs;
+        struct {
+            unsigned int length;
+            Value * * elems;
+        } list;
+        struct {
+            Env * env;
+            Expr * expr;
+        } thunk;
+        struct {
+            Value * left, * right;
+        } app;
+        struct {
+            Env * env;
+            ExprLambda * fun;
+        } lambda;
+        Value * val;
+        struct {
+            PrimOp fun;
+            char * name;
+            unsigned int arity;
+        } primOp;
+        struct {
+            Value * left, * right;
+            unsigned int argsLeft;
+        } primOpApp;
+    };
+};
+
+
+struct Env
+{
+    Env * up;
+    unsigned int prevWith; // nr of levels up to next `with' environment
+    Value values[0];
+};
+
+
+struct Attr
+{
+    Value value;
+    Pos * pos;
+    Attr() : pos(&noPos) { };
+};
+
+
+static inline void mkInt(Value & v, int n)
+{
+    v.type = tInt;
+    v.integer = n;
+}
+
+
+static inline void mkBool(Value & v, bool b)
+{
+    v.type = tBool;
+    v.boolean = b;
+}
+
+
+static inline void mkThunk(Value & v, Env & env, Expr * expr)
+{
+    v.type = tThunk;
+    v.thunk.env = &env;
+    v.thunk.expr = expr;
+}
+
+
+static inline void mkCopy(Value & v, Value & src)
+{
+    v.type = tCopy;
+    v.val = &src;
+}
+
+
+static inline void mkApp(Value & v, Value & left, Value & right)
+{
+    v.type = tApp;
+    v.app.left = &left;
+    v.app.right = &right;
+}
+
+
+void mkString(Value & v, const char * s);
+void mkString(Value & v, const string & s, const PathSet & context = PathSet());
+void mkPath(Value & v, const char * s);
+
 
-typedef std::map<Path, PathSet> DrvRoots;
 typedef std::map<Path, Hash> DrvHashes;
 
 /* Cache for calls to addToStore(); maps source paths to the store
@@ -22,75 +170,153 @@ typedef std::map<Path, Path> SrcToStore;
 
 struct EvalState;
 
-/* Note: using a ATermVector is safe here, since when we call a primop
-   we also have an ATermList on the stack. */
-typedef Expr (* PrimOp) (EvalState &, const ATermVector & args);
+
+std::ostream & operator << (std::ostream & str, Value & v);
 
 
-struct EvalState 
+class EvalState 
 {
-    ATermMap normalForms;
-    ATermMap primOps;
-    DrvRoots drvRoots;
+public:
     DrvHashes drvHashes; /* normalised derivation hashes */
-    SrcToStore srcToStore; 
 
-    unsigned int nrEvaluated;
-    unsigned int nrCached;
+    SymbolTable symbols;
+
+    const Symbol sWith, sOutPath, sDrvPath, sType, sMeta, sName, sSystem;
+
+private:
+    SrcToStore srcToStore; 
 
     bool allowUnsafeEquality;
 
+    std::map<Path, Expr *> parseTrees;
+
+public:
+    
     EvalState();
+    ~EvalState();
+
+    /* Evaluate an expression read from the given file to normal
+       form. */
+    void evalFile(const Path & path, Value & v);
+
+    /* Evaluate an expression to normal form, storing the result in
+       value `v'. */
+    void eval(Expr * e, Value & v);
+    void eval(Env & env, Expr * e, Value & v);
+
+    /* Evaluation the expression, then verify that it has the expected
+       type. */
+    bool evalBool(Env & env, Expr * e);
+    void evalAttrs(Env & env, Expr * e, Value & v);
+
+    /* If `v' is a thunk, enter it and overwrite `v' with the result
+       of the evaluation of the thunk.  If `v' is a delayed function
+       application, call the function and overwrite `v' with the
+       result.  Otherwise, this is a no-op. */
+    void forceValue(Value & v);
+
+    /* Force a value, then recursively force list elements and
+       attributes. */
+    void strictForceValue(Value & v);
+
+    /* Force `v', and then verify that it has the expected type. */
+    int forceInt(Value & v);
+    bool forceBool(Value & v);
+    void forceAttrs(Value & v);
+    void forceList(Value & v);
+    void forceFunction(Value & v); // either lambda or primop
+    string forceString(Value & v);
+    string forceString(Value & v, PathSet & context);
+    string forceStringNoCtx(Value & v);
+
+    /* Return true iff the value `v' denotes a derivation (i.e. a
+       set with attribute `type = "derivation"'). */
+    bool isDerivation(Value & v);
+
+    /* String coercion.  Converts strings, paths and derivations to a
+       string.  If `coerceMore' is set, also converts nulls, integers,
+       booleans and lists to a string.  If `copyToStore' is set,
+       referenced paths are copied to the Nix store as a side effect.q */
+    string coerceToString(Value & v, PathSet & context,
+        bool coerceMore = false, bool copyToStore = true);
+
+    /* Path coercion.  Converts strings, paths and derivations to a
+       path.  The result is guaranteed to be a canonicalised, absolute
+       path.  Nothing is copied to the store. */
+    Path coerceToPath(Value & v, PathSet & context);
+
+private:
+
+    /* The base environment, containing the builtin functions and
+       values. */
+    Env & baseEnv;
+
+    unsigned int baseEnvDispl;
+
+public:
+    
+    /* The same, but used during parsing to resolve variables. */
+    StaticEnv staticBaseEnv; // !!! should be private
+
+private:
+    
+    void createBaseEnv();
+    
+    void addConstant(const string & name, Value & v);
 
-    void addPrimOps();
     void addPrimOp(const string & name,
         unsigned int arity, PrimOp primOp);
-};
 
+    Value * lookupVar(Env * env, const VarRef & var);
+    
+    friend class ExprVar;
+    friend class ExprAttrs;
+    friend class ExprLet;
 
-/* Evaluate an expression to normal form. */
-Expr evalExpr(EvalState & state, Expr e);
+public:
+    
+    /* Do a deep equality test between two values.  That is, list
+       elements and attributes are compared recursively. */
+    bool eqValues(Value & v1, Value & v2);
 
-/* Evaluate an expression read from the given file to normal form. */
-Expr evalFile(EvalState & state, const Path & path);
+    void callFunction(Value & fun, Value & arg, Value & v);
 
-/* Evaluate an expression, and recursively evaluate list elements and
-   attributes.  If `canonicalise' is true, we remove things like
-   position information and make sure that attribute sets are in
-   sorded order. */
-Expr strictEvalExpr(EvalState & state, Expr e);
+    /* Automatically call a function for which each argument has a
+       default value or has a binding in the `args' map. */
+    void autoCallFunction(const Bindings & args, Value & fun, Value & res);
+    
+    /* Allocation primitives. */
+    Value * allocValues(unsigned int count);
+    Env & allocEnv(unsigned int size);
 
-/* Specific results. */
-string evalString(EvalState & state, Expr e, PathSet & context);
-string evalStringNoCtx(EvalState & state, Expr e);
-int evalInt(EvalState & state, Expr e);
-bool evalBool(EvalState & state, Expr e);
-ATermList evalList(EvalState & state, Expr e);
+    void mkList(Value & v, unsigned int length);
+    void mkAttrs(Value & v);
+    void mkThunk_(Value & v, Expr * expr);
+    
+    void cloneAttrs(Value & src, Value & dst);
 
-/* Flatten nested lists into a single list (or expand a singleton into
-   a list). */
-ATermList flattenList(EvalState & state, Expr e);
+    /* Print statistics. */
+    void printStats();
 
-/* String coercion.  Converts strings, paths and derivations to a
-   string.  If `coerceMore' is set, also converts nulls, integers,
-   booleans and lists to a string. */
-string coerceToString(EvalState & state, Expr e, PathSet & context,
-    bool coerceMore = false, bool copyToStore = true);
+private:
+    
+    unsigned long nrEnvs;
+    unsigned long nrValuesInEnvs;
+    unsigned long nrValues;
+    unsigned long nrListElems;
+    unsigned long nrEvaluated;
+    unsigned int recursionDepth;
+    unsigned int maxRecursionDepth;
+    char * deepestStack; /* for measuring stack usage */
+    
+    friend class RecursionCounter;
+};
 
-/* Path coercion.  Converts strings, paths and derivations to a path.
-   The result is guaranteed to be an canonicalised, absolute path.
-   Nothing is copied to the store. */
-Path coerceToPath(EvalState & state, Expr e, PathSet & context);
 
-/* Automatically call a function for which each argument has a default
-   value or has a binding in the `args' map.  Note: result is a call,
-   not a normal form; it should be evaluated by calling evalExpr(). */
-Expr autoCallFunction(Expr e, const ATermMap & args);
+/* Return a string representing the type of the value `v'. */
+string showType(const Value & v);
 
-/* Print statistics. */
-void printEvalStats(EvalState & state);
 
- 
 }
 
 
diff --git a/src/libexpr/expr-to-xml.cc b/src/libexpr/expr-to-xml.cc
deleted file mode 100644
index 1e59eebfc..000000000
--- a/src/libexpr/expr-to-xml.cc
+++ /dev/null
@@ -1,186 +0,0 @@
-#include "expr-to-xml.hh"
-#include "xml-writer.hh"
-#include "nixexpr-ast.hh"
-#include "aterm.hh"
-#include "util.hh"
-
-#include <cstdlib>
-
-
-namespace nix {
-
-    
-static XMLAttrs singletonAttrs(const string & name, const string & value)
-{
-    XMLAttrs attrs;
-    attrs[name] = value;
-    return attrs;
-}
-
-
-/* set<Expr> is safe because all the expressions are also reachable
-   from the stack, therefore can't be garbage-collected. */
-typedef set<Expr> ExprSet;
-
-
-static void printTermAsXML(Expr e, XMLWriter & doc, PathSet & context,
-    ExprSet & drvsSeen, bool location);
-
-
-static void showAttrs(const ATermMap & attrs, XMLWriter & doc,
-    PathSet & context, ExprSet & drvsSeen, bool location)
-{
-    StringSet names;
-    for (ATermMap::const_iterator i = attrs.begin(); i != attrs.end(); ++i)
-        names.insert(aterm2String(i->key));
-    for (StringSet::iterator i = names.begin(); i != names.end(); ++i) {
-        ATerm attrRHS = attrs.get(toATerm(*i));
-	ATerm attr;
-	Pos pos;
-	XMLAttrs xmlAttrs;
-
-	xmlAttrs["name"] = *i;
-	if(matchAttrRHS(attrRHS, attr, pos)) {
-	    ATerm path;
-	    int line, column;
-            if (location && matchPos(pos, path, line, column)) {
-		xmlAttrs["path"] = aterm2String(path);
-		xmlAttrs["line"] = (format("%1%") % line).str();
-		xmlAttrs["column"] = (format("%1%") % column).str();
-	    }
-	} else
-	    abort(); // Should not happen.
-
-        XMLOpenElement _(doc, "attr", xmlAttrs);
-        printTermAsXML(attr, doc, context, drvsSeen, location);
-    }
-}
-
-
-static void printPatternAsXML(Pattern pat, XMLWriter & doc)
-{
-    ATerm name;
-    ATermList formals;
-    Pattern pat1, pat2;
-    ATermBool ellipsis;
-    if (matchVarPat(pat, name))
-        doc.writeEmptyElement("varpat", singletonAttrs("name", aterm2String(name)));
-    else if (matchAttrsPat(pat, formals, ellipsis)) {
-        XMLOpenElement _(doc, "attrspat");
-        for (ATermIterator i(formals); i; ++i) {
-            Expr name; ATerm dummy;
-            if (!matchFormal(*i, name, dummy)) abort();
-            doc.writeEmptyElement("attr", singletonAttrs("name", aterm2String(name)));
-        }
-        if (ellipsis == eTrue) doc.writeEmptyElement("ellipsis");
-    }
-    else if (matchAtPat(pat, pat1, pat2)) {
-        XMLOpenElement _(doc, "at");
-        printPatternAsXML(pat1, doc);
-        printPatternAsXML(pat2, doc);
-    }
-}
-
-
-static void printTermAsXML(Expr e, XMLWriter & doc, PathSet & context,
-    ExprSet & drvsSeen, bool location)
-{
-    XMLAttrs attrs;
-    string s;
-    ATerm s2;
-    int i;
-    ATermList as, es;
-    ATerm pat, body, pos;
-
-    checkInterrupt();
-
-    if (matchStr(e, s, context)) /* !!! show the context? */
-        doc.writeEmptyElement("string", singletonAttrs("value", s));
-
-    else if (matchPath(e, s2))
-        doc.writeEmptyElement("path", singletonAttrs("value", aterm2String(s2)));
-
-    else if (matchNull(e))
-        doc.writeEmptyElement("null");
-
-    else if (matchInt(e, i))
-        doc.writeEmptyElement("int", singletonAttrs("value", (format("%1%") % i).str()));
-
-    else if (e == eTrue)
-        doc.writeEmptyElement("bool", singletonAttrs("value", "true"));
-
-    else if (e == eFalse)
-        doc.writeEmptyElement("bool", singletonAttrs("value", "false"));
-
-    else if (matchAttrs(e, as)) {
-        ATermMap attrs;
-        queryAllAttrs(e, attrs, true);
-
-        Expr aRHS = attrs.get(toATerm("type"));
-	Expr a = NULL;
-	if (aRHS)
-	    matchAttrRHS(aRHS, a, pos);
-        if (a && matchStr(a, s, context) && s == "derivation") {
-
-            XMLAttrs xmlAttrs;
-            Path outPath, drvPath;
-
-            aRHS = attrs.get(toATerm("drvPath"));
-            matchAttrRHS(aRHS, a, pos);
-            if (matchStr(a, drvPath, context))
-                xmlAttrs["drvPath"] = drvPath;
-
-            aRHS = attrs.get(toATerm("outPath"));
-            matchAttrRHS(aRHS, a, pos);
-            if (matchStr(a, outPath, context))
-                xmlAttrs["outPath"] = outPath;
-
-            XMLOpenElement _(doc, "derivation", xmlAttrs);
-
-            if (drvsSeen.find(e) == drvsSeen.end()) {
-                drvsSeen.insert(e);
-                showAttrs(attrs, doc, context, drvsSeen, location);
-            } else
-                doc.writeEmptyElement("repeated");
-        }
-
-        else {
-            XMLOpenElement _(doc, "attrs");
-            showAttrs(attrs, doc, context, drvsSeen, location);
-        }
-    }
-
-    else if (matchList(e, es)) {
-        XMLOpenElement _(doc, "list");
-        for (ATermIterator i(es); i; ++i)
-            printTermAsXML(*i, doc, context, drvsSeen, location);
-    }
-
-    else if (matchFunction(e, pat, body, pos)) {
-        ATerm path;
-	int line, column;
-	XMLAttrs xmlAttrs;
-	if (location && matchPos(pos, path, line, column)) {
-	    xmlAttrs["path"] = aterm2String(path);
-	    xmlAttrs["line"] = (format("%1%") % line).str();
-	    xmlAttrs["column"] = (format("%1%") % column).str();
-	}
-	XMLOpenElement _(doc, "function", xmlAttrs);
-        printPatternAsXML(pat, doc);
-    }
-
-    else
-        doc.writeEmptyElement("unevaluated");
-}
-
-
-void printTermAsXML(Expr e, std::ostream & out, PathSet & context, bool location)
-{
-    XMLWriter doc(true, out);
-    XMLOpenElement root(doc, "expr");
-    ExprSet drvsSeen;    
-    printTermAsXML(e, doc, context, drvsSeen, location);
-}
-
- 
-}
diff --git a/src/libexpr/expr-to-xml.hh b/src/libexpr/expr-to-xml.hh
deleted file mode 100644
index de9d55f32..000000000
--- a/src/libexpr/expr-to-xml.hh
+++ /dev/null
@@ -1,16 +0,0 @@
-#ifndef __EXPR_TO_XML_H
-#define __EXPR_TO_XML_H
-
-#include <string>
-#include <map>
-
-#include "nixexpr.hh"
-#include "aterm.hh"
-
-namespace nix {
-
-void printTermAsXML(Expr e, std::ostream & out, PathSet & context, bool location = false);
-    
-}
-
-#endif /* !__EXPR_TO_XML_H */
diff --git a/src/libexpr/get-drvs.cc b/src/libexpr/get-drvs.cc
index 1442d7988..82a92416b 100644
--- a/src/libexpr/get-drvs.cc
+++ b/src/libexpr/get-drvs.cc
@@ -1,5 +1,4 @@
 #include "get-drvs.hh"
-#include "nixexpr-ast.hh"
 #include "util.hh"
 
 
@@ -8,17 +7,10 @@ namespace nix {
 
 string DrvInfo::queryDrvPath(EvalState & state) const
 {
-    if (drvPath == "") {
-        Expr a = attrs->get(toATerm("drvPath"));
-
-        /* Backwards compatibility hack with user environments made by
-           Nix <= 0.10: these contain illegal Path("") expressions. */
-        ATerm t;
-        if (a && matchPath(evalExpr(state, a), t))
-            return aterm2String(t);
-        
+    if (drvPath == "" && attrs) {
+        Bindings::iterator i = attrs->find(state.sDrvPath);
         PathSet context;
-        (string &) drvPath = a ? coerceToPath(state, a, context) : "";
+        (string &) drvPath = i != attrs->end() ? state.coerceToPath(i->second.value, context) : "";
     }
     return drvPath;
 }
@@ -26,11 +18,10 @@ string DrvInfo::queryDrvPath(EvalState & state) const
 
 string DrvInfo::queryOutPath(EvalState & state) const
 {
-    if (outPath == "") {
-        Expr a = attrs->get(toATerm("outPath"));
-        if (!a) throw TypeError("output path missing");
+    if (outPath == "" && attrs) {
+        Bindings::iterator i = attrs->find(state.sOutPath);
         PathSet context;
-        (string &) outPath = coerceToPath(state, a, context);
+        (string &) outPath = i != attrs->end() ? state.coerceToPath(i->second.value, context) : "";
     }
     return outPath;
 }
@@ -38,35 +29,30 @@ string DrvInfo::queryOutPath(EvalState & state) const
 
 MetaInfo DrvInfo::queryMetaInfo(EvalState & state) const
 {
-    MetaInfo meta;
+    if (metaInfoRead) return meta;
     
-    Expr a = attrs->get(toATerm("meta"));
-    if (!a) return meta; /* fine, empty meta information */
+    (bool &) metaInfoRead = true;
+    
+    Bindings::iterator a = attrs->find(state.sMeta);
+    if (a == attrs->end()) return meta; /* fine, empty meta information */
 
-    ATermMap attrs2;
-    queryAllAttrs(evalExpr(state, a), attrs2);
+    state.forceAttrs(a->second.value);
 
-    for (ATermMap::const_iterator i = attrs2.begin(); i != attrs2.end(); ++i) {
-        Expr e = evalExpr(state, i->value);
-        string s;
-        PathSet context;
+    foreach (Bindings::iterator, i, *a->second.value.attrs) {
         MetaValue value;
-        int n;
-        ATermList es;
-        if (matchStr(e, s, context)) {
+        state.forceValue(i->second.value);
+        if (i->second.value.type == tString) {
             value.type = MetaValue::tpString;
-            value.stringValue = s;
-            meta[aterm2String(i->key)] = value;
-        } else if (matchInt(e, n)) {
+            value.stringValue = i->second.value.string.s;
+        } else if (i->second.value.type == tInt) {
             value.type = MetaValue::tpInt;
-            value.intValue = n;
-            meta[aterm2String(i->key)] = value;
-        } else if (matchList(e, es)) {
+            value.intValue = i->second.value.integer;
+        } else if (i->second.value.type == tList) {
             value.type = MetaValue::tpStrings;
-            for (ATermIterator j(es); j; ++j)
-                value.stringValues.push_back(evalStringNoCtx(state, *j));
-            meta[aterm2String(i->key)] = value;
-        }
+            for (unsigned int j = 0; j < i->second.value.list.length; ++j)
+                value.stringValues.push_back(state.forceStringNoCtx(*i->second.value.list.elems[j]));
+        } else continue;
+        ((MetaInfo &) meta)[i->first] = value;
     }
 
     return meta;
@@ -82,73 +68,46 @@ MetaValue DrvInfo::queryMetaInfo(EvalState & state, const string & name) const
 
 void DrvInfo::setMetaInfo(const MetaInfo & meta)
 {
-    ATermMap metaAttrs;
-    foreach (MetaInfo::const_iterator, i, meta) {
-        Expr e;
-        switch (i->second.type) {
-            case MetaValue::tpInt: e = makeInt(i->second.intValue); break;
-            case MetaValue::tpString: e = makeStr(i->second.stringValue); break;
-            case MetaValue::tpStrings: {
-                ATermList es = ATempty;
-                foreach (Strings::const_iterator, j, i->second.stringValues)
-                    es = ATinsert(es, makeStr(*j));
-                e = makeList(ATreverse(es));
-                break;
-            }
-            default: abort();
-        }
-        metaAttrs.set(toATerm(i->first), makeAttrRHS(e, makeNoPos()));
-    }
-    attrs->set(toATerm("meta"), makeAttrs(metaAttrs));
+    metaInfoRead = true;
+    this->meta = meta;
 }
 
 
-/* Cache for already evaluated derivations.  Usually putting ATerms in
-   a STL container is unsafe (they're not scanning for GC roots), but
-   here it doesn't matter; everything in this set is reachable from
-   the stack as well. */
-typedef set<Expr> Exprs;
+/* Cache for already considered attrsets. */
+typedef set<Bindings *> Done;
 
 
-/* Evaluate expression `e'.  If it evaluates to an attribute set of
-   type `derivation', then put information about it in `drvs' (unless
-   it's already in `doneExprs').  The result boolean indicates whether
-   it makes sense for the caller to recursively search for derivations
-   in `e'. */
-static bool getDerivation(EvalState & state, Expr e,
-    const string & attrPath, DrvInfos & drvs, Exprs & doneExprs)
+/* Evaluate value `v'.  If it evaluates to an attribute set of type
+   `derivation', then put information about it in `drvs' (unless it's
+   already in `doneExprs').  The result boolean indicates whether it
+   makes sense for the caller to recursively search for derivations in
+   `v'. */
+static bool getDerivation(EvalState & state, Value & v,
+    const string & attrPath, DrvInfos & drvs, Done & done)
 {
     try {
-        
-        ATermList es;
-        e = evalExpr(state, e);
-        if (!matchAttrs(e, es)) return true;
-
-        boost::shared_ptr<ATermMap> attrs(new ATermMap());
-        queryAllAttrs(e, *attrs, false);
-        
-        Expr a = attrs->get(toATerm("type"));
-        if (!a || evalStringNoCtx(state, a) != "derivation") return true;
+        state.forceValue(v);
+        if (!state.isDerivation(v)) return true;
 
         /* Remove spurious duplicates (e.g., an attribute set like
            `rec { x = derivation {...}; y = x;}'. */
-        if (doneExprs.find(e) != doneExprs.end()) return false;
-        doneExprs.insert(e);
+        if (done.find(v.attrs) != done.end()) return false;
+        done.insert(v.attrs);
 
         DrvInfo drv;
     
-        a = attrs->get(toATerm("name"));
+        Bindings::iterator i = v.attrs->find(state.sName);
         /* !!! We really would like to have a decent back trace here. */
-        if (!a) throw TypeError("derivation name missing");
-        drv.name = evalStringNoCtx(state, a);
+        if (i == v.attrs->end()) throw TypeError("derivation name missing");
+        drv.name = state.forceStringNoCtx(i->second.value);
 
-        a = attrs->get(toATerm("system"));
-        if (!a)
+        i = v.attrs->find(state.sSystem);
+        if (i == v.attrs->end())
             drv.system = "unknown";
         else
-            drv.system = evalStringNoCtx(state, a);
+            drv.system = state.forceStringNoCtx(i->second.value);
 
-        drv.attrs = attrs;
+        drv.attrs = v.attrs;
 
         drv.attrPath = attrPath;
 
@@ -161,11 +120,11 @@ static bool getDerivation(EvalState & state, Expr e,
 }
 
 
-bool getDerivation(EvalState & state, Expr e, DrvInfo & drv)
+bool getDerivation(EvalState & state, Value & v, DrvInfo & drv)
 {
-    Exprs doneExprs;
+    Done done;
     DrvInfos drvs;
-    getDerivation(state, e, "", drvs, doneExprs);
+    getDerivation(state, v, "", drvs, done);
     if (drvs.size() != 1) return false;
     drv = drvs.front();
     return true;
@@ -178,83 +137,73 @@ static string addToPath(const string & s1, const string & s2)
 }
 
 
-static void getDerivations(EvalState & state, Expr e,
-    const string & pathPrefix, const ATermMap & autoArgs,
-    DrvInfos & drvs, Exprs & doneExprs)
+static void getDerivations(EvalState & state, Value & vIn,
+    const string & pathPrefix, const Bindings & autoArgs,
+    DrvInfos & drvs, Done & done)
 {
-    e = evalExpr(state, autoCallFunction(evalExpr(state, e), autoArgs));
-
+    Value v;
+    state.autoCallFunction(autoArgs, vIn, v);
+    
     /* Process the expression. */
-    ATermList es;
     DrvInfo drv;
 
-    if (!getDerivation(state, e, pathPrefix, drvs, doneExprs))
-        return;
+    if (!getDerivation(state, v, pathPrefix, drvs, done)) ;
 
-    if (matchAttrs(e, es)) {
-        ATermMap drvMap(ATgetLength(es));
-        queryAllAttrs(e, drvMap);
+    else if (v.type == tAttrs) {
 
         /* !!! undocumented hackery to support combining channels in
            nix-env.cc. */
-        bool combineChannels = drvMap.get(toATerm("_combineChannels"));
+        bool combineChannels = v.attrs->find(state.symbols.create("_combineChannels")) != v.attrs->end();
 
         /* Consider the attributes in sorted order to get more
            deterministic behaviour in nix-env operations (e.g. when
            there are names clashes between derivations, the derivation
            bound to the attribute with the "lower" name should take
            precedence). */
-        typedef std::map<string, Expr> AttrsSorted;
-        AttrsSorted attrsSorted;
-        foreach (ATermMap::const_iterator, i, drvMap)
-            attrsSorted[aterm2String(i->key)] = i->value;
+        typedef std::map<string, Symbol> SortedSymbols;
+        SortedSymbols attrs;
+        foreach (Bindings::iterator, i, *v.attrs)
+            attrs.insert(std::pair<string, Symbol>(i->first, i->first));
 
-        foreach (AttrsSorted::iterator, i, attrsSorted) {
+        foreach (SortedSymbols::iterator, i, attrs) {
             startNest(nest, lvlDebug, format("evaluating attribute `%1%'") % i->first);
             string pathPrefix2 = addToPath(pathPrefix, i->first);
+            Value & v2((*v.attrs)[i->second].value);
             if (combineChannels)
-                getDerivations(state, i->second, pathPrefix2, autoArgs, drvs, doneExprs);
-            else if (getDerivation(state, i->second, pathPrefix2, drvs, doneExprs)) {
+                getDerivations(state, v2, pathPrefix2, autoArgs, drvs, done);
+            else if (getDerivation(state, v2, pathPrefix2, drvs, done)) {
                 /* If the value of this attribute is itself an
                    attribute set, should we recurse into it?  => Only
                    if it has a `recurseForDerivations = true'
                    attribute. */
-                ATermList es;
-                Expr e = evalExpr(state, i->second), e2;
-                if (matchAttrs(e, es)) {
-                    ATermMap attrs(ATgetLength(es));
-                    queryAllAttrs(e, attrs, false);
-                    if (((e2 = attrs.get(toATerm("recurseForDerivations")))
-                            && evalBool(state, e2)))
-                        getDerivations(state, e, pathPrefix2, autoArgs, drvs, doneExprs);
+                if (v2.type == tAttrs) {
+                    Bindings::iterator j = v2.attrs->find(state.symbols.create("recurseForDerivations"));
+                    if (j != v2.attrs->end() && state.forceBool(j->second.value))
+                        getDerivations(state, v2, pathPrefix2, autoArgs, drvs, done);
                 }
             }
         }
-        
-        return;
     }
 
-    if (matchList(e, es)) {
-        int n = 0;
-        for (ATermIterator i(es); i; ++i, ++n) {
+    else if (v.type == tList) {
+        for (unsigned int n = 0; n < v.list.length; ++n) {
             startNest(nest, lvlDebug,
                 format("evaluating list element"));
             string pathPrefix2 = addToPath(pathPrefix, (format("%1%") % n).str());
-            if (getDerivation(state, *i, pathPrefix2, drvs, doneExprs))
-                getDerivations(state, *i, pathPrefix2, autoArgs, drvs, doneExprs);
+            if (getDerivation(state, *v.list.elems[n], pathPrefix2, drvs, done))
+                getDerivations(state, *v.list.elems[n], pathPrefix2, autoArgs, drvs, done);
         }
-        return;
     }
 
-    throw TypeError("expression does not evaluate to a derivation (or a set or list of those)");
+    else throw TypeError("expression does not evaluate to a derivation (or a set or list of those)");
 }
 
 
-void getDerivations(EvalState & state, Expr e, const string & pathPrefix,
-    const ATermMap & autoArgs, DrvInfos & drvs)
+void getDerivations(EvalState & state, Value & v, const string & pathPrefix,
+    const Bindings & autoArgs, DrvInfos & drvs)
 {
-    Exprs doneExprs;
-    getDerivations(state, e, pathPrefix, autoArgs, drvs, doneExprs);
+    Done done;
+    getDerivations(state, v, pathPrefix, autoArgs, drvs, done);
 }
 
  
diff --git a/src/libexpr/get-drvs.hh b/src/libexpr/get-drvs.hh
index b56f54711..ca7d98002 100644
--- a/src/libexpr/get-drvs.hh
+++ b/src/libexpr/get-drvs.hh
@@ -29,16 +29,19 @@ struct DrvInfo
 private:
     string drvPath;
     string outPath;
+
+    bool metaInfoRead;
+    MetaInfo meta;
     
 public:
     string name;
     string attrPath; /* path towards the derivation */
     string system;
 
-    /* !!! these should really be hidden, and setMetaInfo() should
-       make a copy since the ATermMap can be shared between multiple
-       DrvInfos. */
-    boost::shared_ptr<ATermMap> attrs;
+    /* !!! make this private */
+    Bindings * attrs;
+
+    DrvInfo() : metaInfoRead(false), attrs(0) { };
 
     string queryDrvPath(EvalState & state) const;
     string queryOutPath(EvalState & state) const;
@@ -62,13 +65,12 @@ public:
 typedef list<DrvInfo> DrvInfos;
 
 
-/* Evaluate expression `e'.  If it evaluates to a derivation, store
-   information about the derivation in `drv' and return true.
-   Otherwise, return false. */
-bool getDerivation(EvalState & state, Expr e, DrvInfo & drv);
+/* If value `v' denotes a derivation, store information about the
+   derivation in `drv' and return true.  Otherwise, return false. */
+bool getDerivation(EvalState & state, Value & v, DrvInfo & drv);
 
-void getDerivations(EvalState & state, Expr e, const string & pathPrefix,
-    const ATermMap & autoArgs, DrvInfos & drvs);
+void getDerivations(EvalState & state, Value & v, const string & pathPrefix,
+    const Bindings & autoArgs, DrvInfos & drvs);
 
  
 }
diff --git a/src/libexpr/lexer.l b/src/libexpr/lexer.l
index 81aec99e1..f29f9b684 100644
--- a/src/libexpr/lexer.l
+++ b/src/libexpr/lexer.l
@@ -8,9 +8,7 @@
 
 
 %{
-#include "aterm.hh"
 #include "nixexpr.hh"
-#include "nixexpr-ast.hh"
 #define BISON_HEADER_HACK
 #include "parser-tab.hh"
 
@@ -21,13 +19,16 @@ namespace nix {
     
 static void initLoc(YYLTYPE * loc)
 {
-    loc->first_line = 1;
-    loc->first_column = 1;
+    loc->first_line = loc->last_line = 1;
+    loc->first_column = loc->last_column = 1;
 }
 
     
 static void adjustLoc(YYLTYPE * loc, const char * s, size_t len)
 {
+    loc->first_line = loc->last_line;
+    loc->first_column = loc->last_column;
+
     while (len--) {
        switch (*s++) {
        case '\r':
@@ -35,17 +36,17 @@ static void adjustLoc(YYLTYPE * loc, const char * s, size_t len)
                s++;
            /* fall through */
        case '\n': 
-           ++loc->first_line;
-           loc->first_column = 1;
+           ++loc->last_line;
+           loc->last_column = 1;
            break;
        default:
-           ++loc->first_column;
+           ++loc->last_column;
        }
     }
 }
 
 
-static Expr unescapeStr(const char * s)
+static Expr * unescapeStr(const char * s)
 {
     string t;
     char c;
@@ -65,7 +66,7 @@ static Expr unescapeStr(const char * s)
         }
         else t += c;
     }
-    return makeStr(toATerm(t), ATempty);
+    return new ExprString(t);
 }
 
  
@@ -105,19 +106,20 @@ inherit     { return INHERIT; }
 \/\/        { return UPDATE; }
 \+\+        { return CONCAT; }
 
-{ID}        { yylval->t = toATerm(yytext); return ID; /* !!! alloc */ }
+{ID}        { yylval->id = strdup(yytext); return ID; }
 {INT}       { int n = atoi(yytext); /* !!! overflow */
-              yylval->t = ATmake("<int>", n);
+              yylval->n = n;
               return INT;
             }
 
 \"          { BEGIN(STRING); return '"'; }
 <STRING>([^\$\"\\]|\$[^\{\"]|\\.)+ {
-/* !!! Not quite right: we want a follow restriction on "$", it
-   shouldn't be followed by a "{".  Right now "$\"" will be consumed
-   as part of a string, rather than a "$" followed by the string
-   terminator.  Disallow "$\"" for now. */
-              yylval->t = unescapeStr(yytext); /* !!! alloc */ 
+              /* !!! Not quite right: we want a follow restriction on
+                 "$", it shouldn't be followed by a "{".  Right now
+                 "$\"" will be consumed as part of a string, rather
+                 than a "$" followed by the string terminator.
+                 Disallow "$\"" for now. */
+              yylval->e = unescapeStr(yytext);
               return STR;
             }
 <STRING>\$\{  { BEGIN(INITIAL); return DOLLAR_CURLY; }
@@ -126,31 +128,31 @@ inherit     { return INHERIT; }
 
 \'\'(\ *\n)?     { BEGIN(IND_STRING); return IND_STRING_OPEN; }
 <IND_STRING>([^\$\']|\$[^\{\']|\'[^\'\$])+ {
-                   yylval->t = makeIndStr(toATerm(yytext));
+                   yylval->e = new ExprIndStr(yytext);
                    return IND_STR;
                  }
 <IND_STRING>\'\'\$ {
-                   yylval->t = makeIndStr(toATerm("$"));
+                   yylval->e = new ExprIndStr("$");
                    return IND_STR;
                  }
 <IND_STRING>\'\'\' {
-                   yylval->t = makeIndStr(toATerm("''"));
+                   yylval->e = new ExprIndStr("''");
                    return IND_STR;
                  }
 <IND_STRING>\'\'\\. {
-                   yylval->t = unescapeStr(yytext + 2);
+                   yylval->e = unescapeStr(yytext + 2);
                    return IND_STR;
                  }
 <IND_STRING>\$\{ { BEGIN(INITIAL); return DOLLAR_CURLY; }
 <IND_STRING>\'\' { BEGIN(INITIAL); return IND_STRING_CLOSE; }
 <IND_STRING>\'   {
-                   yylval->t = makeIndStr(toATerm("'"));
+                   yylval->e = new ExprIndStr("'");
                    return IND_STR;
                  }
 <IND_STRING>.    return yytext[0]; /* just in case: shouldn't be reached */
 
-{PATH}      { yylval->t = toATerm(yytext); return PATH; /* !!! alloc */ }
-{URI}       { yylval->t = toATerm(yytext); return URI; /* !!! alloc */ }
+{PATH}      { yylval->path = strdup(yytext); return PATH; }
+{URI}       { yylval->uri = strdup(yytext); return URI; }
 
 [ \t\r\n]+    /* eat up whitespace */
 \#[^\r\n]*    /* single-line comments */
diff --git a/src/libexpr/nixexpr-ast.def b/src/libexpr/nixexpr-ast.def
deleted file mode 100644
index 00b5f5a13..000000000
--- a/src/libexpr/nixexpr-ast.def
+++ /dev/null
@@ -1,97 +0,0 @@
-init initNixExprHelpers
-
-Pos | string int int | Pos |
-NoPos | | Pos |
-
-Function | Pattern Expr Pos | Expr |
-Assert | Expr Expr Pos | Expr |
-With | Expr Expr Pos | Expr |
-If | Expr Expr Expr | Expr |
-OpNot | Expr | Expr |
-OpEq | Expr Expr | Expr |
-OpNEq | Expr Expr | Expr |
-OpAnd | Expr Expr | Expr |
-OpOr | Expr Expr | Expr |
-OpImpl | Expr Expr | Expr |
-OpUpdate | Expr Expr | Expr |
-SubPath | Expr Expr | Expr |
-OpHasAttr | Expr string | Expr |
-OpPlus | Expr Expr | Expr |
-OpConcat | Expr Expr | Expr |
-ConcatStrings | ATermList | Expr |
-Call | Expr Expr | Expr |
-Select | Expr string | Expr |
-Var | string | Expr |
-Int | int | Expr |
-
-# Strings in the evaluator carry a so-called `context' (the ATermList)
-# which is a list of strings representing store paths.  This is to
-# allow users to write things like
-#
-#   "--with-freetype2-library=" + freetype + "/lib"
-#
-# where `freetype' is a derivation (or a source to be copied to the
-# store).  If we just concatenated the strings without keeping track
-# of the referenced store paths, then if the string is used as a
-# derivation attribute, the derivation will not have the correct
-# dependencies in its inputDrvs and inputSrcs.
-#
-# The semantics of the context is as follows: when a string with
-# context C is used as a derivation attribute, then the derivations in
-# C will be added to the inputDrvs of the derivation, and the other
-# store paths in C will be added to the inputSrcs of the derivations.
-#
-# For canonicity, the store paths should be in sorted order.
-Str | string ATermList | Expr |
-Str | string | Expr | ObsoleteStr
-
-# Internal to the parser, doesn't occur in ASTs.
-IndStr | string | Expr |
-
-# A path is a reference to a file system object that is to be copied
-# to the Nix store when used as a derivation attribute.  When it is
-# concatenated to a string (i.e., `str + path'), it is also copied and
-# the resulting store path is concatenated to the string (with the
-# store path in the context).  If a string or path is concatenated to
-# a path (i.e., `path + str' or `path + path'), the result is a new
-# path (if the right-hand side is a string, the context must be
-# empty).
-Path | string | Expr |
-
-List | ATermList | Expr |
-BlackHole | | Expr |
-Undefined | | Expr |
-Removed | | Expr |
-PrimOp | int ATermBlob ATermList | Expr |
-Attrs | ATermList | Expr |
-Closed | Expr | Expr |
-Rec | ATermList ATermList | Expr |
-Bool | ATermBool | Expr |
-Null | | Expr |
-
-Bind | string Expr Pos | ATerm |
-BindAttrPath | ATermList Expr Pos | ATerm | # desugared during parsing
-Bind | string Expr | ATerm | ObsoleteBind
-Inherit | Expr ATermList Pos | ATerm |
-
-Scope | | Expr |
-
-VarPat | string | Pattern |
-AttrsPat | ATermList ATermBool | Pattern | # bool = `...'
-AtPat | Pattern Pattern | Pattern |
-
-Formal | string DefaultValue | ATerm |
-
-DefaultValue | Expr | DefaultValue |
-NoDefaultValue | | DefaultValue |
-
-True | | ATermBool |
-False | | ATermBool |
-
-PrimOpDef | int ATermBlob | ATerm |
-
-AttrRHS | Expr Pos | ATerm |
-
-eTrue = makeBool(makeTrue())
-eFalse = makeBool(makeFalse())
-sOverrides = toATerm("__overrides")
diff --git a/src/libexpr/nixexpr.cc b/src/libexpr/nixexpr.cc
index 3675dccea..898fdb609 100644
--- a/src/libexpr/nixexpr.cc
+++ b/src/libexpr/nixexpr.cc
@@ -1,407 +1,325 @@
 #include "nixexpr.hh"
 #include "derivations.hh"
 #include "util.hh"
-#include "aterm.hh"
-
-#include "nixexpr-ast.hh"
-#include "nixexpr-ast.cc"
 
 #include <cstdlib>
 
 
 namespace nix {
-    
 
-string showPos(ATerm pos)
+
+/* Displaying abstract syntax trees. */
+
+std::ostream & operator << (std::ostream & str, Expr & e)
 {
-    ATerm path;
-    int line, column;
-    if (matchNoPos(pos)) return "undefined position";
-    if (!matchPos(pos, path, line, column))
-        throw badTerm("position expected", pos);
-    return (format("`%1%:%2%:%3%'") % aterm2String(path) % line % column).str();
+    e.show(str);
+    return str;
 }
-    
 
-ATerm bottomupRewrite(TermFun & f, ATerm e)
+void Expr::show(std::ostream & str)
 {
-    checkInterrupt();
-
-    if (ATgetType(e) == AT_APPL) {
-        AFun fun = ATgetAFun(e);
-        int arity = ATgetArity(fun);
-        ATerm args[arity];
-
-        for (int i = 0; i < arity; ++i)
-            args[i] = bottomupRewrite(f, ATgetArgument(e, i));
-        
-        e = (ATerm) ATmakeApplArray(fun, args);
-    }
-
-    else if (ATgetType(e) == AT_LIST) {
-        ATermList in = (ATermList) e;
-        ATermList out = ATempty;
-
-        for (ATermIterator i(in); i; ++i)
-            out = ATinsert(out, bottomupRewrite(f, *i));
-
-        e = (ATerm) ATreverse(out);
-    }
+    abort();
+}
 
-    return f(e);
+void ExprInt::show(std::ostream & str)
+{
+    str << n;
 }
 
+void ExprString::show(std::ostream & str)
+{
+    str << "\"" << s << "\""; // !!! escaping
+}
 
-void queryAllAttrs(Expr e, ATermMap & attrs, bool withPos)
+void ExprPath::show(std::ostream & str)
 {
-    ATermList bnds;
-    if (!matchAttrs(e, bnds))
-        throw TypeError(format("value is %1% while an attribute set was expected") % showType(e));
+    str << s;
+}
 
-    for (ATermIterator i(bnds); i; ++i) {
-        ATerm name;
-        Expr e;
-        ATerm pos;
-        if (!matchBind(*i, name, e, pos)) abort(); /* can't happen */
-        attrs.set(name, withPos ? makeAttrRHS(e, pos) : e);
-    }
+void ExprVar::show(std::ostream & str)
+{
+    str << info.name;
 }
 
+void ExprSelect::show(std::ostream & str)
+{
+    str << "(" << *e << ")." << name;
+}
 
-Expr queryAttr(Expr e, const string & name)
+void ExprOpHasAttr::show(std::ostream & str)
 {
-    ATerm dummy;
-    return queryAttr(e, name, dummy);
+    str << "(" << *e << ") ? " << name;
 }
 
+void ExprAttrs::show(std::ostream & str)
+{
+    if (recursive) str << "rec ";
+    str << "{ ";
+    foreach (list<Inherited>::iterator, i, inherited)
+        str << "inherit " << i->first.name << "; ";
+    foreach (Attrs::iterator, i, attrs)
+        str << i->first << " = " << *i->second.first << "; ";
+    str << "}";
+}
 
-Expr queryAttr(Expr e, const string & name, ATerm & pos)
+void ExprList::show(std::ostream & str)
 {
-    ATermList bnds;
-    if (!matchAttrs(e, bnds))
-        throw TypeError(format("value is %1% while an attribute set was expected") % showType(e));
+    str << "[ ";
+    foreach (vector<Expr *>::iterator, i, elems)
+        str << "(" << **i << ") ";
+    str << "]";
+}
 
-    for (ATermIterator i(bnds); i; ++i) {
-        ATerm name2, pos2;
-        Expr e;
-        if (!matchBind(*i, name2, e, pos2))
-            abort(); /* can't happen */
-        if (aterm2String(name2) == name) {
-            pos = pos2;
-            return e;
+void ExprLambda::show(std::ostream & str)
+{
+    str << "(";
+    if (matchAttrs) {
+        str << "{ ";
+        bool first = true;
+        foreach (Formals::Formals_::iterator, i, formals->formals) {
+            if (first) first = false; else str << ", ";
+            str << i->name;
+            if (i->def) str << " ? " << *i->def;
         }
+        str << " }";
+        if (!arg.empty()) str << " @ ";
     }
-
-    return 0;
+    if (!arg.empty()) str << arg;
+    str << ": " << *body << ")";
 }
 
-
-Expr makeAttrs(const ATermMap & attrs)
+void ExprLet::show(std::ostream & str)
 {
-    ATermList bnds = ATempty;
-    for (ATermMap::const_iterator i = attrs.begin(); i != attrs.end(); ++i) {
-        Expr e;
-        ATerm pos;
-        if (!matchAttrRHS(i->value, e, pos))
-            abort(); /* can't happen */
-        bnds = ATinsert(bnds, makeBind(i->key, e, pos));
-    }
-    return makeAttrs(bnds);
+    str << "let ";
+    foreach (list<ExprAttrs::Inherited>::iterator, i, attrs->inherited)
+        str << "inherit " << i->first.name << "; ";
+    foreach (ExprAttrs::Attrs::iterator, i, attrs->attrs)
+        str << i->first << " = " << *i->second.first << "; ";
+    str << "in " << *body;
 }
 
-
-static void varsBoundByPattern(ATermMap & map, Pattern pat)
+void ExprWith::show(std::ostream & str)
 {
-    ATerm name;
-    ATermList formals;
-    Pattern pat1, pat2;
-    ATermBool ellipsis;
-    /* Use makeRemoved() so that it can be used directly in
-       substitute(). */
-    if (matchVarPat(pat, name))
-        map.set(name, makeRemoved());
-    else if (matchAttrsPat(pat, formals, ellipsis)) { 
-        for (ATermIterator i(formals); i; ++i) {
-            ATerm d1;
-            if (!matchFormal(*i, name, d1)) abort();
-            map.set(name, makeRemoved());
-        }
-    }
-    else if (matchAtPat(pat, pat1, pat2)) {
-        varsBoundByPattern(map, pat1);
-        varsBoundByPattern(map, pat2);
-    }
-    else abort();
+    str << "with " << *attrs << "; " << *body;
 }
 
+void ExprIf::show(std::ostream & str)
+{
+    str << "if " << *cond << " then " << *then << " else " << *else_;
+}
 
-Expr substitute(const Substitution & subs, Expr e)
+void ExprAssert::show(std::ostream & str)
 {
-    checkInterrupt();
+    str << "assert " << *cond << "; " << *body;
+}
 
-    //if (subs.size() == 0) return e;
+void ExprOpNot::show(std::ostream & str)
+{
+    str << "! " << *e;
+}
 
-    ATerm name, pos, e2;
+void ExprConcatStrings::show(std::ostream & str)
+{
+    bool first = true;
+    foreach (vector<Expr *>::iterator, i, *es) {
+        if (first) first = false; else str << " + ";
+        str << **i;
+    }
+}
 
-    /* As an optimisation, don't substitute in subterms known to be
-       closed. */
-    if (matchClosed(e, e2)) return e;
 
-    if (matchVar(e, name)) {
-        Expr sub = subs.lookup(name);
-        if (sub == makeRemoved()) sub = 0;
-        Expr wrapped;
-        /* Add a "closed" wrapper around terms that aren't already
-           closed.  The check is necessary to prevent repeated
-           wrapping, e.g., closed(closed(closed(...))), which kills
-           caching. */
-        return sub ? (matchClosed(sub, wrapped) ? sub : makeClosed(sub)) : e;
-    }
+std::ostream & operator << (std::ostream & str, const Pos & pos)
+{
+    if (!pos.line)
+        str << "undefined position";
+    else
+        str << (format("`%1%:%2%:%3%'") % pos.file % pos.line % pos.column).str();
+    return str;
+}
 
-    /* In case of a function, filter out all variables bound by this
-       function. */
-    Pattern pat;
-    ATerm body;
-    if (matchFunction(e, pat, body, pos)) {
-        ATermMap map(16);
-        varsBoundByPattern(map, pat);
-        Substitution subs2(&subs, &map);
-        return makeFunction(
-            (Pattern) substitute(subs2, (Expr) pat),
-            substitute(subs2, body), pos);
-    }
 
-    /* Idem for a mutually recursive attribute set. */
-    ATermList rbnds, nrbnds;
-    if (matchRec(e, rbnds, nrbnds)) {
-        ATermMap map(ATgetLength(rbnds) + ATgetLength(nrbnds));
-        for (ATermIterator i(rbnds); i; ++i)
-            if (matchBind(*i, name, e2, pos)) map.set(name, makeRemoved());
-            else abort(); /* can't happen */
-        for (ATermIterator i(nrbnds); i; ++i)
-            if (matchBind(*i, name, e2, pos)) map.set(name, makeRemoved());
-            else abort(); /* can't happen */
-        return makeRec(
-            (ATermList) substitute(Substitution(&subs, &map), (ATerm) rbnds),
-            (ATermList) substitute(subs, (ATerm) nrbnds));
-    }
+Pos noPos;
 
-    if (ATgetType(e) == AT_APPL) {
-        AFun fun = ATgetAFun(e);
-        int arity = ATgetArity(fun);
-        ATerm args[arity];
-        bool changed = false;
 
-        for (int i = 0; i < arity; ++i) {
-            ATerm arg = ATgetArgument(e, i);
-            args[i] = substitute(subs, arg);
-            if (args[i] != arg) changed = true;
-        }
-        
-        return changed ? (ATerm) ATmakeApplArray(fun, args) : e;
-    }
+/* Computing levels/displacements for variables. */
 
-    if (ATgetType(e) == AT_LIST) {
-        unsigned int len = ATgetLength((ATermList) e);
-        ATerm es[len];
-        ATermIterator i((ATermList) e);
-        for (unsigned int j = 0; i; ++i, ++j)
-            es[j] = substitute(subs, *i);
-        ATermList out = ATempty;
-        for (unsigned int j = len; j; --j)
-            out = ATinsert(out, es[j - 1]);
-        return (ATerm) out;
-    }
+void Expr::bindVars(const StaticEnv & env)
+{
+    abort();
+}
 
-    return e;
+void ExprInt::bindVars(const StaticEnv & env)
+{
 }
 
+void ExprString::bindVars(const StaticEnv & env)
+{
+}
 
-/* We use memoisation to prevent exponential complexity on heavily
-   shared ATerms (remember, an ATerm is a graph, not a tree!).  Note
-   that using an STL set is fine here wrt to ATerm garbage collection
-   since all the ATerms in the set are already reachable from
-   somewhere else. */
-static void checkVarDefs2(set<Expr> & done, const ATermMap & defs, Expr e)
+void ExprPath::bindVars(const StaticEnv & env)
 {
-    if (done.find(e) != done.end()) return;
-    done.insert(e);
-    
-    ATerm name, pos, value;
-    ATerm with, body;
-    ATermList rbnds, nrbnds;
-    Pattern pat;
-
-    /* Closed terms don't have free variables, so we don't have to
-       check by definition. */
-    if (matchClosed(e, value)) return;
-    
-    else if (matchVar(e, name)) {
-        if (!defs.get(name))
-            throw EvalError(format("undefined variable `%1%'")
-                % aterm2String(name));
-    }
+}
 
-    else if (matchFunction(e, pat, body, pos)) {
-        ATermMap defs2(defs);
-        varsBoundByPattern(defs2, pat);
-        set<Expr> done2;
-        checkVarDefs2(done2, defs2, pat);
-        checkVarDefs2(done2, defs2, body);
-    }
-        
-    else if (matchRec(e, rbnds, nrbnds)) {
-        checkVarDefs2(done, defs, (ATerm) nrbnds);
-        ATermMap defs2(defs);
-        for (ATermIterator i(rbnds); i; ++i) {
-            if (!matchBind(*i, name, value, pos)) abort(); /* can't happen */
-            defs2.set(name, (ATerm) ATempty);
-        }
-        for (ATermIterator i(nrbnds); i; ++i) {
-            if (!matchBind(*i, name, value, pos)) abort(); /* can't happen */
-            defs2.set(name, (ATerm) ATempty);
+void VarRef::bind(const StaticEnv & env)
+{
+    /* Check whether the variable appears in the environment.  If so,
+       set its level and displacement. */
+    const StaticEnv * curEnv;
+    unsigned int level;
+    int withLevel = -1;
+    for (curEnv = &env, level = 0; curEnv; curEnv = curEnv->up, level++) {
+        if (curEnv->isWith) {
+            if (withLevel == -1) withLevel = level;
+        } else {
+            StaticEnv::Vars::const_iterator i = curEnv->vars.find(name);
+            if (i != curEnv->vars.end()) {
+                fromWith = false;
+                this->level = level;
+                displ = i->second;
+                return;
+            }
         }
-        set<Expr> done2;
-        checkVarDefs2(done2, defs2, (ATerm) rbnds);
     }
 
-    else if (matchWith(e, with, body, pos)) {
-        /* We can't check the body without evaluating the definitions
-           (which is an arbitrary expression), so we don't do that
-           here but only when actually evaluating the `with'. */
-        checkVarDefs2(done, defs, with);
-    }
-    
-    else if (ATgetType(e) == AT_APPL) {
-        int arity = ATgetArity(ATgetAFun(e));
-        for (int i = 0; i < arity; ++i)
-            checkVarDefs2(done, defs, ATgetArgument(e, i));
-    }
+    /* Otherwise, the variable must be obtained from the nearest
+       enclosing `with'.  If there is no `with', then we can issue an
+       "undefined variable" error now. */
+    if (withLevel == -1) throw EvalError(format("undefined variable `%1%'") % name);
 
-    else if (ATgetType(e) == AT_LIST)
-        for (ATermIterator i((ATermList) e); i; ++i)
-            checkVarDefs2(done, defs, *i);
+    fromWith = true;
+    this->level = withLevel;
 }
 
-
-void checkVarDefs(const ATermMap & defs, Expr e)
+void ExprVar::bindVars(const StaticEnv & env)
 {
-    set<Expr> done;
-    checkVarDefs2(done, defs, e);
+    info.bind(env);
 }
 
+void ExprSelect::bindVars(const StaticEnv & env)
+{
+    e->bindVars(env);
+}
 
-struct Canonicalise : TermFun
+void ExprOpHasAttr::bindVars(const StaticEnv & env)
 {
-    ATerm operator () (ATerm e)
-    {
-        /* Remove position info. */
-        ATerm path;
-        int line, column;
-        if (matchPos(e, path, line, column))
-            return makeNoPos();
+    e->bindVars(env);
+}
 
-        /* Sort attribute sets. */
-        ATermList _;
-        if (matchAttrs(e, _)) {
-            ATermMap attrs;
-            queryAllAttrs(e, attrs);
-            StringSet names;
-            for (ATermMap::const_iterator i = attrs.begin(); i != attrs.end(); ++i)
-                names.insert(aterm2String(i->key));
+void ExprAttrs::bindVars(const StaticEnv & env)
+{
+    if (recursive) {
+        StaticEnv newEnv(false, &env);
+    
+        unsigned int displ = 0;
 
-            ATermList attrs2 = ATempty;
-            for (StringSet::reverse_iterator i = names.rbegin(); i != names.rend(); ++i)
-                attrs2 = ATinsert(attrs2,
-                    makeBind(toATerm(*i), attrs.get(toATerm(*i)), makeNoPos()));
+        foreach (ExprAttrs::Attrs::iterator, i, attrs)
+            newEnv.vars[i->first] = displ++;
 
-            return makeAttrs(attrs2);
+        foreach (list<Inherited>::iterator, i, inherited) {
+            newEnv.vars[i->first.name] = displ++;
+            i->first.bind(env);
         }
-        
-        return e;
+
+        foreach (ExprAttrs::Attrs::iterator, i, attrs)
+            i->second.first->bindVars(newEnv);
     }
-};
 
+    else {
+        foreach (ExprAttrs::Attrs::iterator, i, attrs)
+            i->second.first->bindVars(env);
 
-Expr canonicaliseExpr(Expr e)
-{
-    Canonicalise canonicalise;
-    return bottomupRewrite(canonicalise, e);
+        foreach (list<Inherited>::iterator, i, inherited)
+            i->first.bind(env);
+    }
 }
 
-
-Expr makeBool(bool b)
+void ExprList::bindVars(const StaticEnv & env)
 {
-    return b ? eTrue : eFalse;
+    foreach (vector<Expr *>::iterator, i, elems)
+        (*i)->bindVars(env);
 }
 
-
-bool matchStr(Expr e, string & s, PathSet & context)
+void ExprLambda::bindVars(const StaticEnv & env)
 {
-    ATermList l;
-    ATerm s_;
-
-    if (!matchStr(e, s_, l)) return false;
+    StaticEnv newEnv(false, &env);
+    
+    unsigned int displ = 0;
+    
+    if (!arg.empty()) newEnv.vars[arg] = displ++;
 
-    s = aterm2String(s_);
+    if (matchAttrs) {
+        foreach (Formals::Formals_::iterator, i, formals->formals)
+            newEnv.vars[i->name] = displ++;
 
-    for (ATermIterator i(l); i; ++i)
-        context.insert(aterm2String(*i));
+        foreach (Formals::Formals_::iterator, i, formals->formals)
+            if (i->def) i->def->bindVars(newEnv);
+    }
 
-    return true;
+    body->bindVars(newEnv);
 }
 
+void ExprLet::bindVars(const StaticEnv & env)
+{
+    StaticEnv newEnv(false, &env);
+    
+    unsigned int displ = 0;
+
+    foreach (ExprAttrs::Attrs::iterator, i, attrs->attrs)
+        newEnv.vars[i->first] = displ++;
+
+    foreach (list<ExprAttrs::Inherited>::iterator, i, attrs->inherited) {
+        newEnv.vars[i->first.name] = displ++;
+        i->first.bind(env);
+    }
 
-Expr makeStr(const string & s, const PathSet & context)
+    foreach (ExprAttrs::Attrs::iterator, i, attrs->attrs)
+        i->second.first->bindVars(newEnv);
+    
+    body->bindVars(newEnv);
+}
+
+void ExprWith::bindVars(const StaticEnv & env)
 {
-    return makeStr(toATerm(s), toATermList(context));
+    /* Does this `with' have an enclosing `with'?  If so, record its
+       level so that `lookupVar' can look up variables in the previous
+       `with' if this one doesn't contain the desired attribute. */
+    const StaticEnv * curEnv;
+    unsigned int level;
+    prevWith = 0;
+    for (curEnv = &env, level = 1; curEnv; curEnv = curEnv->up, level++)
+        if (curEnv->isWith) {
+            prevWith = level;
+            break;
+        }
+    
+    attrs->bindVars(env);    
+    StaticEnv newEnv(true, &env);
+    body->bindVars(newEnv);
 }
 
+void ExprIf::bindVars(const StaticEnv & env)
+{
+    cond->bindVars(env);
+    then->bindVars(env);
+    else_->bindVars(env);
+}
 
-string showType(Expr e)
+void ExprAssert::bindVars(const StaticEnv & env)
 {
-    ATerm t1, t2;
-    ATermList l1;
-    ATermBlob b1;
-    int i1;
-    Pattern p1;
-    if (matchStr(e, t1, l1)) return "a string";
-    if (matchPath(e, t1)) return "a path";
-    if (matchNull(e)) return "null";
-    if (matchInt(e, i1)) return "an integer";
-    if (matchBool(e, t1)) return "a boolean";
-    if (matchFunction(e, p1, t1, t2)) return "a function";
-    if (matchAttrs(e, l1)) return "an attribute set";
-    if (matchList(e, l1)) return "a list";
-    if (matchPrimOp(e, i1, b1, l1)) return "a partially applied built-in function";
-    return "an unknown type";
+    cond->bindVars(env);
+    body->bindVars(env);
 }
 
+void ExprOpNot::bindVars(const StaticEnv & env)
+{
+    e->bindVars(env);
+}
 
-string showValue(Expr e)
+void ExprConcatStrings::bindVars(const StaticEnv & env)
 {
-    PathSet context;
-    string s;
-    ATerm s2;
-    int i;
-    if (matchStr(e, s, context)) {
-        string u;
-        for (string::iterator i = s.begin(); i != s.end(); ++i)
-            if (*i == '\"' || *i == '\\') u += "\\" + *i;
-            else if (*i == '\n') u += "\\n";
-            else if (*i == '\r') u += "\\r";
-            else if (*i == '\t') u += "\\t";
-            else u += *i;
-        return "\"" + u + "\"";
-    }
-    if (matchPath(e, s2)) return aterm2String(s2);
-    if (matchNull(e)) return "null";
-    if (matchInt(e, i)) return (format("%1%") % i).str();
-    if (e == eTrue) return "true";
-    if (e == eFalse) return "false";
-    /* !!! incomplete */
-    return "<unknown>";
+    foreach (vector<Expr *>::iterator, i, *es)
+        (*i)->bindVars(env);
 }
 
- 
+
 }
diff --git a/src/libexpr/nixexpr.hh b/src/libexpr/nixexpr.hh
index c7cdf46df..1c72441b2 100644
--- a/src/libexpr/nixexpr.hh
+++ b/src/libexpr/nixexpr.hh
@@ -3,8 +3,7 @@
 
 #include <map>
 
-#include "aterm-map.hh"
-#include "types.hh"
+#include "symbol-table.hh"
 
 
 namespace nix {
@@ -18,105 +17,254 @@ MakeError(Abort, EvalError)
 MakeError(TypeError, EvalError)
 
 
-/* Nix expressions are represented as ATerms.  The maximal sharing
-   property of the ATerm library allows us to implement caching of
-   normals forms efficiently. */
-typedef ATerm Expr;
-typedef ATerm DefaultValue;
-typedef ATerm Pos;
-typedef ATerm Pattern;
-typedef ATerm ATermBool;
+/* Position objects. */
 
+struct Pos
+{
+    string file;
+    unsigned int line, column;
+    Pos() : line(0), column(0) { };
+    Pos(const string & file, unsigned int line, unsigned int column)
+        : file(file), line(line), column(column) { };
+};
+
+extern Pos noPos;
+
+std::ostream & operator << (std::ostream & str, const Pos & pos);
 
-/* A STL vector of ATerms.  Should be used with great care since it's
-   stored on the heap, and the elements are therefore not roots to the
-   ATerm garbage collector. */
-typedef vector<ATerm> ATermVector;
 
+struct Env;
+struct Value;
+struct EvalState;
+struct StaticEnv;
 
-/* A substitution is a linked list of ATermMaps that map names to
-   identifiers.  We use a list of ATermMaps rather than a single to
-   make it easy to grow or shrink a substitution when entering a
-   scope. */
-struct Substitution
+
+/* Abstract syntax of Nix expressions. */
+
+struct Expr
 {
-    ATermMap * map;
-    const Substitution * prev;
+    virtual void show(std::ostream & str);
+    virtual void bindVars(const StaticEnv & env);
+    virtual void eval(EvalState & state, Env & env, Value & v);
+};
 
-    Substitution(const Substitution * prev, ATermMap * map)
-    {
-        this->prev = prev;
-        this->map = map;
-    }
-    
-    Expr lookup(Expr name) const
-    {
-        Expr x;
-        for (const Substitution * s(this); s; s = s->prev)
-            if ((x = s->map->get(name))) return x;
-        return 0;
-    }
+std::ostream & operator << (std::ostream & str, Expr & e);
+
+#define COMMON_METHODS \
+    void show(std::ostream & str); \
+    void eval(EvalState & state, Env & env, Value & v); \
+    void bindVars(const StaticEnv & env);
+
+struct ExprInt : Expr
+{
+    int n;
+    ExprInt(int n) : n(n) { };
+    COMMON_METHODS
 };
 
+struct ExprString : Expr
+{
+    string s;
+    ExprString(const string & s) : s(s) { };
+    COMMON_METHODS
+};
 
-/* Show a position. */
-string showPos(ATerm pos);
+/* Temporary class used during parsing of indented strings. */
+struct ExprIndStr : Expr
+{
+    string s;
+    ExprIndStr(const string & s) : s(s) { };
+};
 
-/* Generic bottomup traversal over ATerms.  The traversal first
-   recursively descends into subterms, and then applies the given term
-   function to the resulting term. */
-struct TermFun
+struct ExprPath : Expr
 {
-    virtual ~TermFun() { }
-    virtual ATerm operator () (ATerm e) = 0;
+    string s;
+    ExprPath(const string & s) : s(s) { };
+    COMMON_METHODS
 };
-ATerm bottomupRewrite(TermFun & f, ATerm e);
 
+struct VarRef
+{
+    Symbol name;
 
-/* Query all attributes in an attribute set expression.  The
-   expression must be in normal form. */
-void queryAllAttrs(Expr e, ATermMap & attrs, bool withPos = false);
+    /* Whether the variable comes from an environment (e.g. a rec, let
+       or function argument) or from a "with". */
+    bool fromWith;
+    
+    /* In the former case, the value is obtained by going `level'
+       levels up from the current environment and getting the
+       `displ'th value in that environment.  In the latter case, the
+       value is obtained by getting the attribute named `name' from
+       the attribute set stored in the environment that is `level'
+       levels up from the current one.*/
+    unsigned int level;
+    unsigned int displ;
+
+    VarRef(const Symbol & name) : name(name) { };
+    void bind(const StaticEnv & env);
+};
 
-/* Query a specific attribute from an attribute set expression.  The
-   expression must be in normal form. */
-Expr queryAttr(Expr e, const string & name);
-Expr queryAttr(Expr e, const string & name, ATerm & pos);
+struct ExprVar : Expr
+{
+    VarRef info;
+    ExprVar(const Symbol & name) : info(name) { };
+    COMMON_METHODS
+};
 
-/* Create an attribute set expression from an Attrs value. */
-Expr makeAttrs(const ATermMap & attrs);
+struct ExprSelect : Expr
+{
+    Expr * e;
+    Symbol name;
+    ExprSelect(Expr * e, const Symbol & name) : e(e), name(name) { };
+    COMMON_METHODS
+};
 
+struct ExprOpHasAttr : Expr
+{
+    Expr * e;
+    Symbol name;
+    ExprOpHasAttr(Expr * e, const Symbol & name) : e(e), name(name) { };
+    COMMON_METHODS
+};
 
-/* Perform a set of substitutions on an expression. */
-Expr substitute(const Substitution & subs, Expr e);
+struct ExprAttrs : Expr
+{
+    bool recursive;
+    typedef std::pair<Expr *, Pos> Attr;
+    typedef std::pair<VarRef, Pos> Inherited;
+    typedef std::map<Symbol, Attr> Attrs;
+    Attrs attrs;
+    list<Inherited> inherited;
+    std::map<Symbol, Pos> attrNames; // used during parsing
+    ExprAttrs() : recursive(false) { };
+    COMMON_METHODS
+};
 
+struct ExprList : Expr
+{
+    std::vector<Expr *> elems;
+    ExprList() { };
+    COMMON_METHODS
+};
 
-/* Check whether all variables are defined in the given expression.
-   Throw an exception if this isn't the case. */
-void checkVarDefs(const ATermMap & def, Expr e);
+struct Formal
+{
+    Symbol name;
+    Expr * def;
+    Formal(const Symbol & name, Expr * def) : name(name), def(def) { };
+};
 
+struct Formals
+{
+    typedef std::list<Formal> Formals_;
+    Formals_ formals;
+    std::set<Symbol> argNames; // used during parsing
+    bool ellipsis;
+};
+
+struct ExprLambda : Expr
+{
+    Pos pos;
+    Symbol arg;
+    bool matchAttrs;
+    Formals * formals;
+    Expr * body;
+    ExprLambda(const Pos & pos, const Symbol & arg, bool matchAttrs, Formals * formals, Expr * body)
+        : pos(pos), arg(arg), matchAttrs(matchAttrs), formals(formals), body(body)
+    {
+        if (!arg.empty() && formals && formals->argNames.find(arg) != formals->argNames.end())
+            throw ParseError(format("duplicate formal function argument `%1%' at %2%")
+                % arg % pos);
+    };
+    COMMON_METHODS
+};
+
+struct ExprLet : Expr
+{
+    ExprAttrs * attrs;
+    Expr * body;
+    ExprLet(ExprAttrs * attrs, Expr * body) : attrs(attrs), body(body) { };
+    COMMON_METHODS
+};
 
-/* Canonicalise a Nix expression by sorting attributes and removing
-   location information. */
-Expr canonicaliseExpr(Expr e);
+struct ExprWith : Expr
+{
+    Pos pos;
+    Expr * attrs, * body;
+    unsigned int prevWith;
+    ExprWith(const Pos & pos, Expr * attrs, Expr * body) : pos(pos), attrs(attrs), body(body) { };
+    COMMON_METHODS
+};
 
+struct ExprIf : Expr
+{
+    Expr * cond, * then, * else_;
+    ExprIf(Expr * cond, Expr * then, Expr * else_) : cond(cond), then(then), else_(else_) { };
+    COMMON_METHODS
+};
 
-/* Create an expression representing a boolean. */
-Expr makeBool(bool b);
+struct ExprAssert : Expr
+{
+    Pos pos;
+    Expr * cond, * body;
+    ExprAssert(const Pos & pos, Expr * cond, Expr * body) : pos(pos), cond(cond), body(body) { };
+    COMMON_METHODS
+};
 
+struct ExprOpNot : Expr
+{
+    Expr * e;
+    ExprOpNot(Expr * e) : e(e) { };
+    COMMON_METHODS
+};
 
-/* Manipulation of Str() nodes.  Note: matchStr() does not clear
-   context!  */
-bool matchStr(Expr e, string & s, PathSet & context);
+#define MakeBinOp(name, s) \
+    struct Expr##name : Expr \
+    { \
+        Expr * e1, * e2; \
+        Expr##name(Expr * e1, Expr * e2) : e1(e1), e2(e2) { }; \
+        void show(std::ostream & str) \
+        { \
+            str << *e1 << " " s " " << *e2; \
+        } \
+        void bindVars(const StaticEnv & env) \
+        { \
+            e1->bindVars(env); e2->bindVars(env); \
+        } \
+        void eval(EvalState & state, Env & env, Value & v); \
+    };
+
+MakeBinOp(App, "")
+MakeBinOp(OpEq, "==")
+MakeBinOp(OpNEq, "!=")
+MakeBinOp(OpAnd, "&&")
+MakeBinOp(OpOr, "||")
+MakeBinOp(OpImpl, "->")
+MakeBinOp(OpUpdate, "//")
+MakeBinOp(OpConcatLists, "++")
+
+struct ExprConcatStrings : Expr
+{
+    vector<Expr *> * es;
+    ExprConcatStrings(vector<Expr *> * es) : es(es) { };
+    COMMON_METHODS
+};
 
-Expr makeStr(const string & s, const PathSet & context = PathSet());
 
+/* Static environments are used to map variable names onto (level,
+   displacement) pairs used to obtain the value of the variable at
+   runtime. */
+struct StaticEnv
+{
+    bool isWith;
+    const StaticEnv * up;
+    typedef std::map<Symbol, unsigned int> Vars;
+    Vars vars;
+    StaticEnv(bool isWith, const StaticEnv * up) : isWith(isWith), up(up) { };
+};
 
-/* Showing types, values. */
-string showType(Expr e);
 
-string showValue(Expr e);
 
- 
 }
 
 
diff --git a/src/libexpr/parser.hh b/src/libexpr/parser.hh
index 334822b5e..c8c8ad809 100644
--- a/src/libexpr/parser.hh
+++ b/src/libexpr/parser.hh
@@ -8,12 +8,11 @@ namespace nix {
 
 
 /* Parse a Nix expression from the specified file.  If `path' refers
-   to a directory, the "/default.nix" is appended. */
-Expr parseExprFromFile(EvalState & state, Path path);
+   to a directory, then "/default.nix" is appended. */
+Expr * parseExprFromFile(EvalState & state, Path path);
 
 /* Parse a Nix expression from the specified string. */
-Expr parseExprFromString(EvalState & state, const string & s,
-    const Path & basePath);
+Expr * parseExprFromString(EvalState & state, const string & s, const Path & basePath);
 
 
 }
diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index 8706ce025..7236bab19 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -20,16 +20,14 @@
 #include <stdlib.h>
 #include <string.h>
 
-#include "aterm.hh"
 #include "util.hh"
     
+#include "nixexpr.hh"
+
 #include "parser-tab.hh"
 #include "lexer-tab.hh"
 #define YYSTYPE YYSTYPE // workaround a bug in Bison 2.4
 
-#include "nixexpr.hh"
-#include "nixexpr-ast.hh"
-
 
 using namespace nix;
 
@@ -39,145 +37,85 @@ namespace nix {
     
 struct ParseData 
 {
-    Expr result;
+    SymbolTable & symbols;
+    Expr * result;
     Path basePath;
     Path path;
     string error;
+    Symbol sLetBody;
+    ParseData(SymbolTable & symbols)
+        : symbols(symbols)
+        , sLetBody(symbols.create("<let-body>"))
+    { };
 };
- 
 
-static string showAttrPath(ATermList attrPath)
+
+static string showAttrPath(const vector<Symbol> & attrPath)
 {
     string s;
-    for (ATermIterator i(attrPath); i; ++i) {
+    foreach (vector<Symbol>::const_iterator, i, attrPath) {
         if (!s.empty()) s += '.';
-        s += aterm2String(*i);
+        s += *i;
     }
     return s;
 }
- 
-
-struct Tree
-{
-    Expr leaf; ATerm pos; bool recursive;
-    typedef std::map<ATerm, Tree> Children;
-    Children children;
-    Tree() { leaf = 0; recursive = true; }
-};
 
 
-static ATermList buildAttrs(const Tree & t, ATermList & nonrec)
+static void dupAttr(const vector<Symbol> & attrPath, const Pos & pos, const Pos & prevPos)
 {
-    ATermList res = ATempty;
-    for (Tree::Children::const_reverse_iterator i = t.children.rbegin();
-         i != t.children.rend(); ++i)
-        if (!i->second.recursive)
-            nonrec = ATinsert(nonrec, makeBind(i->first, i->second.leaf, i->second.pos));
-        else
-            res = ATinsert(res, i->second.leaf
-                ? makeBind(i->first, i->second.leaf, i->second.pos)
-                : makeBind(i->first, makeAttrs(buildAttrs(i->second, nonrec)), makeNoPos()));
-    return res;
+    throw ParseError(format("attribute `%1%' at %2% already defined at %3%")
+        % showAttrPath(attrPath) % pos % prevPos);
 }
  
 
-static Expr fixAttrs(bool recursive, ATermList as)
+static void dupAttr(Symbol attr, const Pos & pos, const Pos & prevPos)
 {
-    Tree attrs;
-
-    /* This ATermMap is needed to ensure that the `leaf' fields in the
-       Tree nodes are not garbage collected. */
-    ATermMap gcRoots;
-
-    for (ATermIterator i(as); i; ++i) {
-        ATermList names, attrPath; Expr src, e; ATerm name, pos;
-
-        if (matchInherit(*i, src, names, pos)) {
-            bool fromScope = matchScope(src);
-            for (ATermIterator j(names); j; ++j) {
-                if (attrs.children.find(*j) != attrs.children.end()) 
-                    throw ParseError(format("duplicate definition of attribute `%1%' at %2%")
-                        % showAttrPath(ATmakeList1(*j)) % showPos(pos));
-                Tree & t(attrs.children[*j]);
-                Expr leaf = fromScope ? makeVar(*j) : makeSelect(src, *j);
-                gcRoots.set(leaf, leaf);
-                t.leaf = leaf;
-                t.pos = pos;
-                if (recursive && fromScope) t.recursive = false;
-            }
-        }
-
-        else if (matchBindAttrPath(*i, attrPath, e, pos)) {
-
-            Tree * t(&attrs);
-            
-            for (ATermIterator j(attrPath); j; ) {
-                name = *j; ++j;
-                if (t->leaf) throw ParseError(format("attribute set containing `%1%' at %2% already defined at %3%")
-                    % showAttrPath(attrPath) % showPos(pos) % showPos (t->pos));
-                t = &(t->children[name]);
-            }
-
-            if (t->leaf)
-                throw ParseError(format("duplicate definition of attribute `%1%' at %2% and %3%")
-                    % showAttrPath(attrPath) % showPos(pos) % showPos (t->pos));
-            if (!t->children.empty())
-                throw ParseError(format("duplicate definition of attribute `%1%' at %2%")
-                    % showAttrPath(attrPath) % showPos(pos));
-
-            t->leaf = e; t->pos = pos;
-        }
-
-        else abort(); /* can't happen */
-    }
-
-    ATermList nonrec = ATempty;
-    ATermList rec = buildAttrs(attrs, nonrec);
-        
-    return recursive ? makeRec(rec, nonrec) : makeAttrs(rec);
+    vector<Symbol> attrPath; attrPath.push_back(attr);
+    throw ParseError(format("attribute `%1%' at %2% already defined at %3%")
+        % showAttrPath(attrPath) % pos % prevPos);
 }
+ 
 
-
-static void checkPatternVars(ATerm pos, ATermMap & map, Pattern pat)
+static void addAttr(ExprAttrs * attrs, const vector<Symbol> & attrPath,
+    Expr * e, const Pos & pos)
 {
-    ATerm name;
-    ATermList formals;
-    Pattern pat1, pat2;
-    ATermBool ellipsis;
-    if (matchVarPat(pat, name)) {
-        if (map.get(name))
-            throw ParseError(format("duplicate formal function argument `%1%' at %2%")
-                % aterm2String(name) % showPos(pos));
-        map.set(name, name);
-    }
-    else if (matchAttrsPat(pat, formals, ellipsis)) { 
-        for (ATermIterator i(formals); i; ++i) {
-            ATerm d1;
-            if (!matchFormal(*i, name, d1)) abort();
-            if (map.get(name))
-                throw ParseError(format("duplicate formal function argument `%1%' at %2%")
-                    % aterm2String(name) % showPos(pos));
-            map.set(name, name);
+    unsigned int n = 0;
+    foreach (vector<Symbol>::const_iterator, i, attrPath) {
+        n++;
+        ExprAttrs::Attrs::iterator j = attrs->attrs.find(*i);
+        if (j != attrs->attrs.end()) {
+            ExprAttrs * attrs2 = dynamic_cast<ExprAttrs *>(j->second.first);
+            if (!attrs2 || n == attrPath.size()) dupAttr(attrPath, pos, j->second.second);
+            attrs = attrs2;
+        } else {
+            if (attrs->attrNames.find(*i) != attrs->attrNames.end())
+                dupAttr(attrPath, pos, attrs->attrNames[*i]);
+            attrs->attrNames[*i] = pos;
+            if (n == attrPath.size())
+                attrs->attrs[*i] = ExprAttrs::Attr(e, pos);
+            else {
+                ExprAttrs * nested = new ExprAttrs;
+                attrs->attrs[*i] = ExprAttrs::Attr(nested, pos);
+                attrs = nested;
+            }
         }
     }
-    else if (matchAtPat(pat, pat1, pat2)) {
-        checkPatternVars(pos, map, pat1);
-        checkPatternVars(pos, map, pat2);
-    }
-    else abort();
 }
 
 
-static void checkPatternVars(ATerm pos, Pattern pat)
+static void addFormal(const Pos & pos, Formals * formals, const Formal & formal)
 {
-    ATermMap map;
-    checkPatternVars(pos, map, pat);
+    if (formals->argNames.find(formal.name) != formals->argNames.end())
+        throw ParseError(format("duplicate formal function argument `%1%' at %2%")
+            % formal.name % pos);
+    formals->formals.push_front(formal);
+    formals->argNames.insert(formal.name);
 }
 
 
-static Expr stripIndentation(ATermList es)
+static Expr * stripIndentation(vector<Expr *> & es)
 {
-    if (es == ATempty) return makeStr("");
+    if (es.empty()) return new ExprString("");
     
     /* Figure out the minimum indentation.  Note that by design
        whitespace-only final lines are not taken into account.  (So
@@ -185,9 +123,9 @@ static Expr stripIndentation(ATermList es)
     bool atStartOfLine = true; /* = seen only whitespace in the current line */
     unsigned int minIndent = 1000000;
     unsigned int curIndent = 0;
-    ATerm e;
-    for (ATermIterator i(es); i; ++i) {
-        if (!matchIndStr(*i, e)) {
+    foreach (vector<Expr *>::iterator, i, es) {
+        ExprIndStr * e = dynamic_cast<ExprIndStr *>(*i);
+        if (!e) {
             /* Anti-quotations end the current start-of-line whitespace. */
             if (atStartOfLine) {
                 atStartOfLine = false;
@@ -195,12 +133,11 @@ static Expr stripIndentation(ATermList es)
             }
             continue;
         }
-        string s = aterm2String(e);
-        for (unsigned int j = 0; j < s.size(); ++j) {
+        for (unsigned int j = 0; j < e->s.size(); ++j) {
             if (atStartOfLine) {
-                if (s[j] == ' ')
+                if (e->s[j] == ' ')
                     curIndent++;
-                else if (s[j] == '\n') {
+                else if (e->s[j] == '\n') {
                     /* Empty line, doesn't influence minimum
                        indentation. */
                     curIndent = 0;
@@ -208,7 +145,7 @@ static Expr stripIndentation(ATermList es)
                     atStartOfLine = false;
                     if (curIndent < minIndent) minIndent = curIndent;
                 }
-            } else if (s[j] == '\n') {
+            } else if (e->s[j] == '\n') {
                 atStartOfLine = true;
                 curIndent = 0;
             }
@@ -216,37 +153,37 @@ static Expr stripIndentation(ATermList es)
     }
 
     /* Strip spaces from each line. */
-    ATermList es2 = ATempty;
+    vector<Expr *> * es2 = new vector<Expr *>;
     atStartOfLine = true;
     unsigned int curDropped = 0;
-    unsigned int n = ATgetLength(es);
-    for (ATermIterator i(es); i; ++i, --n) {
-        if (!matchIndStr(*i, e)) {
+    unsigned int n = es.size();
+    for (vector<Expr *>::iterator i = es.begin(); i != es.end(); ++i, --n) {
+        ExprIndStr * e = dynamic_cast<ExprIndStr *>(*i);
+        if (!e) {
             atStartOfLine = false;
             curDropped = 0;
-            es2 = ATinsert(es2, *i);
+            es2->push_back(*i);
             continue;
         }
         
-        string s = aterm2String(e);
         string s2;
-        for (unsigned int j = 0; j < s.size(); ++j) {
+        for (unsigned int j = 0; j < e->s.size(); ++j) {
             if (atStartOfLine) {
-                if (s[j] == ' ') {
+                if (e->s[j] == ' ') {
                     if (curDropped++ >= minIndent)
-                        s2 += s[j];
+                        s2 += e->s[j];
                 }
-                else if (s[j] == '\n') {
+                else if (e->s[j] == '\n') {
                     curDropped = 0;
-                    s2 += s[j];
+                    s2 += e->s[j];
                 } else {
                     atStartOfLine = false;
                     curDropped = 0;
-                    s2 += s[j];
+                    s2 += e->s[j];
                 }
             } else {
-                s2 += s[j];
-                if (s[j] == '\n') atStartOfLine = true;
+                s2 += e->s[j];
+                if (e->s[j] == '\n') atStartOfLine = true;
             }
         }
 
@@ -257,11 +194,11 @@ static Expr stripIndentation(ATermList es)
             if (p != string::npos && s2.find_first_not_of(' ', p + 1) == string::npos)
                 s2 = string(s2, 0, p + 1);
         }
-            
-        es2 = ATinsert(es2, makeStr(s2));
+
+        es2->push_back(new ExprString(s2));
     }
 
-    return makeConcatStrings(ATreverse(es2));
+    return new ExprConcatStrings(es2);
 }
 
 
@@ -269,13 +206,12 @@ void backToString(yyscan_t scanner);
 void backToIndString(yyscan_t scanner);
 
 
-static Pos makeCurPos(YYLTYPE * loc, ParseData * data)
+static Pos makeCurPos(const YYLTYPE & loc, ParseData * data)
 {
-    return makePos(toATerm(data->path),
-        loc->first_line, loc->first_column);
+    return Pos(data->path, loc.first_line, loc.first_column);
 }
 
-#define CUR_POS makeCurPos(yylocp, data)
+#define CUR_POS makeCurPos(*yylocp, data)
 
 
 }
@@ -283,29 +219,10 @@ static Pos makeCurPos(YYLTYPE * loc, ParseData * data)
 
 void yyerror(YYLTYPE * loc, yyscan_t scanner, ParseData * data, const char * error)
 {
-    data->error = (format("%1%, at `%2%':%3%:%4%")
-        % error % data->path % loc->first_line % loc->first_column).str();
-}
-
-
-/* Make sure that the parse stack is scanned by the ATerm garbage
-   collector. */
-static void * mallocAndProtect(size_t size)
-{
-    void * p = malloc(size);
-    if (p) ATprotectMemory(p, size);
-    return p;
-}
-
-static void freeAndUnprotect(void * p)
-{
-    ATunprotectMemory(p);
-    free(p);
+    data->error = (format("%1%, at %2%")
+        % error % makeCurPos(*loc, data)).str();
 }
 
-#define YYMALLOC mallocAndProtect
-#define YYFREE freeAndUnprotect
-
 
 #endif
 
@@ -313,20 +230,32 @@ static void freeAndUnprotect(void * p)
 %}
 
 %union {
-  ATerm t;
-  ATermList ts;
-  struct {
-    ATermList formals;
-    bool ellipsis;
-  } formals;
+  nix::Expr * e;
+  nix::ExprList * list;
+  nix::ExprAttrs * attrs;
+  nix::Formals * formals;
+  nix::Formal * formal;
+  int n;
+  char * id; // !!! -> Symbol
+  char * path;
+  char * uri;
+  std::vector<nix::Symbol> * ids;
+  std::vector<nix::Expr *> * string_parts;
 }
 
-%type <t> start expr expr_function expr_if expr_op
-%type <t> expr_app expr_select expr_simple bind inheritsrc formal
-%type <t> pattern pattern2
-%type <ts> binds ids attrpath expr_list string_parts ind_string_parts
+%type <e> start expr expr_function expr_if expr_op
+%type <e> expr_app expr_select expr_simple
+%type <list> expr_list
+%type <attrs> binds
 %type <formals> formals
-%token <t> ID INT STR IND_STR PATH URI
+%type <formal> formal
+%type <ids> ids attrpath
+%type <string_parts> string_parts ind_string_parts
+%token <id> ID ATTRPATH
+%token <e> STR IND_STR
+%token <n> INT
+%token <path> PATH
+%token <uri> URI
 %token IF THEN ELSE ASSERT WITH LET IN REC INHERIT EQ NEQ AND OR IMPL
 %token DOLLAR_CURLY /* == ${ */
 %token IND_STRING_OPEN IND_STRING_CLOSE
@@ -350,163 +279,172 @@ start: expr { data->result = $1; };
 expr: expr_function;
 
 expr_function
-  : pattern ':' expr_function
-    { checkPatternVars(CUR_POS, $1); $$ = makeFunction($1, $3, CUR_POS); }
+  : ID ':' expr_function
+    { $$ = new ExprLambda(CUR_POS, data->symbols.create($1), false, 0, $3); }
+  | '{' formals '}' ':' expr_function
+    { $$ = new ExprLambda(CUR_POS, data->symbols.create(""), true, $2, $5); }
+  | '{' formals '}' '@' ID ':' expr_function
+    { $$ = new ExprLambda(CUR_POS, data->symbols.create($5), true, $2, $7); }
+  | ID '@' '{' formals '}' ':' expr_function
+    { $$ = new ExprLambda(CUR_POS, data->symbols.create($1), true, $4, $7); }
   | ASSERT expr ';' expr_function
-    { $$ = makeAssert($2, $4, CUR_POS); }
+    { $$ = new ExprAssert(CUR_POS, $2, $4); }
   | WITH expr ';' expr_function
-    { $$ = makeWith($2, $4, CUR_POS); }
+    { $$ = new ExprWith(CUR_POS, $2, $4); }
   | LET binds IN expr_function
-    { $$ = makeSelect(fixAttrs(true, ATinsert($2, makeBindAttrPath(ATmakeList1(toATerm("<let-body>")), $4, CUR_POS))), toATerm("<let-body>")); }
+    { $$ = new ExprLet($2, $4); }
   | expr_if
   ;
 
 expr_if
-  : IF expr THEN expr ELSE expr
-    { $$ = makeIf($2, $4, $6); }
+  : IF expr THEN expr ELSE expr { $$ = new ExprIf($2, $4, $6); }
   | expr_op
   ;
 
 expr_op
-  : '!' expr_op %prec NEG { $$ = makeOpNot($2); }
-  | expr_op EQ expr_op { $$ = makeOpEq($1, $3); }
-  | expr_op NEQ expr_op { $$ = makeOpNEq($1, $3); }
-  | expr_op AND expr_op { $$ = makeOpAnd($1, $3); }
-  | expr_op OR expr_op { $$ = makeOpOr($1, $3); }
-  | expr_op IMPL expr_op { $$ = makeOpImpl($1, $3); }
-  | expr_op UPDATE expr_op { $$ = makeOpUpdate($1, $3); }
-  | expr_op '~' expr_op { $$ = makeSubPath($1, $3); }
-  | expr_op '?' ID { $$ = makeOpHasAttr($1, $3); }
-  | expr_op '+' expr_op { $$ = makeOpPlus($1, $3); }
-  | expr_op CONCAT expr_op { $$ = makeOpConcat($1, $3); }
+  : '!' expr_op %prec NEG { $$ = new ExprOpNot($2); }
+  | expr_op EQ expr_op { $$ = new ExprOpEq($1, $3); }
+  | expr_op NEQ expr_op { $$ = new ExprOpNEq($1, $3); }
+  | expr_op AND expr_op { $$ = new ExprOpAnd($1, $3); }
+  | expr_op OR expr_op { $$ = new ExprOpOr($1, $3); }
+  | expr_op IMPL expr_op { $$ = new ExprOpImpl($1, $3); }
+  | expr_op UPDATE expr_op { $$ = new ExprOpUpdate($1, $3); }
+  | expr_op '?' ID { $$ = new ExprOpHasAttr($1, data->symbols.create($3)); }
+  | expr_op '+' expr_op
+    { vector<Expr *> * l = new vector<Expr *>;
+      l->push_back($1);
+      l->push_back($3);
+      $$ = new ExprConcatStrings(l);
+    }
+  | expr_op CONCAT expr_op { $$ = new ExprOpConcatLists($1, $3); }
   | expr_app
   ;
 
 expr_app
   : expr_app expr_select
-    { $$ = makeCall($1, $2); }
+    { $$ = new ExprApp($1, $2); }
   | expr_select { $$ = $1; }
   ;
 
 expr_select
   : expr_select '.' ID
-    { $$ = makeSelect($1, $3); }
+    { $$ = new ExprSelect($1, data->symbols.create($3)); }
   | expr_simple { $$ = $1; }
   ;
 
 expr_simple
-  : ID { $$ = makeVar($1); }
-  | INT { $$ = makeInt(ATgetInt((ATermInt) $1)); }
+  : ID { $$ = new ExprVar(data->symbols.create($1)); }
+  | INT { $$ = new ExprInt($1); }
   | '"' string_parts '"' {
       /* For efficiency, and to simplify parse trees a bit. */
-      if ($2 == ATempty) $$ = makeStr(toATerm(""), ATempty);
-      else if (ATgetNext($2) == ATempty) $$ = ATgetFirst($2);
-      else $$ = makeConcatStrings(ATreverse($2));
+      if ($2->empty()) $$ = new ExprString("");
+      else if ($2->size() == 1) $$ = $2->front();
+      else $$ = new ExprConcatStrings($2);
   }
   | IND_STRING_OPEN ind_string_parts IND_STRING_CLOSE {
-      $$ = stripIndentation(ATreverse($2));
+      $$ = stripIndentation(*$2);
   }
-  | PATH { $$ = makePath(toATerm(absPath(aterm2String($1), data->basePath))); }
-  | URI { $$ = makeStr($1, ATempty); }
+  | PATH { $$ = new ExprPath(absPath($1, data->basePath)); }
+  | URI { $$ = new ExprString($1); }
   | '(' expr ')' { $$ = $2; }
   /* Let expressions `let {..., body = ...}' are just desugared
      into `(rec {..., body = ...}).body'. */
   | LET '{' binds '}'
-    { $$ = makeSelect(fixAttrs(true, $3), toATerm("body")); }
+    { $3->recursive = true; $$ = new ExprSelect($3, data->symbols.create("body")); }
   | REC '{' binds '}'
-    { $$ = fixAttrs(true, $3); }
+    { $3->recursive = true; $$ = $3; }
   | '{' binds '}'
-    { $$ = fixAttrs(false, $2); }
-  | '[' expr_list ']' { $$ = makeList(ATreverse($2)); }
+    { $$ = $2; }
+  | '[' expr_list ']' { $$ = $2; }
   ;
 
 string_parts
-  : string_parts STR { $$ = ATinsert($1, $2); }
-  | string_parts DOLLAR_CURLY expr '}' { backToString(scanner); $$ = ATinsert($1, $3); }
-  | { $$ = ATempty; }
+  : string_parts STR { $$ = $1; $1->push_back($2); }
+  | string_parts DOLLAR_CURLY expr '}' { backToString(scanner); $$ = $1; $1->push_back($3); }
+  | { $$ = new vector<Expr *>; }
   ;
 
 ind_string_parts
-  : ind_string_parts IND_STR { $$ = ATinsert($1, $2); }
-  | ind_string_parts DOLLAR_CURLY expr '}' { backToIndString(scanner); $$ = ATinsert($1, $3); }
-  | { $$ = ATempty; }
-  ;
-
-pattern
-  : pattern2 '@' pattern { $$ = makeAtPat($1, $3); }
-  | pattern2
-  ;
-
-pattern2
-  : ID { $$ = makeVarPat($1); }
-  | '{' formals '}' { $$ = makeAttrsPat($2.formals, $2.ellipsis ? eTrue : eFalse); }
+  : ind_string_parts IND_STR { $$ = $1; $1->push_back($2); }
+  | ind_string_parts DOLLAR_CURLY expr '}' { backToIndString(scanner); $$ = $1; $1->push_back($3); }
+  | { $$ = new vector<Expr *>; }
   ;
 
 binds
-  : binds bind { $$ = ATinsert($1, $2); }
-  | { $$ = ATempty; }
-  ;
-
-bind
-  : attrpath '=' expr ';'
-    { $$ = makeBindAttrPath(ATreverse($1), $3, CUR_POS); }
-  | INHERIT inheritsrc ids ';'
-    { $$ = makeInherit($2, $3, CUR_POS); }
+  : binds attrpath '=' expr ';' { $$ = $1; addAttr($$, *$2, $4, makeCurPos(@2, data)); }
+  | binds INHERIT ids ';'
+    { $$ = $1;
+      foreach (vector<Symbol>::iterator, i, *$3) {
+          if ($$->attrNames.find(*i) != $$->attrNames.end())
+              dupAttr(*i, makeCurPos(@3, data), $$->attrNames[*i]);
+          Pos pos = makeCurPos(@3, data);
+          $$->inherited.push_back(ExprAttrs::Inherited(*i, pos));
+          $$->attrNames[*i] = pos;
+      }
+    }
+  | binds INHERIT '(' expr ')' ids ';'
+    { $$ = $1;
+      /* !!! Should ensure sharing of the expression in $4. */
+      foreach (vector<Symbol>::iterator, i, *$6) {
+          if ($$->attrNames.find(*i) != $$->attrNames.end())
+              dupAttr(*i, makeCurPos(@6, data), $$->attrNames[*i]);
+          $$->attrs[*i] = ExprAttrs::Attr(new ExprSelect($4, *i), makeCurPos(@6, data));
+          $$->attrNames[*i] = makeCurPos(@6, data);
+      }}
+
+  | { $$ = new ExprAttrs; }
   ;
 
-inheritsrc
-  : '(' expr ')' { $$ = $2; }
-  | { $$ = makeScope(); }
+ids
+  : ids ID { $$ = $1; $1->push_back(data->symbols.create($2)); /* !!! dangerous */ }
+  | { $$ = new vector<Symbol>; }
   ;
 
-ids: ids ID { $$ = ATinsert($1, $2); } | { $$ = ATempty; };
-
 attrpath
-  : attrpath '.' ID { $$ = ATinsert($1, $3); }
-  | ID { $$ = ATmakeList1($1); }
+  : attrpath '.' ID { $$ = $1; $1->push_back(data->symbols.create($3)); }
+  | ID { $$ = new vector<Symbol>; $$->push_back(data->symbols.create($1)); }
   ;
 
 expr_list
-  : expr_list expr_select { $$ = ATinsert($1, $2); }
-  | { $$ = ATempty; }
+  : expr_list expr_select { $$ = $1; $1->elems.push_back($2); /* !!! dangerous */ }
+  | { $$ = new ExprList; }
   ;
 
 formals
-  : formal ',' formals /* !!! right recursive */
-    { $$.formals = ATinsert($3.formals, $1); $$.ellipsis = $3.ellipsis; }
+  : formal ',' formals
+    { $$ = $3; addFormal(CUR_POS, $$, *$1); }
   | formal
-    { $$.formals = ATinsert(ATempty, $1); $$.ellipsis = false; }
+    { $$ = new Formals; addFormal(CUR_POS, $$, *$1); $$->ellipsis = false; }
   |
-    { $$.formals = ATempty; $$.ellipsis = false; }
+    { $$ = new Formals; $$->ellipsis = false; }
   | ELLIPSIS
-    { $$.formals = ATempty; $$.ellipsis = true; }
+    { $$ = new Formals; $$->ellipsis = true; }
   ;
 
 formal
-  : ID { $$ = makeFormal($1, makeNoDefaultValue()); }
-  | ID '?' expr { $$ = makeFormal($1, makeDefaultValue($3)); }
+  : ID { $$ = new Formal(data->symbols.create($1), 0); }
+  | ID '?' expr { $$ = new Formal(data->symbols.create($1), $3); }
   ;
   
 %%
 
 
-#include "eval.hh"  
-
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <unistd.h>
 
+#include <eval.hh>
+
 
 namespace nix {
       
 
-static Expr parse(EvalState & state,
-    const char * text, const Path & path,
-    const Path & basePath)
+static Expr * parse(EvalState & state, const char * text,
+    const Path & path, const Path & basePath)
 {
     yyscan_t scanner;
-    ParseData data;
+    ParseData data(state.symbols);
     data.basePath = basePath;
     data.path = path;
 
@@ -518,7 +456,7 @@ static Expr parse(EvalState & state,
     if (res) throw ParseError(data.error);
 
     try {
-        checkVarDefs(state.primOps, data.result);
+        data.result->bindVars(state.staticBaseEnv);
     } catch (Error & e) {
         throw ParseError(format("%1%, in `%2%'") % e.msg() % path);
     }
@@ -527,16 +465,10 @@ static Expr parse(EvalState & state,
 }
 
 
-Expr parseExprFromFile(EvalState & state, Path path)
+Expr * parseExprFromFile(EvalState & state, Path path)
 {
     assert(path[0] == '/');
 
-#if 0
-    /* Perhaps this is already an imploded parse tree? */
-    Expr e = ATreadFromNamedFile(path.c_str());
-    if (e) return e;
-#endif
-
     /* If `path' is a symlink, follow it.  This is so that relative
        path references work. */
     struct stat st;
@@ -558,7 +490,7 @@ Expr parseExprFromFile(EvalState & state, Path path)
 }
 
 
-Expr parseExprFromString(EvalState & state,
+Expr * parseExprFromString(EvalState & state,
     const string & s, const Path & basePath)
 {
     return parse(state, s.c_str(), "(string)", basePath);
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 7dddc91a8..9d36fb6a0 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -4,8 +4,7 @@
 #include "store-api.hh"
 #include "util.hh"
 #include "archive.hh"
-#include "expr-to-xml.hh"
-#include "nixexpr-ast.hh"
+#include "value-to-xml.hh"
 #include "parser.hh"
 #include "names.hh"
 
@@ -14,87 +13,23 @@
 #include <unistd.h>
 
 #include <algorithm>
+#include <cstring>
 
 
 namespace nix {
 
 
 /*************************************************************
- * Constants
- *************************************************************/
-
-
-static Expr prim_builtins(EvalState & state, const ATermVector & args)
-{
-    /* Return an attribute set containing all primops.  This allows
-       Nix expressions to test for new primops and take appropriate
-       action if they're not available.  For instance, rather than
-       calling a primop `foo' directly, they could say `if builtins ?
-       foo then builtins.foo ... else ...'. */
-
-    ATermMap builtins(state.primOps.size());
-
-    for (ATermMap::const_iterator i = state.primOps.begin();
-         i != state.primOps.end(); ++i)
-    {
-        string name = aterm2String(i->key);
-        if (string(name, 0, 2) == "__")
-            name = string(name, 2);
-        /* !!! should use makePrimOp here, I guess. */
-        builtins.set(toATerm(name), makeAttrRHS(makeVar(i->key), makeNoPos()));
-    }
-
-    return makeAttrs(builtins);
-}
-
-
-/* Boolean constructors. */
-static Expr prim_true(EvalState & state, const ATermVector & args)
-{
-    return eTrue;
-}
-
-
-static Expr prim_false(EvalState & state, const ATermVector & args)
-{
-    return eFalse;
-}
-
-
-/* Return the null value. */
-static Expr prim_null(EvalState & state, const ATermVector & args)
-{
-    return makeNull();
-}
-
-
-/* Return a string constant representing the current platform.  Note!
-   that differs between platforms, so Nix expressions using
-   `__currentSystem' can evaluate to different values on different
-   platforms. */
-static Expr prim_currentSystem(EvalState & state, const ATermVector & args)
-{
-    return makeStr(thisSystem);
-}
-
-
-static Expr prim_currentTime(EvalState & state, const ATermVector & args)
-{
-    return ATmake("Int(<int>)", time(0));
-}
-
-
-/*************************************************************
  * Miscellaneous
  *************************************************************/
 
 
 /* Load and evaluate an expression from path specified by the
    argument. */ 
-static Expr prim_import(EvalState & state, const ATermVector & args)
+static void prim_import(EvalState & state, Value * * args, Value & v)
 {
     PathSet context;
-    Path path = coerceToPath(state, args[0], context);
+    Path path = state.coerceToPath(*args[0], context);
 
     for (PathSet::iterator i = context.begin(); i != context.end(); ++i) {
         assert(isStorePath(*i));
@@ -105,164 +40,203 @@ static Expr prim_import(EvalState & state, const ATermVector & args)
             store->buildDerivations(singleton<PathSet>(*i));
     }
 
-    return evalFile(state, path);
+    state.evalFile(path, v);
 }
 
 
 /* Determine whether the argument is the null value. */
-static Expr prim_isNull(EvalState & state, const ATermVector & args)
+static void prim_isNull(EvalState & state, Value * * args, Value & v)
 {
-    return makeBool(matchNull(evalExpr(state, args[0])));
+    state.forceValue(*args[0]);
+    mkBool(v, args[0]->type == tNull);
 }
 
 
 /* Determine whether the argument is a function. */
-static Expr prim_isFunction(EvalState & state, const ATermVector & args)
+static void prim_isFunction(EvalState & state, Value * * args, Value & v)
 {
-    Expr e = evalExpr(state, args[0]);
-    Pattern pat;
-    ATerm body, pos;
-    return makeBool(matchFunction(e, pat, body, pos));
+    state.forceValue(*args[0]);
+    mkBool(v, args[0]->type == tLambda);
 }
 
+
 /* Determine whether the argument is an Int. */
-static Expr prim_isInt(EvalState & state, const ATermVector & args)
+static void prim_isInt(EvalState & state, Value * * args, Value & v)
 {
-    int i;
-    return makeBool(matchInt(evalExpr(state, args[0]), i));
+    state.forceValue(*args[0]);
+    mkBool(v, args[0]->type == tInt);
 }
 
+
 /* Determine whether the argument is an String. */
-static Expr prim_isString(EvalState & state, const ATermVector & args)
+static void prim_isString(EvalState & state, Value * * args, Value & v)
 {
-    string s;
-    PathSet l;
-    return makeBool(matchStr(evalExpr(state, args[0]), s, l));
+    state.forceValue(*args[0]);
+    mkBool(v, args[0]->type == tString);
 }
 
+
 /* Determine whether the argument is an Bool. */
-static Expr prim_isBool(EvalState & state, const ATermVector & args)
+static void prim_isBool(EvalState & state, Value * * args, Value & v)
 {
-    ATermBool b;
-    return makeBool(matchBool(evalExpr(state, args[0]), b));
+    state.forceValue(*args[0]);
+    mkBool(v, args[0]->type == tBool);
 }
 
-static Expr prim_genericClosure(EvalState & state, const ATermVector & args)
+
+struct CompareValues
+{
+    bool operator () (const Value & v1, const Value & v2) const
+    {
+        if (v1.type != v2.type)
+            throw EvalError("cannot compare values of different types");
+        switch (v1.type) {
+            case tInt:
+                return v1.integer < v2.integer;
+            case tString:
+                return strcmp(v1.string.s, v2.string.s) < 0;
+            case tPath:
+                return strcmp(v1.path, v2.path) < 0;
+            default:
+                throw EvalError(format("cannot compare %1% with %2%") % showType(v1) % showType(v2));
+        }
+    }
+};
+
+
+static void prim_genericClosure(EvalState & state, Value * * args, Value & v)
 {
     startNest(nest, lvlDebug, "finding dependencies");
 
-    Expr attrs = evalExpr(state, args[0]);
+    state.forceAttrs(*args[0]);
 
     /* Get the start set. */
-    Expr startSet = queryAttr(attrs, "startSet");
-    if (!startSet) throw EvalError("attribute `startSet' required");
-    ATermList startSet2 = evalList(state, startSet);
+    Bindings::iterator startSet =
+        args[0]->attrs->find(state.symbols.create("startSet"));
+    if (startSet == args[0]->attrs->end())
+        throw EvalError("attribute `startSet' required");
+    state.forceList(startSet->second.value);
 
-    set<Expr> workSet; // !!! gc roots
-    for (ATermIterator i(startSet2); i; ++i) workSet.insert(*i);
+    list<Value *> workSet;
+    for (unsigned int n = 0; n < startSet->second.value.list.length; ++n)
+        workSet.push_back(startSet->second.value.list.elems[n]);
 
     /* Get the operator. */
-    Expr op = queryAttr(attrs, "operator");
-    if (!op) throw EvalError("attribute `operator' required");
-    
+    Bindings::iterator op =
+        args[0]->attrs->find(state.symbols.create("operator"));
+    if (op == args[0]->attrs->end())
+        throw EvalError("attribute `operator' required");
+    state.forceValue(op->second.value);
+
     /* Construct the closure by applying the operator to element of
        `workSet', adding the result to `workSet', continuing until
        no new elements are found. */
-    ATermList res = ATempty;
-    set<Expr> doneKeys; // !!! gc roots
+    list<Value> res;
+    set<Value, CompareValues> doneKeys;
     while (!workSet.empty()) {
-	Expr e = *(workSet.begin());
-	workSet.erase(e);
+	Value * e = *(workSet.begin());
+	workSet.pop_front();
 
-        e = strictEvalExpr(state, e);
+        state.forceAttrs(*e);
 
-        Expr key = queryAttr(e, "key");
-        if (!key) throw EvalError("attribute `key' required");
+        Bindings::iterator key =
+            e->attrs->find(state.symbols.create("key"));
+        if (key == e->attrs->end())
+            throw EvalError("attribute `key' required");
+        state.forceValue(key->second.value);
 
-	if (doneKeys.find(key) != doneKeys.end()) continue;
-        doneKeys.insert(key);
-        res = ATinsert(res, e);
+        if (doneKeys.find(key->second.value) != doneKeys.end()) continue;
+        doneKeys.insert(key->second.value);
+        res.push_back(*e);
         
         /* Call the `operator' function with `e' as argument. */
-        ATermList res = evalList(state, makeCall(op, e));
-
-        /* Try to find the dependencies relative to the `path'. */
-        for (ATermIterator i(res); i; ++i)
-            workSet.insert(evalExpr(state, *i));
+        Value call;
+        mkApp(call, op->second.value, *e);
+        state.forceList(call);
+
+        /* Add the values returned by the operator to the work set. */
+        for (unsigned int n = 0; n < call.list.length; ++n) {
+            state.forceValue(*call.list.elems[n]);
+            workSet.push_back(call.list.elems[n]);
+        }
     }
 
-    return makeList(res);
+    /* Create the result list. */
+    state.mkList(v, res.size());
+    Value * vs = state.allocValues(res.size());
+
+    unsigned int n = 0;
+    foreach (list<Value>::iterator, i, res) {
+        v.list.elems[n] = &vs[n];
+        vs[n++] = *i;
+    }
 }
 
 
-static Expr prim_abort(EvalState & state, const ATermVector & args)
+static void prim_abort(EvalState & state, Value * * args, Value & v)
 {
     PathSet context;
     throw Abort(format("evaluation aborted with the following error message: `%1%'") %
-        evalString(state, args[0], context));
+        state.coerceToString(*args[0], context));
 }
 
 
-static Expr prim_throw(EvalState & state, const ATermVector & args)
+static void prim_throw(EvalState & state, Value * * args, Value & v)
 {
     PathSet context;
     throw ThrownError(format("user-thrown exception: %1%") %
-        evalString(state, args[0], context));
+        state.coerceToString(*args[0], context));
 }
 
 
-static Expr prim_addErrorContext(EvalState & state, const ATermVector & args)
+static void prim_addErrorContext(EvalState & state, Value * * args, Value & v)
 {
-    PathSet context;
     try {
-        return evalExpr(state, args[1]);
+        state.forceValue(*args[1]);
+        v = *args[1];
     } catch (Error & e) {
-        e.addPrefix(format("%1%\n") %
-            evalString(state, args[0], context));
+        PathSet context;
+        e.addPrefix(format("%1%\n") % state.coerceToString(*args[0], context));
         throw;
     }
 }
 
+
 /* Try evaluating the argument. Success => {success=true; value=something;}, 
  * else => {success=false; value=false;} */
-static Expr prim_tryEval(EvalState & state, const ATermVector & args)
+static void prim_tryEval(EvalState & state, Value * * args, Value & v)
 {
-    ATermMap res = ATermMap();
+    state.mkAttrs(v);
     try {
-        Expr val = evalExpr(state, args[0]);
-        res.set(toATerm("value"), makeAttrRHS(val, makeNoPos()));
-        res.set(toATerm("success"), makeAttrRHS(eTrue, makeNoPos()));
+        state.forceValue(*args[0]);
+        (*v.attrs)[state.symbols.create("value")].value = *args[0];
+        mkBool((*v.attrs)[state.symbols.create("success")].value, true);
     } catch (AssertionError & e) {
-        printMsg(lvlDebug, format("tryEval caught an error: %1%: %2%") % e.prefix() % e.msg());
-        res.set(toATerm("value"), makeAttrRHS(eFalse, makeNoPos()));
-        res.set(toATerm("success"), makeAttrRHS(eFalse, makeNoPos()));
+        mkBool((*v.attrs)[state.symbols.create("value")].value, false);
+        mkBool((*v.attrs)[state.symbols.create("success")].value, false);
     }
-    return makeAttrs(res);
 }
 
 
 /* Return an environment variable.  Use with care. */
-static Expr prim_getEnv(EvalState & state, const ATermVector & args)
+static void prim_getEnv(EvalState & state, Value * * args, Value & v)
 {
-    string name = evalStringNoCtx(state, args[0]);
-    return makeStr(getEnv(name));
+    string name = state.forceStringNoCtx(*args[0]);
+    mkString(v, getEnv(name));
 }
 
 
-/* Evaluate the first expression, and print its abstract syntax tree
-   on standard error.  Then return the second expression.  Useful for
-   debugging.
- */
-static Expr prim_trace(EvalState & state, const ATermVector & args)
+/* Evaluate the first expression and print it on standard error.  Then
+   return the second expression.  Useful for debugging. */
+static void prim_trace(EvalState & state, Value * * args, Value & v)
 {
-    Expr e = evalExpr(state, args[0]);
-    string s;
-    PathSet context;
-    if (matchStr(e, s, context))
-        printMsg(lvlError, format("trace: %1%") % s);
+    state.forceValue(*args[0]);
+    if (args[0]->type == tString)
+        printMsg(lvlError, format("trace: %1%") % args[0]->string.s);
     else
-        printMsg(lvlError, format("trace: %1%") % e);
-    return evalExpr(state, args[1]);
+        printMsg(lvlError, format("trace: %1%") % *args[0]);
+    state.forceValue(*args[1]);
+    v = *args[1];
 }
 
 
@@ -324,7 +298,7 @@ static Hash hashDerivationModulo(EvalState & state, Derivation drv)
     }
     drv.inputDrvs = inputs2;
     
-    return hashTerm(unparseDerivation(drv));
+    return hashString(htSHA256, unparseDerivation(drv));
 }
 
 
@@ -335,28 +309,25 @@ static Hash hashDerivationModulo(EvalState & state, Derivation drv)
    derivation; `drvPath' containing the path of the Nix expression;
    and `type' set to `derivation' to indicate that this is a
    derivation. */
-static Expr prim_derivationStrict(EvalState & state, const ATermVector & args)
+static void prim_derivationStrict(EvalState & state, Value * * args, Value & v)
 {
     startNest(nest, lvlVomit, "evaluating derivation");
 
-    ATermMap attrs;
-    queryAllAttrs(evalExpr(state, args[0]), attrs, true);
+    state.forceAttrs(*args[0]);
 
-    /* Figure out the name already (for stack backtraces). */
-    ATerm posDrvName;
-    Expr eDrvName = attrs.get(toATerm("name"));
-    if (!eDrvName)
+    /* Figure out the name first (for stack backtraces). */
+    Bindings::iterator attr = args[0]->attrs->find(state.sName);
+    if (attr == args[0]->attrs->end())
         throw EvalError("required attribute `name' missing");
-    if (!matchAttrRHS(eDrvName, eDrvName, posDrvName)) abort();
     string drvName;
+    Pos & posDrvName(*attr->second.pos);
     try {        
-        drvName = evalStringNoCtx(state, eDrvName);
+        drvName = state.forceStringNoCtx(attr->second.value);
     } catch (Error & e) {
-        e.addPrefix(format("while evaluating the derivation attribute `name' at %1%:\n")
-            % showPos(posDrvName));
+        e.addPrefix(format("while evaluating the derivation attribute `name' at %1%:\n") % posDrvName);
         throw;
     }
-
+    
     /* Build the derivation expression by processing the attributes. */
     Derivation drv;
     
@@ -365,12 +336,8 @@ static Expr prim_derivationStrict(EvalState & state, const ATermVector & args)
     string outputHash, outputHashAlgo;
     bool outputHashRecursive = false;
 
-    for (ATermMap::const_iterator i = attrs.begin(); i != attrs.end(); ++i) {
-        string key = aterm2String(i->key);
-        ATerm value;
-        Expr pos;
-        ATerm rhs = i->value;
-        if (!matchAttrRHS(rhs, value, pos)) abort();
+    foreach (Bindings::iterator, i, *args[0]->attrs) {
+        string key = i->first;
         startNest(nest, lvlVomit, format("processing attribute `%1%'") % key);
 
         try {
@@ -378,15 +345,9 @@ static Expr prim_derivationStrict(EvalState & state, const ATermVector & args)
             /* The `args' attribute is special: it supplies the
                command-line arguments to the builder. */
             if (key == "args") {
-                ATermList es;
-                value = evalExpr(state, value);
-                if (!matchList(value, es)) {
-                    static bool haveWarned = false;
-                    warnOnce(haveWarned, "the `args' attribute should evaluate to a list");
-                    es = flattenList(state, value);
-                }
-                for (ATermIterator i(es); i; ++i) {
-                    string s = coerceToString(state, *i, context, true);
+                state.forceList(i->second.value);
+                for (unsigned int n = 0; n < i->second.value.list.length; ++n) {
+                    string s = state.coerceToString(*i->second.value.list.elems[n], context, true);
                     drv.args.push_back(s);
                 }
             }
@@ -394,11 +355,11 @@ static Expr prim_derivationStrict(EvalState & state, const ATermVector & args)
             /* All other attributes are passed to the builder through
                the environment. */
             else {
-                string s = coerceToString(state, value, context, true);
+                string s = state.coerceToString(i->second.value, context, true);
                 drv.env[key] = s;
                 if (key == "builder") drv.builder = s;
-                else if (key == "system") drv.platform = s;
-                else if (key == "name") drvName = s;
+                else if (i->first == state.sSystem) drv.platform = s;
+                else if (i->first == state.sName) drvName = s;
                 else if (key == "outputHash") outputHash = s;
                 else if (key == "outputHashAlgo") outputHashAlgo = s;
                 else if (key == "outputHashMode") {
@@ -410,12 +371,11 @@ static Expr prim_derivationStrict(EvalState & state, const ATermVector & args)
 
         } catch (Error & e) {
             e.addPrefix(format("while evaluating the derivation attribute `%1%' at %2%:\n")
-                % key % showPos(pos));
+                % key % *i->second.pos);
             e.addPrefix(format("while instantiating the derivation named `%1%' at %2%:\n")
-                % drvName % showPos(posDrvName));
+                % drvName % posDrvName);
             throw;
         }
-
     }
     
     /* Everything in the context of the strings in the derivation
@@ -523,33 +483,9 @@ static Expr prim_derivationStrict(EvalState & state, const ATermVector & args)
     state.drvHashes[drvPath] = hashDerivationModulo(state, drv);
 
     /* !!! assumes a single output */
-    ATermMap outAttrs(2);
-    outAttrs.set(toATerm("outPath"),
-        makeAttrRHS(makeStr(outPath, singleton<PathSet>(drvPath)), makeNoPos()));
-    outAttrs.set(toATerm("drvPath"),
-        makeAttrRHS(makeStr(drvPath, singleton<PathSet>("=" + drvPath)), makeNoPos()));
-
-    return makeAttrs(outAttrs);
-}
-
-
-static Expr prim_derivationLazy(EvalState & state, const ATermVector & args)
-{
-    Expr eAttrs = evalExpr(state, args[0]);
-    ATermMap attrs;    
-    queryAllAttrs(eAttrs, attrs, true);
-
-    attrs.set(toATerm("type"),
-        makeAttrRHS(makeStr("derivation"), makeNoPos()));
-
-    Expr drvStrict = makeCall(makeVar(toATerm("derivation!")), eAttrs);
-
-    attrs.set(toATerm("outPath"),
-        makeAttrRHS(makeSelect(drvStrict, toATerm("outPath")), makeNoPos()));
-    attrs.set(toATerm("drvPath"),
-        makeAttrRHS(makeSelect(drvStrict, toATerm("drvPath")), makeNoPos()));
-    
-    return makeAttrs(attrs);
+    state.mkAttrs(v);
+    mkString((*v.attrs)[state.sOutPath].value, outPath, singleton<PathSet>(drvPath));
+    mkString((*v.attrs)[state.sDrvPath].value, drvPath, singleton<PathSet>("=" + drvPath));
 }
 
 
@@ -559,11 +495,11 @@ static Expr prim_derivationLazy(EvalState & state, const ATermVector & args)
 
 
 /* Convert the argument to a path.  !!! obsolete? */
-static Expr prim_toPath(EvalState & state, const ATermVector & args)
+static void prim_toPath(EvalState & state, Value * * args, Value & v)
 {
     PathSet context;
-    string path = coerceToPath(state, args[0], context);
-    return makeStr(canonPath(path), context);
+    Path path = state.coerceToPath(*args[0], context);
+    mkString(v, canonPath(path), context);
 }
 
 
@@ -575,60 +511,58 @@ static Expr prim_toPath(EvalState & state, const ATermVector & args)
    /nix/store/newhash-oldhash-oldname.  In the past, `toPath' had
    special case behaviour for store paths, but that created weird
    corner cases. */
-static Expr prim_storePath(EvalState & state, const ATermVector & args)
+static void prim_storePath(EvalState & state, Value * * args, Value & v)
 {
     PathSet context;
-    Path path = canonPath(coerceToPath(state, args[0], context));
+    Path path = canonPath(state.coerceToPath(*args[0], context));
     if (!isInStore(path))
         throw EvalError(format("path `%1%' is not in the Nix store") % path);
     Path path2 = toStorePath(path);
     if (!store->isValidPath(path2))
         throw EvalError(format("store path `%1%' is not valid") % path2);
     context.insert(path2);
-    return makeStr(path, context);
+    mkString(v, path, context);
 }
 
 
-static Expr prim_pathExists(EvalState & state, const ATermVector & args)
+static void prim_pathExists(EvalState & state, Value * * args, Value & v)
 {
     PathSet context;
-    Path path = coerceToPath(state, args[0], context);
+    Path path = state.coerceToPath(*args[0], context);
     if (!context.empty())
         throw EvalError(format("string `%1%' cannot refer to other paths") % path);
-    return makeBool(pathExists(path));
+    mkBool(v, pathExists(path));
 }
 
 
 /* Return the base name of the given string, i.e., everything
    following the last slash. */
-static Expr prim_baseNameOf(EvalState & state, const ATermVector & args)
+static void prim_baseNameOf(EvalState & state, Value * * args, Value & v)
 {
     PathSet context;
-    return makeStr(baseNameOf(coerceToString(state, args[0], context)), context);
+    mkString(v, baseNameOf(state.coerceToString(*args[0], context)), context);
 }
 
 
 /* Return the directory of the given path, i.e., everything before the
    last slash.  Return either a path or a string depending on the type
    of the argument. */
-static Expr prim_dirOf(EvalState & state, const ATermVector & args)
+static void prim_dirOf(EvalState & state, Value * * args, Value & v)
 {
     PathSet context;
-    Expr e = evalExpr(state, args[0]); ATerm dummy;
-    bool isPath = matchPath(e, dummy);
-    Path dir = dirOf(coerceToPath(state, e, context));
-    return isPath ? makePath(toATerm(dir)) : makeStr(dir, context);
+    Path dir = dirOf(state.coerceToPath(*args[0], context));
+    if (args[0]->type == tPath) mkPath(v, dir.c_str()); else mkString(v, dir, context);
 }
 
 
 /* Return the contents of a file as a string. */
-static Expr prim_readFile(EvalState & state, const ATermVector & args)
+static void prim_readFile(EvalState & state, Value * * args, Value & v)
 {
     PathSet context;
-    Path path = coerceToPath(state, args[0], context);
+    Path path = state.coerceToPath(*args[0], context);
     if (!context.empty())
         throw EvalError(format("string `%1%' cannot refer to other paths") % path);
-    return makeStr(readFile(path));
+    mkString(v, readFile(path).c_str());
 }
 
 
@@ -640,26 +574,26 @@ static Expr prim_readFile(EvalState & state, const ATermVector & args)
 /* Convert the argument (which can be any Nix expression) to an XML
    representation returned in a string.  Not all Nix expressions can
    be sensibly or completely represented (e.g., functions). */
-static Expr prim_toXML(EvalState & state, const ATermVector & args)
+static void prim_toXML(EvalState & state, Value * * args, Value & v)
 {
     std::ostringstream out;
     PathSet context;
-    printTermAsXML(strictEvalExpr(state, args[0]), out, context);
-    return makeStr(out.str(), context);
+    printValueAsXML(state, true, false, *args[0], out, context);
+    mkString(v, out.str(), context);
 }
 
 
 /* Store a string in the Nix store as a source file that can be used
    as an input by derivations. */
-static Expr prim_toFile(EvalState & state, const ATermVector & args)
+static void prim_toFile(EvalState & state, Value * * args, Value & v)
 {
     PathSet context;
-    string name = evalStringNoCtx(state, args[0]);
-    string contents = evalString(state, args[1], context);
+    string name = state.forceStringNoCtx(*args[0]);
+    string contents = state.forceString(*args[1], context);
 
     PathSet refs;
 
-    for (PathSet::iterator i = context.begin(); i != context.end(); ++i) {
+    foreach (PathSet::iterator, i, context) {
         Path path = *i;
         if (path.at(0) == '=') path = string(path, 1);
         if (isDerivation(path))
@@ -674,17 +608,17 @@ static Expr prim_toFile(EvalState & state, const ATermVector & args)
     /* Note: we don't need to add `context' to the context of the
        result, since `storePath' itself has references to the paths
        used in args[1]. */
-    
-    return makeStr(storePath, singleton<PathSet>(storePath));
+
+    mkString(v, storePath, singleton<PathSet>(storePath));
 }
 
 
 struct FilterFromExpr : PathFilter
 {
     EvalState & state;
-    Expr filter;
+    Value & filter;
     
-    FilterFromExpr(EvalState & state, Expr filter)
+    FilterFromExpr(EvalState & state, Value & filter)
         : state(state), filter(filter)
     {
     }
@@ -695,35 +629,47 @@ struct FilterFromExpr : PathFilter
         if (lstat(path.c_str(), &st))
             throw SysError(format("getting attributes of path `%1%'") % path);
 
-        Expr call =
-            makeCall(
-                makeCall(filter, makeStr(path)),
-                makeStr(
-                    S_ISREG(st.st_mode) ? "regular" :
-                    S_ISDIR(st.st_mode) ? "directory" :
-                    S_ISLNK(st.st_mode) ? "symlink" :
-                    "unknown" /* not supported, will fail! */
-                    ));
-                
-        return evalBool(state, call);
+        /* Call the filter function.  The first argument is the path,
+           the second is a string indicating the type of the file. */
+        Value arg1;
+        mkString(arg1, path);
+
+        Value fun2;
+        state.callFunction(filter, arg1, fun2);
+
+        Value arg2;
+        mkString(arg2, 
+            S_ISREG(st.st_mode) ? "regular" :
+            S_ISDIR(st.st_mode) ? "directory" :
+            S_ISLNK(st.st_mode) ? "symlink" :
+            "unknown" /* not supported, will fail! */);
+        
+        Value res;
+        state.callFunction(fun2, arg2, res);
+
+        return state.forceBool(res);
     }
 };
 
 
-static Expr prim_filterSource(EvalState & state, const ATermVector & args)
+static void prim_filterSource(EvalState & state, Value * * args, Value & v)
 {
     PathSet context;
-    Path path = coerceToPath(state, args[1], context);
+    Path path = state.coerceToPath(*args[1], context);
     if (!context.empty())
         throw EvalError(format("string `%1%' cannot refer to other paths") % path);
 
-    FilterFromExpr filter(state, args[0]);
+    state.forceValue(*args[0]);
+    if (args[0]->type != tLambda)
+        throw TypeError(format("first argument in call to `filterSource' is not a function but %1%") % showType(*args[0]));
+
+    FilterFromExpr filter(state, *args[0]);
 
     Path dstPath = readOnlyMode
         ? computeStorePathForPath(path, true, htSHA256, filter).first
         : store->addToStore(path, true, htSHA256, filter);
 
-    return makeStr(dstPath, singleton<PathSet>(dstPath));
+    mkString(v, dstPath, singleton<PathSet>(dstPath));
 }
 
 
@@ -734,131 +680,119 @@ static Expr prim_filterSource(EvalState & state, const ATermVector & args)
 
 /* Return the names of the attributes in an attribute set as a sorted
    list of strings. */
-static Expr prim_attrNames(EvalState & state, const ATermVector & args)
+static void prim_attrNames(EvalState & state, Value * * args, Value & v)
 {
-    ATermMap attrs;
-    queryAllAttrs(evalExpr(state, args[0]), attrs);
+    state.forceAttrs(*args[0]);
 
-    StringSet names;
-    for (ATermMap::const_iterator i = attrs.begin(); i != attrs.end(); ++i)
-        names.insert(aterm2String(i->key));
+    state.mkList(v, args[0]->attrs->size());
+    Value * vs = state.allocValues(v.list.length);
 
-    ATermList list = ATempty;
-    for (StringSet::const_reverse_iterator i = names.rbegin();
-         i != names.rend(); ++i)
-        list = ATinsert(list, makeStr(*i, PathSet()));
+    StringSet names;
+    foreach (Bindings::iterator, i, *args[0]->attrs)
+        names.insert(i->first);
 
-    return makeList(list);
+    unsigned int n = 0;
+    foreach (StringSet::iterator, i, names) {
+        v.list.elems[n] = &vs[n];
+        mkString(vs[n++], *i);
+    }
 }
 
 
 /* Dynamic version of the `.' operator. */
-static Expr prim_getAttr(EvalState & state, const ATermVector & args)
+static void prim_getAttr(EvalState & state, Value * * args, Value & v)
 {
-    string attr = evalStringNoCtx(state, args[0]);
-    return evalExpr(state, makeSelect(args[1], toATerm(attr)));
+    string attr = state.forceStringNoCtx(*args[0]);
+    state.forceAttrs(*args[1]);
+    // !!! Should we create a symbol here or just do a lookup?
+    Bindings::iterator i = args[1]->attrs->find(state.symbols.create(attr));
+    if (i == args[1]->attrs->end())
+        throw EvalError(format("attribute `%1%' missing") % attr);
+    // !!! add to stack trace?
+    state.forceValue(i->second.value);
+    v = i->second.value;
 }
 
 
 /* Dynamic version of the `?' operator. */
-static Expr prim_hasAttr(EvalState & state, const ATermVector & args)
+static void prim_hasAttr(EvalState & state, Value * * args, Value & v)
 {
-    string attr = evalStringNoCtx(state, args[0]);
-    return evalExpr(state, makeOpHasAttr(args[1], toATerm(attr)));
+    string attr = state.forceStringNoCtx(*args[0]);
+    state.forceAttrs(*args[1]);
+    mkBool(v, args[1]->attrs->find(state.symbols.create(attr)) != args[1]->attrs->end());
 }
 
 
-/* Builds an attribute set from a list specifying (name, value)
-   pairs.  To be precise, a list [{name = "name1"; value = value1;}
-   ... {name = "nameN"; value = valueN;}] is transformed to {name1 =
-   value1; ... nameN = valueN;}. */
-static Expr prim_listToAttrs(EvalState & state, const ATermVector & args)
+/* Determine whether the argument is an attribute set. */
+static void prim_isAttrs(EvalState & state, Value * * args, Value & v)
 {
-    try {
-        ATermMap res = ATermMap();
-        ATermList list;
-        list = evalList(state, args[0]);
-        for (ATermIterator i(list); i; ++i){
-            // *i should now contain a pointer to the list item expression
-            ATermList attrs;
-            Expr evaledExpr = evalExpr(state, *i);
-            if (matchAttrs(evaledExpr, attrs)){
-                Expr e = evalExpr(state, makeSelect(evaledExpr, toATerm("name")));
-                string attr = evalStringNoCtx(state,e);
-                Expr r = makeSelect(evaledExpr, toATerm("value"));
-                res.set(toATerm(attr), makeAttrRHS(r, makeNoPos()));
-            }
-            else
-                throw TypeError(format("list element in `listToAttrs' is %s, expected a set { name = \"<name>\"; value = <value>; }")
-                    % showType(evaledExpr));
-        }
-    
-        return makeAttrs(res);
-    
-    } catch (Error & e) {
-        e.addPrefix(format("in `listToAttrs':\n"));
-        throw;
-    }
+    state.forceValue(*args[0]);
+    mkBool(v, args[0]->type == tAttrs);
 }
 
 
-static Expr prim_removeAttrs(EvalState & state, const ATermVector & args)
+static void prim_removeAttrs(EvalState & state, Value * * args, Value & v)
 {
-    ATermMap attrs;
-    queryAllAttrs(evalExpr(state, args[0]), attrs, true);
-    
-    ATermList list = evalList(state, args[1]);
+    state.forceAttrs(*args[0]);
+    state.forceList(*args[1]);
 
-    for (ATermIterator i(list); i; ++i)
-        /* It's not an error for *i not to exist. */
-        attrs.remove(toATerm(evalStringNoCtx(state, *i)));
+    state.cloneAttrs(*args[0], v);
 
-    return makeAttrs(attrs);
+    for (unsigned int i = 0; i < args[1]->list.length; ++i) {
+        state.forceStringNoCtx(*args[1]->list.elems[i]);
+        v.attrs->erase(state.symbols.create(args[1]->list.elems[i]->string.s));
+    }
 }
 
 
-/* Determine whether the argument is an attribute set. */
-static Expr prim_isAttrs(EvalState & state, const ATermVector & args)
+/* Builds an attribute set from a list specifying (name, value)
+   pairs.  To be precise, a list [{name = "name1"; value = value1;}
+   ... {name = "nameN"; value = valueN;}] is transformed to {name1 =
+   value1; ... nameN = valueN;}. */
+static void prim_listToAttrs(EvalState & state, Value * * args, Value & v)
 {
-    ATermList list;
-    return makeBool(matchAttrs(evalExpr(state, args[0]), list));
-}
+    state.forceList(*args[0]);
 
+    state.mkAttrs(v);
 
-/* Return the right-biased intersection of two attribute sets as1 and
-   as2, i.e. a set that contains every attribute from as2 that is also
-   a member of as1. */
-static Expr prim_intersectAttrs(EvalState & state, const ATermVector & args)
-{
-    ATermMap as1, as2;
-    queryAllAttrs(evalExpr(state, args[0]), as1, true);
-    queryAllAttrs(evalExpr(state, args[1]), as2, true);
-
-    ATermMap res;
-    foreach (ATermMap::const_iterator, i, as2)
-        if (as1[i->key]) res.set(i->key, i->value);
+    for (unsigned int i = 0; i < args[0]->list.length; ++i) {
+        Value & v2(*args[0]->list.elems[i]);
+        state.forceAttrs(v2);
+        
+        Bindings::iterator j = v2.attrs->find(state.sName);
+        if (j == v2.attrs->end())
+            throw TypeError("`name' attribute missing in a call to `listToAttrs'");
+        string name = state.forceStringNoCtx(j->second.value);
+        
+        j = v2.attrs->find(state.symbols.create("value"));
+        if (j == v2.attrs->end())
+            throw TypeError("`value' attribute missing in a call to `listToAttrs'");
 
-    return makeAttrs(res);
+        Attr & a = (*v.attrs)[state.symbols.create(name)];
+        mkCopy(a.value, j->second.value);
+        a.pos = j->second.pos;
+    }
 }
 
 
-static void attrsInPattern(ATermMap & map, Pattern pat)
+/* Return the right-biased intersection of two attribute sets as1 and
+   as2, i.e. a set that contains every attribute from as2 that is also
+   a member of as1. */
+static void prim_intersectAttrs(EvalState & state, Value * * args, Value & v)
 {
-    ATerm name;
-    ATermList formals;
-    Pattern pat1, pat2;
-    ATermBool ellipsis;
-    if (matchAttrsPat(pat, formals, ellipsis)) { 
-        for (ATermIterator i(formals); i; ++i) {
-            ATerm def;
-            if (!matchFormal(*i, name, def)) abort();
-            map.set(name, makeAttrRHS(makeBool(def != constNoDefaultValue), makeNoPos()));
+    state.forceAttrs(*args[0]);
+    state.forceAttrs(*args[1]);
+        
+    state.mkAttrs(v);
+    
+    foreach (Bindings::iterator, i, *args[1]->attrs) {
+        Bindings::iterator j = args[0]->attrs->find(i->first);
+        if (j != args[0]->attrs->end()) {
+            Attr & a = (*v.attrs)[i->first];
+            mkCopy(a.value, i->second.value);
+            a.pos = i->second.pos;
         }
     }
-    else if (matchAtPat(pat, pat1, pat2)) {
-        attrsInPattern(map, pat1);
-        attrsInPattern(map, pat2);
-    }
 }
 
 
@@ -875,17 +809,18 @@ static void attrsInPattern(ATermMap & map, Pattern pat)
       functionArgs (x: ...)
    => { }
 */
-static Expr prim_functionArgs(EvalState & state, const ATermVector & args)
+static void prim_functionArgs(EvalState & state, Value * * args, Value & v)
 {
-    Expr f = evalExpr(state, args[0]);
-    ATerm pat, body, pos;
-    if (!matchFunction(f, pat, body, pos))
-        throw TypeError("`functionArgs' required a function");
-    
-    ATermMap as;
-    attrsInPattern(as, pat);
+    state.forceValue(*args[0]);
+    if (args[0]->type != tLambda)
+        throw TypeError("`functionArgs' requires a function");
 
-    return makeAttrs(as);
+    state.mkAttrs(v);
+
+    if (!args[0]->lambda.fun->matchAttrs) return;
+
+    foreach (Formals::Formals_::iterator, i, args[0]->lambda.fun->formals->formals)
+        mkBool((*v.attrs)[i->name].value, i->def);
 }
 
 
@@ -895,53 +830,58 @@ static Expr prim_functionArgs(EvalState & state, const ATermVector & args)
 
 
 /* Determine whether the argument is a list. */
-static Expr prim_isList(EvalState & state, const ATermVector & args)
+static void prim_isList(EvalState & state, Value * * args, Value & v)
 {
-    ATermList list;
-    return makeBool(matchList(evalExpr(state, args[0]), list));
+    state.forceValue(*args[0]);
+    mkBool(v, args[0]->type == tList);
 }
 
 
 /* Return the first element of a list. */
-static Expr prim_head(EvalState & state, const ATermVector & args)
+static void prim_head(EvalState & state, Value * * args, Value & v)
 {
-    ATermList list = evalList(state, args[0]);
-    if (ATisEmpty(list))
+    state.forceList(*args[0]);
+    if (args[0]->list.length == 0)
         throw Error("`head' called on an empty list");
-    return evalExpr(state, ATgetFirst(list));
+    state.forceValue(*args[0]->list.elems[0]);
+    v = *args[0]->list.elems[0];
 }
 
 
 /* Return a list consisting of everything but the the first element of
    a list. */
-static Expr prim_tail(EvalState & state, const ATermVector & args)
+static void prim_tail(EvalState & state, Value * * args, Value & v)
 {
-    ATermList list = evalList(state, args[0]);
-    if (ATisEmpty(list))
+    state.forceList(*args[0]);
+    if (args[0]->list.length == 0)
         throw Error("`tail' called on an empty list");
-    return makeList(ATgetNext(list));
+    state.mkList(v, args[0]->list.length - 1);
+    for (unsigned int n = 0; n < v.list.length; ++n)
+        v.list.elems[n] = args[0]->list.elems[n + 1];
 }
 
 
 /* Apply a function to every element of a list. */
-static Expr prim_map(EvalState & state, const ATermVector & args)
+static void prim_map(EvalState & state, Value * * args, Value & v)
 {
-    Expr fun = evalExpr(state, args[0]);
-    ATermList list = evalList(state, args[1]);
+    state.forceFunction(*args[0]);
+    state.forceList(*args[1]);
 
-    ATermList res = ATempty;
-    for (ATermIterator i(list); i; ++i)
-        res = ATinsert(res, makeCall(fun, *i));
+    state.mkList(v, args[1]->list.length);
+    Value * vs = state.allocValues(v.list.length);
 
-    return makeList(ATreverse(res));
+    for (unsigned int n = 0; n < v.list.length; ++n) {
+        v.list.elems[n] = &vs[n];
+        mkApp(vs[n], *args[0], *args[1]->list.elems[n]);
+    }
 }
 
 
 /* Return the length of a list.  This is an O(1) time operation. */
-static Expr prim_length(EvalState & state, const ATermVector & args)
+static void prim_length(EvalState & state, Value * * args, Value & v)
 {
-    ATermList list = evalList(state, args[0]);
-    return makeInt(ATgetLength(list));
+    state.forceList(*args[0]);
+    mkInt(v, args[0]->list.length);
 }
 
 
@@ -950,44 +890,35 @@ static Expr prim_length(EvalState & state, const ATermVector & args)
  *************************************************************/
 
 
-static Expr prim_add(EvalState & state, const ATermVector & args)
+static void prim_add(EvalState & state, Value * * args, Value & v)
 {
-    int i1 = evalInt(state, args[0]);
-    int i2 = evalInt(state, args[1]);
-    return makeInt(i1 + i2);
+    mkInt(v, state.forceInt(*args[0]) + state.forceInt(*args[1]));
 }
 
 
-static Expr prim_sub(EvalState & state, const ATermVector & args)
+static void prim_sub(EvalState & state, Value * * args, Value & v)
 {
-    int i1 = evalInt(state, args[0]);
-    int i2 = evalInt(state, args[1]);
-    return makeInt(i1 - i2);
+    mkInt(v, state.forceInt(*args[0]) - state.forceInt(*args[1]));
 }
 
 
-static Expr prim_mul(EvalState & state, const ATermVector & args)
+static void prim_mul(EvalState & state, Value * * args, Value & v)
 {
-    int i1 = evalInt(state, args[0]);
-    int i2 = evalInt(state, args[1]);
-    return makeInt(i1 * i2);
+    mkInt(v, state.forceInt(*args[0]) * state.forceInt(*args[1]));
 }
 
 
-static Expr prim_div(EvalState & state, const ATermVector & args)
+static void prim_div(EvalState & state, Value * * args, Value & v)
 {
-    int i1 = evalInt(state, args[0]);
-    int i2 = evalInt(state, args[1]);
+    int i2 = state.forceInt(*args[1]);
     if (i2 == 0) throw EvalError("division by zero");
-    return makeInt(i1 / i2);
+    mkInt(v, state.forceInt(*args[0]) / i2);
 }
 
 
-static Expr prim_lessThan(EvalState & state, const ATermVector & args)
+static void prim_lessThan(EvalState & state, Value * * args, Value & v)
 {
-    int i1 = evalInt(state, args[0]);
-    int i2 = evalInt(state, args[1]);
-    return makeBool(i1 < i2);
+    mkBool(v, state.forceInt(*args[0]) < state.forceInt(*args[1]));
 }
 
 
@@ -999,11 +930,11 @@ static Expr prim_lessThan(EvalState & state, const ATermVector & args)
 /* Convert the argument to a string.  Paths are *not* copied to the
    store, so `toString /foo/bar' yields `"/foo/bar"', not
    `"/nix/store/whatever..."'. */
-static Expr prim_toString(EvalState & state, const ATermVector & args)
+static void prim_toString(EvalState & state, Value * * args, Value & v)
 {
     PathSet context;
-    string s = coerceToString(state, args[0], context, true, false);
-    return makeStr(s, context);
+    string s = state.coerceToString(*args[0], context, true, false);
+    mkString(v, s, context);
 }
 
 
@@ -1011,32 +942,32 @@ static Expr prim_toString(EvalState & state, const ATermVector & args)
    at character position `min(start, stringLength str)' inclusive and
    ending at `min(start + len, stringLength str)'.  `start' must be
    non-negative. */
-static Expr prim_substring(EvalState & state, const ATermVector & args)
+static void prim_substring(EvalState & state, Value * * args, Value & v)
 {
-    int start = evalInt(state, args[0]);
-    int len = evalInt(state, args[1]);
+    int start = state.forceInt(*args[0]);
+    int len = state.forceInt(*args[1]);
     PathSet context;
-    string s = coerceToString(state, args[2], context);
+    string s = state.coerceToString(*args[2], context);
 
     if (start < 0) throw EvalError("negative start position in `substring'");
 
-    return makeStr(string(s, start, len), context);
+    mkString(v, string(s, start, len), context);
 }
 
 
-static Expr prim_stringLength(EvalState & state, const ATermVector & args)
+static void prim_stringLength(EvalState & state, Value * * args, Value & v)
 {
     PathSet context;
-    string s = coerceToString(state, args[0], context);
-    return makeInt(s.size());
+    string s = state.coerceToString(*args[0], context);
+    mkInt(v, s.size());
 }
 
 
-static Expr prim_unsafeDiscardStringContext(EvalState & state, const ATermVector & args)
+static void prim_unsafeDiscardStringContext(EvalState & state, Value * * args, Value & v)
 {
     PathSet context;
-    string s = coerceToString(state, args[0], context);
-    return makeStr(s, PathSet());
+    string s = state.coerceToString(*args[0], context);
+    mkString(v, s, PathSet());
 }
 
 
@@ -1046,10 +977,10 @@ static Expr prim_unsafeDiscardStringContext(EvalState & state, const ATermVector
    source-only deployment).  This primop marks the string context so
    that builtins.derivation adds the path to drv.inputSrcs rather than
    drv.inputDrvs. */
-static Expr prim_unsafeDiscardOutputDependency(EvalState & state, const ATermVector & args)
+static void prim_unsafeDiscardOutputDependency(EvalState & state, Value * * args, Value & v)
 {
     PathSet context;
-    string s = coerceToString(state, args[0], context);
+    string s = state.coerceToString(*args[0], context);
 
     PathSet context2;
     foreach (PathSet::iterator, i, context) {
@@ -1058,29 +989,7 @@ static Expr prim_unsafeDiscardOutputDependency(EvalState & state, const ATermVec
         context2.insert(p);
     }
     
-    return makeStr(s, context2);
-}
-
-
-/* Expression serialization/deserialization */
-
-
-static Expr prim_exprToString(EvalState & state, const ATermVector & args)
-{
-    /* !!! this disregards context */
-    return makeStr(atPrint(evalExpr(state, args[0])));
-}
-
-
-static Expr prim_stringToExpr(EvalState & state, const ATermVector & args)
-{
-    /* !!! this can introduce arbitrary garbage terms in the
-       evaluator! */;
-    string s;
-    PathSet l;
-    if (!matchStr(evalExpr(state, args[0]), s, l))
-        throw EvalError("stringToExpr needs string argument!");
-    return ATreadFromString(s.c_str());
+    mkString(v, s, context2);
 }
 
 
@@ -1089,23 +998,21 @@ static Expr prim_stringToExpr(EvalState & state, const ATermVector & args)
  *************************************************************/
 
 
-static Expr prim_parseDrvName(EvalState & state, const ATermVector & args)
+static void prim_parseDrvName(EvalState & state, Value * * args, Value & v)
 {
-    string name = evalStringNoCtx(state, args[0]);
+    string name = state.forceStringNoCtx(*args[0]);
     DrvName parsed(name);
-    ATermMap attrs(2);
-    attrs.set(toATerm("name"), makeAttrRHS(makeStr(parsed.name), makeNoPos()));
-    attrs.set(toATerm("version"), makeAttrRHS(makeStr(parsed.version), makeNoPos()));
-    return makeAttrs(attrs);
+    state.mkAttrs(v);
+    mkString((*v.attrs)[state.sName].value, parsed.name);
+    mkString((*v.attrs)[state.symbols.create("version")].value, parsed.version);
 }
 
 
-static Expr prim_compareVersions(EvalState & state, const ATermVector & args)
+static void prim_compareVersions(EvalState & state, Value * * args, Value & v)
 {
-    string version1 = evalStringNoCtx(state, args[0]);
-    string version2 = evalStringNoCtx(state, args[1]);
-    int d = compareVersions(version1, version2);
-    return makeInt(d);
+    string version1 = state.forceStringNoCtx(*args[0]);
+    string version2 = state.forceStringNoCtx(*args[1]);
+    mkInt(v, compareVersions(version1, version2));
 }
 
 
@@ -1114,16 +1021,31 @@ static Expr prim_compareVersions(EvalState & state, const ATermVector & args)
  *************************************************************/
 
 
-void EvalState::addPrimOps()
+void EvalState::createBaseEnv()
 {
-    addPrimOp("builtins", 0, prim_builtins);
-        
-    // Constants
-    addPrimOp("true", 0, prim_true);
-    addPrimOp("false", 0, prim_false);
-    addPrimOp("null", 0, prim_null);
-    addPrimOp("__currentSystem", 0, prim_currentSystem);
-    addPrimOp("__currentTime", 0, prim_currentTime);
+    baseEnv.up = 0;
+
+    /* Add global constants such as `true' to the base environment. */
+    Value v;
+
+    /* `builtins' must be first! */
+    mkAttrs(v);
+    addConstant("builtins", v);
+
+    mkBool(v, true);
+    addConstant("true", v);
+    
+    mkBool(v, false);
+    addConstant("false", v);
+    
+    v.type = tNull;
+    addConstant("null", v);
+
+    mkInt(v, time(0));
+    addConstant("__currentTime", v);
+
+    mkString(v, thisSystem.c_str());
+    addConstant("__currentSystem", v);
 
     // Miscellaneous
     addPrimOp("import", 1, prim_import);
@@ -1140,14 +1062,14 @@ void EvalState::addPrimOps()
     addPrimOp("__getEnv", 1, prim_getEnv);
     addPrimOp("__trace", 2, prim_trace);
 
-    
-    // Expr <-> String
-    addPrimOp("__exprToString", 1, prim_exprToString);
-    addPrimOp("__stringToExpr", 1, prim_stringToExpr);
-
     // Derivations
-    addPrimOp("derivation!", 1, prim_derivationStrict);
-    addPrimOp("derivation", 1, prim_derivationLazy);
+    addPrimOp("derivationStrict", 1, prim_derivationStrict);
+
+    /* Add a wrapper around the derivation primop that computes the
+       `drvPath' and `outPath' attributes lazily. */
+    string s = "attrs: let res = derivationStrict attrs; in attrs // { drvPath = res.drvPath; outPath = res.outPath; type = \"derivation\"; }";
+    mkThunk(v, baseEnv, parseExprFromString(*this, s, "/"));
+    addConstant("derivation", v);
 
     // Paths
     addPrimOp("__toPath", 1, prim_toPath);
@@ -1178,7 +1100,7 @@ void EvalState::addPrimOps()
     addPrimOp("__tail", 1, prim_tail);
     addPrimOp("map", 2, prim_map);
     addPrimOp("__length", 1, prim_length);
-
+    
     // Integer arithmetic
     addPrimOp("__add", 2, prim_add);
     addPrimOp("__sub", 2, prim_sub);
@@ -1195,7 +1117,7 @@ void EvalState::addPrimOps()
 
     // Versions
     addPrimOp("__parseDrvName", 1, prim_parseDrvName);
-    addPrimOp("__compareVersions", 2, prim_compareVersions);
+    addPrimOp("__compareVersions", 2, prim_compareVersions);    
 }
 
 
diff --git a/src/libexpr/symbol-table.hh b/src/libexpr/symbol-table.hh
new file mode 100644
index 000000000..424c23538
--- /dev/null
+++ b/src/libexpr/symbol-table.hh
@@ -0,0 +1,81 @@
+#ifndef __SYMBOL_TABLE_H
+#define __SYMBOL_TABLE_H
+
+#include <map>
+#include <tr1/unordered_set>
+
+#include "types.hh"
+
+namespace nix {
+
+/* Symbol table used by the parser and evaluator to represent and look
+   up identifiers and attribute sets efficiently.
+   SymbolTable::create() converts a string into a symbol.  Symbols
+   have the property that they can be compared efficiently (using a
+   pointer equality test), because the symbol table stores only one
+   copy of each string. */
+
+class Symbol
+{
+private:
+    const string * s; // pointer into SymbolTable
+    Symbol(const string * s) : s(s) { };
+    friend class SymbolTable;
+
+public:
+    bool operator == (const Symbol & s2) const
+    {
+        return s == s2.s;
+    }
+    
+    bool operator != (const Symbol & s2) const
+    {
+        return s != s2.s;
+    }
+    
+    bool operator < (const Symbol & s2) const
+    {
+        return s < s2.s;
+    }
+
+    operator const string & () const
+    {
+        return *s;
+    }
+
+    bool empty() const
+    {
+        return s->empty();
+    }
+
+    friend std::ostream & operator << (std::ostream & str, const Symbol & sym);
+};
+
+inline std::ostream & operator << (std::ostream & str, const Symbol & sym)
+{
+    str << *sym.s;
+    return str;
+}
+
+class SymbolTable
+{
+private:
+    typedef std::tr1::unordered_set<string> Symbols;
+    Symbols symbols;
+
+public:
+    Symbol create(const string & s)
+    {
+        std::pair<Symbols::iterator, bool> res = symbols.insert(s);
+        return Symbol(&*res.first);
+    }
+
+    unsigned int size() const
+    {
+        return symbols.size();
+    }
+};
+
+}
+
+#endif /* !__SYMBOL_TABLE_H */
diff --git a/src/libexpr/value-to-xml.cc b/src/libexpr/value-to-xml.cc
new file mode 100644
index 000000000..e751fd300
--- /dev/null
+++ b/src/libexpr/value-to-xml.cc
@@ -0,0 +1,161 @@
+#include "value-to-xml.hh"
+#include "xml-writer.hh"
+#include "util.hh"
+
+#include <cstdlib>
+
+
+namespace nix {
+
+    
+static XMLAttrs singletonAttrs(const string & name, const string & value)
+{
+    XMLAttrs attrs;
+    attrs[name] = value;
+    return attrs;
+}
+
+
+static void printValueAsXML(EvalState & state, bool strict, bool location,
+    Value & v, XMLWriter & doc, PathSet & context, PathSet & drvsSeen);
+
+
+static void posToXML(XMLAttrs & xmlAttrs, const Pos & pos)
+{
+    xmlAttrs["path"] = pos.file;
+    xmlAttrs["line"] = (format("%1%") % pos.line).str();
+    xmlAttrs["column"] = (format("%1%") % pos.column).str();
+}
+
+
+static void showAttrs(EvalState & state, bool strict, bool location,
+    Bindings & attrs, XMLWriter & doc, PathSet & context, PathSet & drvsSeen)
+{
+    StringSet names;
+    
+    foreach (Bindings::iterator, i, attrs)
+        names.insert(i->first);
+    
+    foreach (StringSet::iterator, i, names) {
+        Attr & a(attrs[state.symbols.create(*i)]);
+        
+        XMLAttrs xmlAttrs;
+        xmlAttrs["name"] = *i;
+        if (location && a.pos != &noPos) posToXML(xmlAttrs, *a.pos);
+        
+        XMLOpenElement _(doc, "attr", xmlAttrs);
+        printValueAsXML(state, strict, location,
+            a.value, doc, context, drvsSeen);
+    }
+}
+
+
+static void printValueAsXML(EvalState & state, bool strict, bool location,
+    Value & v, XMLWriter & doc, PathSet & context, PathSet & drvsSeen)
+{
+    checkInterrupt();
+
+    if (strict) state.forceValue(v);
+        
+    switch (v.type) {
+
+        case tInt:
+            doc.writeEmptyElement("int", singletonAttrs("value", (format("%1%") % v.integer).str()));
+            break;
+
+        case tBool:
+            doc.writeEmptyElement("bool", singletonAttrs("value", v.boolean ? "true" : "false"));
+            break;
+
+        case tString:
+            /* !!! show the context? */
+            doc.writeEmptyElement("string", singletonAttrs("value", v.string.s));
+            break;
+
+        case tPath:
+            doc.writeEmptyElement("path", singletonAttrs("value", v.path));
+            break;
+
+        case tNull:
+            doc.writeEmptyElement("null");
+            break;
+
+        case tAttrs:
+            if (state.isDerivation(v)) {
+                XMLAttrs xmlAttrs;
+            
+                Bindings::iterator a = v.attrs->find(state.symbols.create("derivation"));
+
+                Path drvPath;
+                a = v.attrs->find(state.sDrvPath);
+                if (a != v.attrs->end()) {
+                    if (strict) state.forceValue(a->second.value);
+                    if (a->second.value.type == tString)
+                        xmlAttrs["drvPath"] = drvPath = a->second.value.string.s;
+                }
+        
+                a = v.attrs->find(state.sOutPath);
+                if (a != v.attrs->end()) {
+                    if (strict) state.forceValue(a->second.value);
+                    if (a->second.value.type == tString)
+                        xmlAttrs["outPath"] = a->second.value.string.s;
+                }
+
+                XMLOpenElement _(doc, "derivation", xmlAttrs);
+
+                if (drvPath != "" && drvsSeen.find(drvPath) == drvsSeen.end()) {
+                    drvsSeen.insert(drvPath);
+                    showAttrs(state, strict, location, *v.attrs, doc, context, drvsSeen);
+                } else
+                    doc.writeEmptyElement("repeated");
+            }
+
+            else {
+                XMLOpenElement _(doc, "attrs");
+                showAttrs(state, strict, location, *v.attrs, doc, context, drvsSeen);
+            }
+            
+            break;
+
+        case tList: {
+            XMLOpenElement _(doc, "list");
+            for (unsigned int n = 0; n < v.list.length; ++n)
+                printValueAsXML(state, strict, location, *v.list.elems[n], doc, context, drvsSeen);
+            break;
+        }
+
+        case tLambda: {
+            XMLAttrs xmlAttrs;
+            if (location) posToXML(xmlAttrs, v.lambda.fun->pos);
+            XMLOpenElement _(doc, "function", xmlAttrs);
+            
+            if (v.lambda.fun->matchAttrs) {
+                XMLAttrs attrs;
+                if (!v.lambda.fun->arg.empty()) attrs["name"] = v.lambda.fun->arg;
+                if (v.lambda.fun->formals->ellipsis) attrs["ellipsis"] = "1";
+                XMLOpenElement _(doc, "attrspat", attrs);
+                foreach (Formals::Formals_::iterator, i, v.lambda.fun->formals->formals)
+                    doc.writeEmptyElement("attr", singletonAttrs("name", i->name));
+            } else
+                doc.writeEmptyElement("varpat", singletonAttrs("name", v.lambda.fun->arg));
+            
+            break;
+        }
+
+        default:
+            doc.writeEmptyElement("unevaluated");
+    }
+}
+
+
+void printValueAsXML(EvalState & state, bool strict, bool location,
+    Value & v, std::ostream & out, PathSet & context)
+{
+    XMLWriter doc(true, out);
+    XMLOpenElement root(doc, "expr");
+    PathSet drvsSeen;    
+    printValueAsXML(state, strict, location, v, doc, context, drvsSeen);
+}
+
+ 
+}
diff --git a/src/libexpr/value-to-xml.hh b/src/libexpr/value-to-xml.hh
new file mode 100644
index 000000000..0c6de3a8b
--- /dev/null
+++ b/src/libexpr/value-to-xml.hh
@@ -0,0 +1,17 @@
+#ifndef __VALUE_TO_XML_H
+#define __VALUE_TO_XML_H
+
+#include <string>
+#include <map>
+
+#include "nixexpr.hh"
+#include "eval.hh"
+
+namespace nix {
+
+void printValueAsXML(EvalState & state, bool strict, bool location,
+    Value & v, std::ostream & out, PathSet & context);
+    
+}
+
+#endif /* !__VALUE_TO_XML_H */
diff --git a/src/libmain/Makefile.am b/src/libmain/Makefile.am
index c2946febc..a9ee66042 100644
--- a/src/libmain/Makefile.am
+++ b/src/libmain/Makefile.am
@@ -15,5 +15,5 @@ AM_CXXFLAGS = \
  -DNIX_LIBEXEC_DIR=\"$(libexecdir)\" \
  -DNIX_BIN_DIR=\"$(bindir)\" \
  -DNIX_VERSION=\"$(VERSION)\" \
- -I$(srcdir)/.. ${aterm_include} -I$(srcdir)/../libutil \
+ -I$(srcdir)/.. -I$(srcdir)/../libutil \
  -I$(srcdir)/../libstore
diff --git a/src/libmain/shared.cc b/src/libmain/shared.cc
index d9cf9a862..3fbec4b52 100644
--- a/src/libmain/shared.cc
+++ b/src/libmain/shared.cc
@@ -13,8 +13,6 @@
 #include <sys/stat.h>
 #include <unistd.h>
 
-#include <aterm2.h>
-
 
 namespace nix {
 
@@ -87,9 +85,6 @@ static void setLogType(string lt)
 }
 
 
-void initDerivationsHelpers();
-
-
 static void closeStore()
 {
     try {
@@ -176,9 +171,6 @@ static void initAndRun(int argc, char * * argv)
     string lt = getEnv("NIX_LOG_TYPE");
     if (lt != "") setLogType(lt);
 
-    /* ATerm stuff.  !!! find a better place to put this */
-    initDerivationsHelpers();
-    
     /* Put the arguments in a vector. */
     Strings args, remaining;
     while (argc--) args.push_back(*argv++);
@@ -333,10 +325,6 @@ int main(int argc, char * * argv)
     if (argc == 0) abort();
     setuidInit();
     
-    /* ATerm setup. */
-    ATerm bottomOfStack;
-    ATinit(argc, argv, &bottomOfStack);
-
     /* Turn on buffering for cerr. */
 #if HAVE_PUBSETBUF
     std::cerr.rdbuf()->pubsetbuf(buf, sizeof(buf));
diff --git a/src/libstore/Makefile.am b/src/libstore/Makefile.am
index 863871519..9accc3005 100644
--- a/src/libstore/Makefile.am
+++ b/src/libstore/Makefile.am
@@ -12,12 +12,5 @@ pkginclude_HEADERS = \
 
 libstore_la_LIBADD = ../libutil/libutil.la ../boost/format/libformat.la @ADDITIONAL_NETWORK_LIBS@
 
-BUILT_SOURCES = derivations-ast.cc derivations-ast.hh
-
-EXTRA_DIST = derivations-ast.def derivations-ast.cc
-
 AM_CXXFLAGS = -Wall \
- -I$(srcdir)/.. ${aterm_include} -I$(srcdir)/../libutil
-
-derivations-ast.cc derivations-ast.hh: ../aterm-helper.pl derivations-ast.def
-	$(perl) $(srcdir)/../aterm-helper.pl derivations-ast.hh derivations-ast.cc < $(srcdir)/derivations-ast.def
+ -I$(srcdir)/.. -I$(srcdir)/../libutil
diff --git a/src/libstore/derivations-ast.def b/src/libstore/derivations-ast.def
deleted file mode 100644
index 574529ae7..000000000
--- a/src/libstore/derivations-ast.def
+++ /dev/null
@@ -1,10 +0,0 @@
-init initDerivationsHelpers
-
-Derive | ATermList ATermList ATermList string string ATermList ATermList | ATerm |
-
-| string string | ATerm | EnvBinding |
-| string ATermList | ATerm | DerivationInput |
-| string string string string | ATerm | DerivationOutput |
-
-Closure | ATermList ATermList | ATerm | OldClosure |
-| string ATermList | ATerm | OldClosureElem |
diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
index bc2ec1f90..e321ae8aa 100644
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -1,22 +1,12 @@
 #include "derivations.hh"
 #include "store-api.hh"
-#include "aterm.hh"
 #include "globals.hh"
 #include "util.hh"
 
-#include "derivations-ast.hh"
-#include "derivations-ast.cc"
-
 
 namespace nix {
 
 
-Hash hashTerm(ATerm t)
-{
-    return hashString(htSHA256, atPrint(t));
-}
-
-
 Path writeDerivation(const Derivation & drv, const string & name)
 {
     PathSet references;
@@ -27,137 +17,151 @@ Path writeDerivation(const Derivation & drv, const string & name)
        (that can be missing (of course) and should not necessarily be
        held during a garbage collection). */
     string suffix = name + drvExtension;
-    string contents = atPrint(unparseDerivation(drv));
+    string contents = unparseDerivation(drv);
     return readOnlyMode
         ? computeStorePathForText(suffix, contents, references)
         : store->addTextToStore(suffix, contents, references);
 }
 
 
-static void checkPath(const string & s)
+static Path parsePath(std::istream & str)
 {
+    string s = parseString(str);
     if (s.size() == 0 || s[0] != '/')
         throw Error(format("bad path `%1%' in derivation") % s);
+    return s;
 }
     
 
-static void parseStrings(ATermList paths, StringSet & out, bool arePaths)
+static StringSet parseStrings(std::istream & str, bool arePaths)
 {
-    for (ATermIterator i(paths); i; ++i) {
-        if (ATgetType(*i) != AT_APPL)
-            throw badTerm("not a path", *i);
-        string s = aterm2String(*i);
-        if (arePaths) checkPath(s);
-        out.insert(s);
-    }
+    StringSet res;
+    while (!endOfList(str))
+        res.insert(arePaths ? parsePath(str) : parseString(str));
+    return res;
 }
+    
 
-
-/* Shut up warnings. */
-void throwBadDrv(ATerm t) __attribute__ ((noreturn));
-
-void throwBadDrv(ATerm t) 
-{
-    throw badTerm("not a valid derivation", t);
-}
-
-
-Derivation parseDerivation(ATerm t)
+Derivation parseDerivation(const string & s)
 {
     Derivation drv;
-    ATermList outs, inDrvs, inSrcs, args, bnds;
-    ATerm builder, platform;
+    std::istringstream str(s);
+    expect(str, "Derive([");
 
-    if (!matchDerive(t, outs, inDrvs, inSrcs, platform, builder, args, bnds))
-        throwBadDrv(t);
-
-    for (ATermIterator i(outs); i; ++i) {
-        ATerm id, path, hashAlgo, hash;
-        if (!matchDerivationOutput(*i, id, path, hashAlgo, hash))
-            throwBadDrv(t);
+    /* Parse the list of outputs. */
+    while (!endOfList(str)) {
         DerivationOutput out;
-        out.path = aterm2String(path);
-        checkPath(out.path);
-        out.hashAlgo = aterm2String(hashAlgo);
-        out.hash = aterm2String(hash);
-        drv.outputs[aterm2String(id)] = out;
+        expect(str, "("); string id = parseString(str);
+        expect(str, ","); out.path = parsePath(str);
+        expect(str, ","); out.hashAlgo = parseString(str);
+        expect(str, ","); out.hash = parseString(str);
+        expect(str, ")");
+        drv.outputs[id] = out;
     }
 
-    for (ATermIterator i(inDrvs); i; ++i) {
-        ATerm drvPath;
-        ATermList ids;
-        if (!matchDerivationInput(*i, drvPath, ids))
-            throwBadDrv(t);
-        Path drvPath2 = aterm2String(drvPath);
-        checkPath(drvPath2);
-        StringSet ids2;
-        parseStrings(ids, ids2, false);
-        drv.inputDrvs[drvPath2] = ids2;
+    /* Parse the list of input derivations. */
+    expect(str, ",[");
+    while (!endOfList(str)) {
+        expect(str, "(");
+        Path drvPath = parsePath(str);
+        expect(str, ",[");
+        drv.inputDrvs[drvPath] = parseStrings(str, false);
+        expect(str, ")");
     }
-    
-    parseStrings(inSrcs, drv.inputSrcs, true);
 
-    drv.builder = aterm2String(builder);
-    drv.platform = aterm2String(platform);
-    
-    for (ATermIterator i(args); i; ++i) {
-        if (ATgetType(*i) != AT_APPL)
-            throw badTerm("string expected", *i);
-        drv.args.push_back(aterm2String(*i));
+    expect(str, ",["); drv.inputSrcs = parseStrings(str, true);
+    expect(str, ","); drv.platform = parseString(str);
+    expect(str, ","); drv.builder = parseString(str);
+
+    /* Parse the builder arguments. */
+    expect(str, ",[");
+    while (!endOfList(str))
+        drv.args.push_back(parseString(str));
+
+    /* Parse the environment variables. */
+    expect(str, ",[");
+    while (!endOfList(str)) {
+        expect(str, "("); string name = parseString(str);
+        expect(str, ","); string value = parseString(str);
+        expect(str, ")");
+        drv.env[name] = value;
     }
+    
+    expect(str, ")");
+    return drv;
+}
 
-    for (ATermIterator i(bnds); i; ++i) {
-        ATerm s1, s2;
-        if (!matchEnvBinding(*i, s1, s2))
-            throw badTerm("tuple of strings expected", *i);
-        drv.env[aterm2String(s1)] = aterm2String(s2);
-    }
 
-    return drv;
+static void printString(string & res, const string & s)
+{
+    res += '"';
+    for (const char * i = s.c_str(); *i; i++)
+        if (*i == '\"' || *i == '\\') { res += "\\"; res += *i; }
+        else if (*i == '\n') res += "\\n";
+        else if (*i == '\r') res += "\\r";
+        else if (*i == '\t') res += "\\t";
+        else res += *i;
+    res += '"';
 }
 
 
-ATerm unparseDerivation(const Derivation & drv)
+template<class ForwardIterator>
+static void printStrings(string & res, ForwardIterator i, ForwardIterator j)
 {
-    ATermList outputs = ATempty;
-    for (DerivationOutputs::const_reverse_iterator i = drv.outputs.rbegin();
-         i != drv.outputs.rend(); ++i)
-        outputs = ATinsert(outputs,
-            makeDerivationOutput(
-                toATerm(i->first),
-                toATerm(i->second.path),
-                toATerm(i->second.hashAlgo),
-                toATerm(i->second.hash)));
-
-    ATermList inDrvs = ATempty;
-    for (DerivationInputs::const_reverse_iterator i = drv.inputDrvs.rbegin();
-         i != drv.inputDrvs.rend(); ++i)
-        inDrvs = ATinsert(inDrvs,
-            makeDerivationInput(
-                toATerm(i->first),
-                toATermList(i->second)));
+    res += '[';
+    bool first = true;
+    for ( ; i != j; ++i) {
+        if (first) first = false; else res += ',';
+        printString(res, *i);
+    }
+    res += ']';
+}
+
+
+string unparseDerivation(const Derivation & drv)
+{
+    string s;
+    s.reserve(65536);
+    s += "Derive([";
+
+    bool first = true;
+    foreach (DerivationOutputs::const_iterator, i, drv.outputs) {
+        if (first) first = false; else s += ',';
+        s += '('; printString(s, i->first);
+        s += ','; printString(s, i->second.path);
+        s += ','; printString(s, i->second.hashAlgo);
+        s += ','; printString(s, i->second.hash);
+        s += ')';
+    }
+
+    s += "],[";
+    first = true;
+    foreach (DerivationInputs::const_iterator, i, drv.inputDrvs) {
+        if (first) first = false; else s += ',';
+        s += '('; printString(s, i->first);
+        s += ','; printStrings(s, i->second.begin(), i->second.end());
+        s += ')';
+    }
+
+    s += "],";
+    printStrings(s, drv.inputSrcs.begin(), drv.inputSrcs.end());
+    
+    s += ','; printString(s, drv.platform);
+    s += ','; printString(s, drv.builder);
+    s += ','; printStrings(s, drv.args.begin(), drv.args.end());
+
+    s += ",[";
+    first = true;
+    foreach (StringPairs::const_iterator, i, drv.env) {
+        if (first) first = false; else s += ',';
+        s += '('; printString(s, i->first);
+        s += ','; printString(s, i->second);
+        s += ')';
+    }
+    
+    s += "])";
     
-    ATermList args = ATempty;
-    for (Strings::const_reverse_iterator i = drv.args.rbegin();
-         i != drv.args.rend(); ++i)
-        args = ATinsert(args, toATerm(*i));
-
-    ATermList env = ATempty;
-    for (StringPairs::const_reverse_iterator i = drv.env.rbegin();
-         i != drv.env.rend(); ++i)
-        env = ATinsert(env,
-            makeEnvBinding(
-                toATerm(i->first),
-                toATerm(i->second)));
-
-    return makeDerive(
-        outputs,
-        inDrvs,
-        toATermList(drv.inputSrcs),
-        toATerm(drv.platform),
-        toATerm(drv.builder),
-        args,
-        env);
+    return s;
 }
 
 
diff --git a/src/libstore/derivations.hh b/src/libstore/derivations.hh
index 042f4738d..95e49d42c 100644
--- a/src/libstore/derivations.hh
+++ b/src/libstore/derivations.hh
@@ -1,8 +1,6 @@
 #ifndef __DERIVATIONS_H
 #define __DERIVATIONS_H
 
-#include <aterm1.h>
-
 #include "hash.hh"
 
 #include <map>
@@ -53,17 +51,14 @@ struct Derivation
 };
 
 
-/* Hash an aterm. */
-Hash hashTerm(ATerm t);
-
 /* Write a derivation to the Nix store, and return its path. */
 Path writeDerivation(const Derivation & drv, const string & name);
 
 /* Parse a derivation. */
-Derivation parseDerivation(ATerm t);
+Derivation parseDerivation(const string & s);
 
-/* Parse a derivation. */
-ATerm unparseDerivation(const Derivation & drv);
+/* Print a derivation. */
+string unparseDerivation(const Derivation & drv);
 
 /* Check whether a file name ends with the extensions for
    derivations. */
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index a83ba55e2..2c0aa3579 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -3,8 +3,6 @@
 #include "globals.hh"
 #include "archive.hh"
 #include "pathlocks.hh"
-#include "aterm.hh"
-#include "derivations-ast.hh"
 #include "worker-protocol.hh"
     
 #include <iostream>
diff --git a/src/libstore/misc.cc b/src/libstore/misc.cc
index 2d7d13a0e..f2cc20626 100644
--- a/src/libstore/misc.cc
+++ b/src/libstore/misc.cc
@@ -2,8 +2,6 @@
 #include "store-api.hh"
 #include "local-store.hh"
 
-#include <aterm2.h>
-
 
 namespace nix {
 
@@ -12,9 +10,7 @@ Derivation derivationFromPath(const Path & drvPath)
 {
     assertStorePath(drvPath);
     store->ensurePath(drvPath);
-    ATerm t = ATreadFromNamedFile(drvPath.c_str());
-    if (!t) throw Error(format("cannot read aterm from `%1%'") % drvPath);
-    return parseDerivation(t);
+    return parseDerivation(readFile(drvPath));
 }
 
 
diff --git a/src/libutil/Makefile.am b/src/libutil/Makefile.am
index bd0996543..aa862208c 100644
--- a/src/libutil/Makefile.am
+++ b/src/libutil/Makefile.am
@@ -1,16 +1,16 @@
 pkglib_LTLIBRARIES = libutil.la
 
 libutil_la_SOURCES = util.cc hash.cc serialise.cc \
-  archive.cc aterm.cc aterm-map.cc xml-writer.cc
+  archive.cc xml-writer.cc
 
 libutil_la_LIBADD = ../boost/format/libformat.la
 
 pkginclude_HEADERS = util.hh hash.hh serialise.hh \
-  archive.hh aterm.hh aterm-map.hh xml-writer.hh types.hh
+  archive.hh xml-writer.hh types.hh
 
 if !HAVE_OPENSSL
 libutil_la_SOURCES += \
  md5.c md5.h sha1.c sha1.h sha256.c sha256.h md32_common.h
 endif
 
-AM_CXXFLAGS = -Wall -I$(srcdir)/.. ${aterm_include}
+AM_CXXFLAGS = -Wall -I$(srcdir)/..
diff --git a/src/libutil/aterm-map.cc b/src/libutil/aterm-map.cc
deleted file mode 100644
index c31fcdba3..000000000
--- a/src/libutil/aterm-map.cc
+++ /dev/null
@@ -1,332 +0,0 @@
-#include "aterm-map.hh"
-
-#include <iostream>
-
-#include <assert.h>
-#include <stdlib.h>
-
-#include <aterm2.h>
-
-
-namespace nix {
-
-
-static const unsigned int maxLoadFactor = /* 1 / */ 3;
-static unsigned int nrResizes = 0;
-static unsigned int sizeTotalAlloc = 0;
-static unsigned int sizeCurAlloc = 0;
-static unsigned int sizeMaxAlloc = 0;
-
-
-ATermMap::ATermMap(unsigned int expectedCount)
-{
-    init(expectedCount);
-}
-
-
-ATermMap::ATermMap(const ATermMap & map)
-{
-    init(map.maxCount);
-    copy(map.hashTable, map.capacity);
-}
-
-
-ATermMap & ATermMap::operator = (const ATermMap & map)
-{
-    if (this == &map) return *this;
-    free();
-    init(map.maxCount);
-    copy(map.hashTable, map.capacity);
-    return *this;
-}
-
-
-ATermMap::~ATermMap()
-{
-    free();
-}
-
-
-void ATermMap::init(unsigned int expectedCount)
-{
-    assert(sizeof(ATerm) * 2 == sizeof(KeyValue));
-    capacity = 0;
-    count = 0;
-    maxCount = 0;
-    hashTable = 0;
-    resizeTable(expectedCount);
-}
-
-
-void ATermMap::free()
-{
-    if (hashTable) {
-        ATunprotectArray((ATerm *) hashTable);
-        ::free(hashTable);
-        sizeCurAlloc -= sizeof(KeyValue) * capacity;
-        hashTable = 0;
-    }
-}
-
-
-static unsigned int roundToPowerOf2(unsigned int x)
-{
-    x--;
-    x |= x >> 1; x |= x >> 2; x |= x >> 4; x |= x >> 8; x |= x >> 16;
-    x++;
-    return x;
-}
-
-
-void ATermMap::resizeTable(unsigned int expectedCount)
-{
-    if (expectedCount == 0) expectedCount = 1;
-//     cout << maxCount << " -> " << expectedCount << endl;
-//     cout << maxCount << " " << size << endl;
-//     cout << (double) size / maxCount << endl;
-
-    unsigned int oldCapacity = capacity;
-    KeyValue * oldHashTable = hashTable;
-
-    maxCount = expectedCount;
-    capacity = roundToPowerOf2(maxCount * maxLoadFactor);
-    hashTable = (KeyValue *) calloc(sizeof(KeyValue), capacity);
-    sizeTotalAlloc += sizeof(KeyValue) * capacity;
-    sizeCurAlloc += sizeof(KeyValue) * capacity;
-    if (sizeCurAlloc > sizeMaxAlloc) sizeMaxAlloc = sizeCurAlloc;
-    ATprotectArray((ATerm *) hashTable, capacity * 2);
-    
-//     cout << capacity << endl;
-
-    /* Re-hash the elements in the old table. */
-    if (oldCapacity != 0) {
-        count = 0;
-        copy(oldHashTable, oldCapacity);
-        ATunprotectArray((ATerm *) oldHashTable);
-        ::free(oldHashTable);
-        sizeCurAlloc -= sizeof(KeyValue) * oldCapacity;
-        nrResizes++;
-    }
-}
-
-
-void ATermMap::copy(KeyValue * elements, unsigned int capacity)
-{
-    for (unsigned int i = 0; i < capacity; ++i)
-        if (elements[i].value) /* i.e., non-empty, non-deleted element */
-            set(elements[i].key, elements[i].value);
-}
-
-
-/* !!! use a bigger shift for 64-bit platforms? */
-static const unsigned int shift = 16;
-static const unsigned long knuth = (unsigned long) (0.6180339887 * (1 << shift));
-
-
-unsigned long ATermMap::hash1(ATerm key) const
-{
-    /* Don't care about the least significant bits of the ATerm
-       pointer since they're always 0. */
-    unsigned long key2 = ((unsigned long) key) >> 2;
-
-    /* Approximately equal to:
-    double d = key2 * 0.6180339887;
-    unsigned int h = (int) (capacity * (d - floor(d)));
-    */
- 
-    unsigned long h = (capacity * ((key2 * knuth) & ((1 << shift) - 1))) >> shift;
-
-    return h;
-}
-
-
-unsigned long ATermMap::hash2(ATerm key) const
-{
-    unsigned long key2 = ((unsigned long) key) >> 2;
-    /* Note: the result must be relatively prime to `capacity' (which
-       is a power of 2), so we make sure that the result is always
-       odd. */
-    unsigned long h = ((key2 * 134217689) & (capacity - 1)) | 1;
-    return h;
-}
-
-
-static unsigned int nrItemsSet = 0;
-static unsigned int nrSetProbes = 0;
-
-
-void ATermMap::set(ATerm key, ATerm value)
-{
-    if (count == maxCount) resizeTable(capacity * 2 / maxLoadFactor);
-    
-    nrItemsSet++;
-    for (unsigned int i = 0, h = hash1(key); i < capacity;
-         ++i, h = (h + hash2(key)) & (capacity - 1))
-    {
-        // assert(h < capacity);
-        nrSetProbes++;
-        /* Note: to see whether a slot is free, we check
-           hashTable[h].value, not hashTable[h].key, since we use
-           value == 0 to mark deleted slots. */
-        if (hashTable[h].value == 0 || hashTable[h].key == key) {
-            if (hashTable[h].value == 0) count++;
-            hashTable[h].key = key;
-            hashTable[h].value = value;
-            return;
-        }
-    }
-        
-    abort();
-}
-
-
-static unsigned int nrItemsGet = 0;
-static unsigned int nrGetProbes = 0;
-
-
-ATerm ATermMap::get(ATerm key) const
-{
-    nrItemsGet++;
-    for (unsigned int i = 0, h = hash1(key); i < capacity;
-         ++i, h = (h + hash2(key)) & (capacity - 1))
-    {
-        nrGetProbes++;
-        if (hashTable[h].key == 0) return 0;
-        if (hashTable[h].key == key) return hashTable[h].value;
-    }
-    return 0;
-}
-
-
-void ATermMap::remove(ATerm key)
-{
-    for (unsigned int i = 0, h = hash1(key); i < capacity;
-         ++i, h = (h + hash2(key)) & (capacity - 1))
-    {
-        if (hashTable[h].key == 0) return;
-        if (hashTable[h].key == key) {
-            if (hashTable[h].value != 0) {
-                hashTable[h].value = 0;
-                count--;
-            }
-            return;
-        }
-    }
-}
-
-
-unsigned int ATermMap::size()
-{
-    return count; /* STL nomenclature */
-}
-
-
-void printATermMapStats()
-{
-    using std::cerr;
-    using std::endl;
-    
-    cerr << "RESIZES: " << nrResizes << " "
-         << sizeTotalAlloc << " "
-         << sizeCurAlloc << " "
-         << sizeMaxAlloc << endl;
-        
-    cerr << "SET: "
-         << nrItemsSet << " "
-         << nrSetProbes << " "
-         << (double) nrSetProbes / nrItemsSet << endl;
-
-    cerr << "GET: "
-         << nrItemsGet << " "
-         << nrGetProbes << " "
-         << (double) nrGetProbes / nrItemsGet << endl;
-}
-
-
-#if 0
-int main(int argc, char * * argv)
-{
-    ATerm bottomOfStack;
-    ATinit(argc, argv, &bottomOfStack);
-
-    /* Make test terms. */
-    int nrTestTerms = 100000;
-    ATerm testTerms[nrTestTerms];
-
-    for (int i = 0; i < nrTestTerms; ++i) {
-        char name[10];
-        sprintf(name, "%d", (int) random() % 37);
-
-        int arity = i == 0 ? 0 : (random() % 37);
-        ATerm kids[arity];
-        for (int j = 0; j < arity; ++j)
-            kids[j] = testTerms[random() % i];
-        
-        testTerms[i] = (ATerm) ATmakeApplArray(ATmakeAFun(name, arity, ATfalse), kids);
-//         ATwriteToSharedTextFile(testTerms[i], stdout);
-//         printf("\n");
-    }
-
-
-    cout << "testing...\n";
-
-    
-    #define someTerm() (testTerms[(int) random() % nrTestTerms])
-
-
-    for (int test = 0; test < 100000; ++test) {
-        //cerr << test << endl;
-        unsigned int n = 300;
-        ATermMap map(300);
-        ATerm keys[n], values[n];
-        for (unsigned int i = 0; i < n; ++i) {
-            keys[i] = someTerm();
-            values[i] = someTerm();
-            map.set(keys[i], values[i]);
-            //cerr << "INSERT: " << keys[i] << " " << values[i] << endl;
-        }
-
-        unsigned int size = map.size();
-        assert(size <= n);
-        values[n - 1] = 0;
-        map.remove(keys[n - 1]);
-        assert(map.size() == size - 1);
-
-        unsigned int checksum;
-        unsigned int count = 0;
-        for (ATermMap::const_iterator i = map.begin(); i != map.end(); ++i, ++count) {
-            assert(i->key);
-            assert(i->value);
-            checksum += (unsigned int) (*i).key;
-            checksum += (unsigned int) (*i).value;
-            // cout << (*i).key << " " << (*i).value << endl;
-        }
-        assert(count == size - 1);
-
-        for (unsigned int i = 0; i < n; ++i) {
-            for (unsigned int j = i + 1; j < n; ++j)
-                if (keys[i] == keys[j]) goto x;
-            if (map.get(keys[i]) != values[i]) {
-                cerr << "MISMATCH: " << keys[i] << " " << values[i] << " " << map.get(keys[i]) << " " << i << endl;
-                abort();
-            }
-            if (values[i] != 0) {
-                checksum -= (unsigned int) keys[i];
-                checksum -= (unsigned int) values[i];
-            }
-        x:  ;
-        }
-
-        assert(checksum == 0);
-        
-        for (unsigned int i = 0; i < 100; ++i)
-            map.get(someTerm());
-        
-    }
-
-    printATermMapStats();
-}
-#endif
-
- 
-}
diff --git a/src/libutil/aterm-map.hh b/src/libutil/aterm-map.hh
deleted file mode 100644
index b732453a7..000000000
--- a/src/libutil/aterm-map.hh
+++ /dev/null
@@ -1,129 +0,0 @@
-#ifndef __ATERM_MAP_H
-#define __ATERM_MAP_H
-
-#include <aterm1.h>
-#include <assert.h>
-
-
-namespace nix {
-
-
-class ATermMap
-{
-public:
-
-    struct KeyValue
-    {
-        ATerm key;
-        ATerm value;
-    };
-
-private:
-
-    /* Hash table for the map.  We use open addressing, i.e., all
-       key/value pairs are stored directly in the table, and there are
-       no pointers.  Collisions are resolved through probing. */
-    KeyValue * hashTable;
-
-    /* Current size of the hash table. */
-    unsigned int capacity;
-
-    /* Number of elements in the hash table. */
-    unsigned int count;
-
-    /* Maximum number of elements in the hash table.  If `count'
-       exceeds this number, the hash table is expanded. */
-    unsigned int maxCount;
-    
-public:
-
-    /* Create a map.  `expectedCount' is the number of elements the
-       map is expected to hold. */
-    ATermMap(unsigned int expectedCount = 16);
-    
-    ATermMap(const ATermMap & map);
-    
-    ~ATermMap();
-
-    ATermMap & operator = (const ATermMap & map);
-        
-    void set(ATerm key, ATerm value);
-
-    ATerm get(ATerm key) const;
-
-    ATerm operator [](ATerm key) const
-    {
-        return get(key);
-    }
-
-    void remove(ATerm key);
-
-    unsigned int size();
-
-    struct const_iterator
-    {
-        const ATermMap & map;
-        unsigned int pos;
-        const_iterator(const ATermMap & map, int pos) : map(map)
-        {
-            this->pos = pos;
-        }
-        bool operator !=(const const_iterator & i)
-        {
-            return pos != i.pos;
-        }
-        void operator ++()
-        {
-            if (pos == map.capacity) return;
-            do { ++pos; 
-            } while (pos < map.capacity && map.hashTable[pos].value == 0);
-        }
-        const KeyValue & operator *()
-        {
-            assert(pos < map.capacity);
-            return map.hashTable[pos];
-        }
-        const KeyValue * operator ->()
-        {
-            assert(pos < map.capacity);
-            return &map.hashTable[pos];
-        }
-    };
-
-    friend class ATermMap::const_iterator;
-    
-    const_iterator begin() const
-    {
-        unsigned int i = 0;
-        while (i < capacity && hashTable[i].value == 0) ++i;
-        return const_iterator(*this, i);
-    }
-    
-    const_iterator end() const
-    {
-        return const_iterator(*this, capacity);
-    }
-
-private:
-    
-    void init(unsigned int expectedCount);
-
-    void free();
-
-    void resizeTable(unsigned int expectedCount);
-
-    void copy(KeyValue * elements, unsigned int capacity);
-    
-    inline unsigned long hash1(ATerm key) const;
-    inline unsigned long hash2(ATerm key) const;
-};
-
-
-/* Hack. */
-void printATermMapStats();
-
- 
-}
-
-
-#endif /* !__ATERM_MAP_H */
diff --git a/src/libutil/aterm.cc b/src/libutil/aterm.cc
deleted file mode 100644
index 25d704785..000000000
--- a/src/libutil/aterm.cc
+++ /dev/null
@@ -1,55 +0,0 @@
-#include "aterm.hh"
-
-#include <cstring>
-
-using std::string;
-
-
-string nix::atPrint(ATerm t)
-{
-    if (!t) throw Error("attempt to print null aterm");
-    char * s = ATwriteToString(t);
-    if (!s) throw Error("cannot print term");
-    return s;
-}
-
-
-std::ostream & operator << (std::ostream & stream, ATerm e)
-{
-    return stream << nix::atPrint(e);
-}
-
-
-nix::Error nix::badTerm(const format & f, ATerm t)
-{
-    char * s = ATwriteToString(t);
-    if (!s) throw Error("cannot print term");
-    if (strlen(s) > 1000) {
-        int len;
-        s = ATwriteToSharedString(t, &len);
-        if (!s) throw Error("cannot print term");
-    }
-    return Error(format("%1%, in `%2%'") % f.str() % (string) s);
-}
-
-
-ATerm nix::toATerm(const char * s)
-{
-    return (ATerm) ATmakeAppl0(ATmakeAFun((char *) s, 0, ATtrue));
-}
-
-
-ATerm nix::toATerm(const string & s)
-{
-    return toATerm(s.c_str());
-}
-
-
-ATermList nix::toATermList(const StringSet & ss)
-{
-    ATermList l = ATempty;
-    for (StringSet::const_reverse_iterator i = ss.rbegin();
-         i != ss.rend(); ++i)
-        l = ATinsert(l, toATerm(*i));
-    return l;
-}
diff --git a/src/libutil/aterm.hh b/src/libutil/aterm.hh
deleted file mode 100644
index b1cbc3b6d..000000000
--- a/src/libutil/aterm.hh
+++ /dev/null
@@ -1,55 +0,0 @@
-#ifndef __ATERM_H
-#define __ATERM_H
-
-#include <aterm2.h>
-
-#include "types.hh"
-
-
-namespace nix {
-
-
-/* Print an ATerm. */
-string atPrint(ATerm t);
-
-class ATermIterator
-{
-    ATermList t;
-
-public:
-    ATermIterator(ATermList _t) : t(_t) { }
-    ATermIterator & operator ++ ()
-    {
-        t = ATgetNext(t);
-        return *this;
-    }
-    ATerm operator * ()
-    {
-        return ATgetFirst(t);
-    }
-    operator bool ()
-    {
-        return t != ATempty;
-    }
-};
-
-
-/* Throw an exception with an error message containing the given
-   aterm. */
-Error badTerm(const format & f, ATerm t);
-
-
-/* Convert strings to ATerms. */
-ATerm toATerm(const char * s);
-ATerm toATerm(const string & s);
-
-ATermList toATermList(const StringSet & ss);
- 
-}
-
-
-/* Write an ATerm to an output stream. */
-std::ostream & operator << (std::ostream & stream, ATerm e);
-
-
-#endif /* !__ATERM_H */
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 790c25768..98912e7a0 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -951,53 +951,6 @@ void _interrupted()
 //////////////////////////////////////////////////////////////////////
 
 
-string packStrings(const Strings & strings)
-{
-    string d;
-    for (Strings::const_iterator i = strings.begin();
-         i != strings.end(); ++i)
-    {
-        unsigned int len = i->size();
-        d += len & 0xff;
-        d += (len >> 8) & 0xff;
-        d += (len >> 16) & 0xff;
-        d += (len >> 24) & 0xff;
-        d += *i;
-    }
-    return d;
-}
-
-    
-Strings unpackStrings(const string & s)
-{
-    Strings strings;
-    
-    string::const_iterator i = s.begin();
-    
-    while (i != s.end()) {
-
-        if (i + 4 > s.end())
-            throw Error(format("short db entry: `%1%'") % s);
-        
-        unsigned int len;
-        len = (unsigned char) *i++;
-        len |= ((unsigned char) *i++) << 8;
-        len |= ((unsigned char) *i++) << 16;
-        len |= ((unsigned char) *i++) << 24;
-
-        if (len == 0xffffffff) return strings; /* explicit end-of-list */
-        
-        if (i + len > s.end())
-            throw Error(format("short db entry: `%1%'") % s);
-
-        strings.push_back(string(i, i + len));
-        i += len;
-    }
-    
-    return strings;
-}
-
-
 Strings tokenizeString(const string & s, const string & separators)
 {
     Strings result;
@@ -1053,6 +1006,47 @@ bool hasSuffix(const string & s, const string & suffix)
 }
 
 
+void expect(std::istream & str, const string & s)
+{
+    char s2[s.size()];
+    str.read(s2, s.size());
+    if (string(s2, s.size()) != s)
+        throw Error(format("expected string `%1%'") % s);
+}
+
+
+string parseString(std::istream & str)
+{
+    string res;
+    expect(str, "\"");
+    int c;
+    while ((c = str.get()) != '"')
+        if (c == '\\') {
+            c = str.get();
+            if (c == 'n') res += '\n';
+            else if (c == 'r') res += '\r';
+            else if (c == 't') res += '\t';
+            else res += c;
+        }
+        else res += c;
+    return res;
+}
+
+
+bool endOfList(std::istream & str)
+{
+    if (str.peek() == ',') {
+        str.get();
+        return false;
+    }
+    if (str.peek() == ']') {
+        str.get();
+        return true;
+    }
+    return false;
+}
+
+
 void ignoreException()
 {
     try {
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index f609e8944..ff710077c 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -15,7 +15,7 @@ namespace nix {
 
 
 #define foreach(it_type, it, collection)                                \
-    for (it_type it = collection.begin(); it != collection.end(); ++it)
+    for (it_type it = (collection).begin(); it != (collection).end(); ++it)
 
 
 /* Return an environment variable. */
@@ -276,11 +276,6 @@ void inline checkInterrupt()
 MakeError(Interrupted, BaseError)
 
 
-/* String packing / unpacking. */
-string packStrings(const Strings & strings);
-Strings unpackStrings(const string & s);
-
-
 /* String tokenizer. */
 Strings tokenizeString(const string & s, const string & separators = " \t\n\r");
 
@@ -307,32 +302,21 @@ string int2String(int n);
 bool hasSuffix(const string & s, const string & suffix);
 
 
-/* Exception handling in destructors: print an error message, then
-   ignore the exception. */
-void ignoreException();
+/* Read string `s' from stream `str'. */
+void expect(std::istream & str, const string & s);
 
 
-/* STL functions such as sort() pass a binary function object around
-   by value, so it gets cloned a lot.  This is bad if the function
-   object has state or is simply large.  This adapter wraps the
-   function object to simulate passing by reference. */
-template<class F>
-struct binary_function_ref_adapter
-{
-    F * p;
+/* Read a C-style string from stream `str'. */
+string parseString(std::istream & str);
 
-    binary_function_ref_adapter(F * _p)
-    {
-        p = _p;
-    }
-    
-    typename F::result_type operator () (
-        const typename F::first_argument_type & x,
-        const typename F::second_argument_type & y)
-    {
-        return (*p)(x, y);
-    }
-};
+
+/* Utility function used to parse legacy ATerms. */
+bool endOfList(std::istream & str);
+
+
+/* Exception handling in destructors: print an error message, then
+   ignore the exception. */
+void ignoreException();
 
 
 }
diff --git a/src/nix-env/Makefile.am b/src/nix-env/Makefile.am
index 900524f76..7dfa7425a 100644
--- a/src/nix-env/Makefile.am
+++ b/src/nix-env/Makefile.am
@@ -1,9 +1,10 @@
 bin_PROGRAMS = nix-env
 
-nix_env_SOURCES = nix-env.cc profiles.cc profiles.hh help.txt
+nix_env_SOURCES = nix-env.cc profiles.cc profiles.hh user-env.cc user-env.hh help.txt
+
 nix_env_LDADD = ../libmain/libmain.la ../libexpr/libexpr.la \
  ../libstore/libstore.la ../libutil/libutil.la \
- ../boost/format/libformat.la ${aterm_lib} @ADDITIONAL_NETWORK_LIBS@
+ ../boost/format/libformat.la @ADDITIONAL_NETWORK_LIBS@
 
 nix-env.o: help.txt.hh
 
@@ -11,6 +12,6 @@ nix-env.o: help.txt.hh
 	../bin2c/bin2c helpText < $< > $@ || (rm $@ && exit 1)
 
 AM_CXXFLAGS = \
- -I$(srcdir)/.. ${aterm_include} \
+ -I$(srcdir)/.. \
  -I$(srcdir)/../libutil -I$(srcdir)/../libstore \
  -I$(srcdir)/../libexpr -I$(srcdir)/../libmain -I../libexpr
diff --git a/src/nix-env/nix-env.cc b/src/nix-env/nix-env.cc
index 35caf687b..12a256a09 100644
--- a/src/nix-env/nix-env.cc
+++ b/src/nix-env/nix-env.cc
@@ -6,13 +6,12 @@
 #include "parser.hh"
 #include "eval.hh"
 #include "help.txt.hh"
-#include "nixexpr-ast.hh"
 #include "get-drvs.hh"
 #include "attr-path.hh"
-#include "pathlocks.hh"
 #include "common-opts.hh"
 #include "xml-writer.hh"
 #include "store-api.hh"
+#include "user-env.hh"
 #include "util.hh"
 
 #include <cerrno>
@@ -47,7 +46,7 @@ struct InstallSourceInfo
     Path profile; /* for srcProfile */
     string systemFilter; /* for srcNixExprDrvs */
     bool prebuiltOnly;
-    ATermMap autoArgs;
+    Bindings autoArgs;
     InstallSourceInfo() : prebuiltOnly(false) { };
 };
 
@@ -112,7 +111,7 @@ static bool isNixExpr(const Path & path)
 
 
 static void getAllExprs(EvalState & state,
-    const Path & path, ATermMap & attrs)
+    const Path & path, ExprAttrs & attrs)
 {
     Strings names = readDirectory(path);
     StringSet namesSorted(names.begin(), names.end());
@@ -132,8 +131,8 @@ static void getAllExprs(EvalState & state,
             string attrName = *i;
             if (hasSuffix(attrName, ".nix"))
                 attrName = string(attrName, 0, attrName.size() - 4);
-            attrs.set(toATerm(attrName), makeAttrRHS(
-                    parseExprFromFile(state, absPath(path2)), makeNoPos()));
+            attrs.attrs[state.symbols.create(attrName)] =
+                ExprAttrs::Attr(parseExprFromFile(state, absPath(path2)), noPos);
         }
         else
             /* `path2' is a directory (with no default.nix in it);
@@ -143,7 +142,7 @@ static void getAllExprs(EvalState & state,
 }
 
 
-static Expr loadSourceExpr(EvalState & state, const Path & path)
+static Expr * loadSourceExpr(EvalState & state, const Path & path)
 {
     if (isNixExpr(path)) return parseExprFromFile(state, absPath(path));
 
@@ -153,20 +152,22 @@ static Expr loadSourceExpr(EvalState & state, const Path & path)
        (but keep the attribute set flat, not nested, to make it easier
        for a user to have a ~/.nix-defexpr directory that includes
        some system-wide directory). */
-    ATermMap attrs;
-    attrs.set(toATerm("_combineChannels"), makeAttrRHS(makeList(ATempty), makeNoPos()));
-    getAllExprs(state, path, attrs);
-    return makeAttrs(attrs);
+    ExprAttrs * attrs = new ExprAttrs;
+    attrs->attrs[state.symbols.create("_combineChannels")] =
+        ExprAttrs::Attr(new ExprList(), noPos);
+    getAllExprs(state, path, *attrs);
+    return attrs;
 }
 
 
 static void loadDerivations(EvalState & state, Path nixExprPath,
-    string systemFilter, const ATermMap & autoArgs,
+    string systemFilter, const Bindings & autoArgs,
     const string & pathPrefix, DrvInfos & elems)
 {
-    getDerivations(state,
-        findAlongAttrPath(state, pathPrefix, autoArgs, loadSourceExpr(state, nixExprPath)),
-        pathPrefix, autoArgs, elems);
+    Value v;
+    findAlongAttrPath(state, pathPrefix, autoArgs, loadSourceExpr(state, nixExprPath), v);
+    
+    getDerivations(state, v, pathPrefix, autoArgs, elems);
 
     /* Filter out all derivations not applicable to the current
        system. */
@@ -192,172 +193,6 @@ static Path getDefNixExprPath()
 }
 
 
-struct AddPos : TermFun
-{
-    ATerm operator () (ATerm e)
-    {
-        ATerm x, y;
-        if (matchObsoleteBind(e, x, y))
-            return makeBind(x, y, makeNoPos());
-        if (matchObsoleteStr(e, x))
-            return makeStr(x, ATempty);
-        return e;
-    }
-};
-
-
-static DrvInfos queryInstalled(EvalState & state, const Path & userEnv)
-{
-    Path path = userEnv + "/manifest";
-
-    if (!pathExists(path))
-        return DrvInfos(); /* not an error, assume nothing installed */
-
-    Expr e = ATreadFromNamedFile(path.c_str());
-    if (!e) throw Error(format("cannot read Nix expression from `%1%'") % path);
-
-    /* Compatibility: Bind(x, y) -> Bind(x, y, NoPos). */
-    AddPos addPos;
-    e = bottomupRewrite(addPos, e);
-
-    DrvInfos elems;
-    getDerivations(state, e, "", ATermMap(1), elems);
-    return elems;
-}
-
-
-/* Ensure exclusive access to a profile.  Any command that modifies
-   the profile first acquires this lock. */
-static void lockProfile(PathLocks & lock, const Path & profile)
-{
-    lock.lockPaths(singleton<PathSet>(profile),
-        (format("waiting for lock on profile `%1%'") % profile).str());
-    lock.setDeletion(true);
-}
-
-
-/* Optimistic locking is used by long-running operations like `nix-env
-   -i'.  Instead of acquiring the exclusive lock for the entire
-   duration of the operation, we just perform the operation
-   optimistically (without an exclusive lock), and check at the end
-   whether the profile changed while we were busy (i.e., the symlink
-   target changed).  If so, the operation is restarted.  Restarting is
-   generally cheap, since the build results are still in the Nix
-   store.  Most of the time, only the user environment has to be
-   rebuilt. */
-static string optimisticLockProfile(const Path & profile)
-{
-    return pathExists(profile) ? readLink(profile) : "";
-}
-
-
-static bool createUserEnv(EvalState & state, DrvInfos & elems,
-    const Path & profile, bool keepDerivations,
-    const string & lockToken)
-{
-    /* Build the components in the user environment, if they don't
-       exist already. */
-    PathSet drvsToBuild;
-    foreach (DrvInfos::const_iterator, i, elems)
-        /* Call to `isDerivation' is for compatibility with Nix <= 0.7
-           user environments. */
-        if (i->queryDrvPath(state) != "" &&
-            isDerivation(i->queryDrvPath(state)))
-            drvsToBuild.insert(i->queryDrvPath(state));
-
-    debug(format("building user environment dependencies"));
-    store->buildDerivations(drvsToBuild);
-
-    /* Get the environment builder expression. */
-    Expr envBuilder = parseExprFromFile(state,
-        nixDataDir + "/nix/corepkgs/buildenv"); /* !!! */
-
-    /* Construct the whole top level derivation. */
-    PathSet references;
-    ATermList manifest = ATempty;
-    ATermList inputs = ATempty;
-    foreach (DrvInfos::iterator, i, elems) {
-        /* Create a pseudo-derivation containing the name, system,
-           output path, and optionally the derivation path, as well as
-           the meta attributes. */
-        Path drvPath = keepDerivations ? i->queryDrvPath(state) : "";
-
-        /* Round trip to get rid of "bad" meta values (like
-           functions). */
-        MetaInfo meta = i->queryMetaInfo(state);
-        i->setMetaInfo(meta);
-        
-        ATermList as = ATmakeList5(
-            makeBind(toATerm("type"),
-                makeStr("derivation"), makeNoPos()),
-            makeBind(toATerm("name"),
-                makeStr(i->name), makeNoPos()),
-            makeBind(toATerm("system"),
-                makeStr(i->system), makeNoPos()),
-            makeBind(toATerm("outPath"),
-                makeStr(i->queryOutPath(state)), makeNoPos()), 
-            makeBind(toATerm("meta"),
-                i->attrs->get(toATerm("meta")), makeNoPos()));
-        
-        if (drvPath != "") as = ATinsert(as, 
-            makeBind(toATerm("drvPath"),
-                makeStr(drvPath), makeNoPos()));
-        
-        manifest = ATinsert(manifest, makeAttrs(as));
-        
-        inputs = ATinsert(inputs, makeStr(i->queryOutPath(state)));
-
-        /* This is only necessary when installing store paths, e.g.,
-           `nix-env -i /nix/store/abcd...-foo'. */
-        store->addTempRoot(i->queryOutPath(state));
-        store->ensurePath(i->queryOutPath(state));
-        
-        references.insert(i->queryOutPath(state));
-        if (drvPath != "") references.insert(drvPath);
-    }
-
-    /* Also write a copy of the list of inputs to the store; we need
-       it for future modifications of the environment. */
-    Path manifestFile = store->addTextToStore("env-manifest",
-        atPrint(canonicaliseExpr(makeList(ATreverse(manifest)))), references);
-
-    Expr topLevel = makeCall(envBuilder, makeAttrs(ATmakeList3(
-        makeBind(toATerm("system"),
-            makeStr(thisSystem), makeNoPos()),
-        makeBind(toATerm("derivations"),
-            makeList(ATreverse(manifest)), makeNoPos()),
-        makeBind(toATerm("manifest"),
-            makeStr(manifestFile, singleton<PathSet>(manifestFile)), makeNoPos())
-        )));
-
-    /* Instantiate it. */
-    debug(format("evaluating builder expression `%1%'") % topLevel);
-    DrvInfo topLevelDrv;
-    if (!getDerivation(state, topLevel, topLevelDrv))
-        abort();
-    
-    /* Realise the resulting store expression. */
-    debug(format("building user environment"));
-    store->buildDerivations(singleton<PathSet>(topLevelDrv.queryDrvPath(state)));
-
-    /* Switch the current user environment to the output path. */
-    PathLocks lock;
-    lockProfile(lock, profile);
-
-    Path lockTokenCur = optimisticLockProfile(profile);
-    if (lockToken != lockTokenCur) {
-        printMsg(lvlError, format("profile `%1%' changed while we were busy; restarting") % profile);
-        return false;
-    }
-    
-    debug(format("switching to new user environment"));
-    Path generation = createGeneration(profile, topLevelDrv.queryOutPath(state));
-    switchLink(profile, generation);
-
-    return true;
-}
-
-
 static int getPriority(EvalState & state, const DrvInfo & drv)
 {
     MetaValue value = drv.queryMetaInfo(state, "priority");
@@ -516,14 +351,13 @@ static void queryInstSources(EvalState & state,
            (import ./foo.nix)' = `(import ./foo.nix).bar'. */
         case srcNixExprs: {
                 
-            Expr e1 = loadSourceExpr(state, instSource.nixExprPath);
+            Expr * e1 = loadSourceExpr(state, instSource.nixExprPath);
 
-            for (Strings::const_iterator i = args.begin();
-                 i != args.end(); ++i)
-            {
-                Expr e2 = parseExprFromString(state, *i, absPath("."));
-                Expr call = makeCall(e2, e1);
-                getDerivations(state, call, "", instSource.autoArgs, elems);
+            foreach (Strings::const_iterator, i, args) {
+                Expr * e2 = parseExprFromString(state, *i, absPath("."));
+                Expr * call = new ExprApp(e2, e1);
+                Value v; state.eval(call, v);
+                getDerivations(state, v, "", instSource.autoArgs, elems);
             }
             
             break;
@@ -540,7 +374,7 @@ static void queryInstSources(EvalState & state,
                 Path path = followLinksToStorePath(*i);
 
                 DrvInfo elem;
-                elem.attrs = boost::shared_ptr<ATermMap>(new ATermMap(0)); /* ugh... */
+                elem.attrs = new Bindings;
                 string name = baseNameOf(path);
                 string::size_type dash = name.find('-');
                 if (dash != string::npos)
@@ -574,12 +408,12 @@ static void queryInstSources(EvalState & state,
         }
 
         case srcAttrPath: {
-            for (Strings::const_iterator i = args.begin();
-                 i != args.end(); ++i)
-                getDerivations(state,
-                    findAlongAttrPath(state, *i, instSource.autoArgs,
-                        loadSourceExpr(state, instSource.nixExprPath)),
-                    "", instSource.autoArgs, elems);
+            foreach (Strings::const_iterator, i, args) {
+                Value v;
+                findAlongAttrPath(state, *i, instSource.autoArgs,
+                    loadSourceExpr(state, instSource.nixExprPath), v);
+                getDerivations(state, v, "", instSource.autoArgs, elems);
+            }
             break;
         }
     }
@@ -1102,6 +936,7 @@ static void opQuery(Globals & globals,
     
     foreach (vector<DrvInfo>::iterator, i, elems2) {
         try {
+            startNest(nest, lvlDebug, format("outputting query result `%1%'") % i->attrPath);
 
             /* For table output. */
             Strings columns;
@@ -1472,7 +1307,7 @@ void run(Strings args)
 
     op(globals, remaining, opFlags, opArgs);
 
-    printEvalStats(globals.state);
+    globals.state.printStats();
 }
 
 
diff --git a/src/nix-env/profiles.cc b/src/nix-env/profiles.cc
index 75585b1b2..60576f1ae 100644
--- a/src/nix-env/profiles.cc
+++ b/src/nix-env/profiles.cc
@@ -130,6 +130,20 @@ void switchLink(Path link, Path target)
         throw SysError(format("renaming `%1%' to `%2%'") % tmp % link);
 }
 
- 
+
+void lockProfile(PathLocks & lock, const Path & profile)
+{
+    lock.lockPaths(singleton<PathSet>(profile),
+        (format("waiting for lock on profile `%1%'") % profile).str());
+    lock.setDeletion(true);
+}
+
+
+string optimisticLockProfile(const Path & profile)
+{
+    return pathExists(profile) ? readLink(profile) : "";
+}
+
+
 }
 
diff --git a/src/nix-env/profiles.hh b/src/nix-env/profiles.hh
index 99c20f42d..a64258dae 100644
--- a/src/nix-env/profiles.hh
+++ b/src/nix-env/profiles.hh
@@ -2,6 +2,7 @@
 #define __PROFILES_H
 
 #include "types.hh"
+#include "pathlocks.hh"
 
 #include <time.h>
 
@@ -37,6 +38,20 @@ void deleteGeneration(const Path & profile, unsigned int gen);
 
 void switchLink(Path link, Path target);
 
+/* Ensure exclusive access to a profile.  Any command that modifies
+   the profile first acquires this lock. */
+void lockProfile(PathLocks & lock, const Path & profile);
+
+/* Optimistic locking is used by long-running operations like `nix-env
+   -i'.  Instead of acquiring the exclusive lock for the entire
+   duration of the operation, we just perform the operation
+   optimistically (without an exclusive lock), and check at the end
+   whether the profile changed while we were busy (i.e., the symlink
+   target changed).  If so, the operation is restarted.  Restarting is
+   generally cheap, since the build results are still in the Nix
+   store.  Most of the time, only the user environment has to be
+   rebuilt. */
+string optimisticLockProfile(const Path & profile);
 
 }
 
diff --git a/src/nix-env/user-env.cc b/src/nix-env/user-env.cc
new file mode 100644
index 000000000..72e13fceb
--- /dev/null
+++ b/src/nix-env/user-env.cc
@@ -0,0 +1,257 @@
+#include "util.hh"
+#include "get-drvs.hh"
+#include "derivations.hh"
+#include "store-api.hh"
+#include "globals.hh"
+#include "shared.hh"
+#include "eval.hh"
+#include "parser.hh"
+#include "profiles.hh"
+
+
+namespace nix {
+
+
+static void readLegacyManifest(const Path & path, DrvInfos & elems);
+
+
+DrvInfos queryInstalled(EvalState & state, const Path & userEnv)
+{
+    DrvInfos elems;
+
+    Path manifestFile = userEnv + "/manifest.nix";
+    Path oldManifestFile = userEnv + "/manifest";
+
+    if (pathExists(manifestFile)) {
+        Value v;
+        state.eval(parseExprFromFile(state, manifestFile), v);
+        getDerivations(state, v, "", Bindings(), elems);
+    } else if (pathExists(oldManifestFile))
+        readLegacyManifest(oldManifestFile, elems);
+
+    return elems;
+}
+
+
+bool createUserEnv(EvalState & state, DrvInfos & elems,
+    const Path & profile, bool keepDerivations,
+    const string & lockToken)
+{
+    /* Build the components in the user environment, if they don't
+       exist already. */
+    PathSet drvsToBuild;
+    foreach (DrvInfos::const_iterator, i, elems)
+        if (i->queryDrvPath(state) != "")
+            drvsToBuild.insert(i->queryDrvPath(state));
+
+    debug(format("building user environment dependencies"));
+    store->buildDerivations(drvsToBuild);
+
+    /* Construct the whole top level derivation. */
+    PathSet references;
+    Value manifest;
+    state.mkList(manifest, elems.size());
+    unsigned int n = 0;
+    foreach (DrvInfos::iterator, i, elems) {
+        /* Create a pseudo-derivation containing the name, system,
+           output path, and optionally the derivation path, as well as
+           the meta attributes. */
+        Path drvPath = keepDerivations ? i->queryDrvPath(state) : "";
+
+        Value & v(*state.allocValues(1));
+        manifest.list.elems[n++] = &v;
+        state.mkAttrs(v);
+
+        mkString((*v.attrs)[state.sType].value, "derivation");
+        mkString((*v.attrs)[state.sName].value, i->name);
+        mkString((*v.attrs)[state.sSystem].value, i->system);
+        mkString((*v.attrs)[state.sOutPath].value, i->queryOutPath(state));
+        if (drvPath != "")
+            mkString((*v.attrs)[state.sDrvPath].value, i->queryDrvPath(state));
+        
+        state.mkAttrs((*v.attrs)[state.sMeta].value);
+        
+        MetaInfo meta = i->queryMetaInfo(state);
+
+        foreach (MetaInfo::const_iterator, j, meta) {
+            Value & v2((*(*v.attrs)[state.sMeta].value.attrs)[state.symbols.create(j->first)].value);
+            switch (j->second.type) {
+                case MetaValue::tpInt: mkInt(v2, j->second.intValue); break;
+                case MetaValue::tpString: mkString(v2, j->second.stringValue); break;
+                case MetaValue::tpStrings: {
+                    state.mkList(v2, j->second.stringValues.size());
+                    unsigned int m = 0;
+                    foreach (Strings::const_iterator, k, j->second.stringValues) {
+                        v2.list.elems[m] = state.allocValues(1);
+                        mkString(*v2.list.elems[m++], *k);
+                    }
+                    break;
+                }
+                default: abort();
+            }
+        }
+    
+        /* This is only necessary when installing store paths, e.g.,
+           `nix-env -i /nix/store/abcd...-foo'. */
+        store->addTempRoot(i->queryOutPath(state));
+        store->ensurePath(i->queryOutPath(state));
+        
+        references.insert(i->queryOutPath(state));
+        if (drvPath != "") references.insert(drvPath);
+    }
+
+    /* Also write a copy of the list of user environment elements to
+       the store; we need it for future modifications of the
+       environment. */
+    Path manifestFile = store->addTextToStore("env-manifest.nix",
+        (format("%1%") % manifest).str(), references);
+
+    printMsg(lvlError, manifestFile);
+
+    /* Get the environment builder expression. */
+    Value envBuilder;
+    state.eval(parseExprFromFile(state, nixDataDir + "/nix/corepkgs/buildenv"), envBuilder);
+
+    /* Construct a Nix expression that calls the user environment
+       builder with the manifest as argument. */
+    Value args, topLevel;
+    state.mkAttrs(args);
+    mkString((*args.attrs)[state.sSystem].value, thisSystem);
+    mkString((*args.attrs)[state.symbols.create("manifest")].value,
+        manifestFile, singleton<PathSet>(manifestFile));
+    (*args.attrs)[state.symbols.create("derivations")].value = manifest;
+    mkApp(topLevel, envBuilder, args);
+        
+    /* Evaluate it. */
+    debug("evaluating user environment builder");
+    DrvInfo topLevelDrv;
+    if (!getDerivation(state, topLevel, topLevelDrv))
+        abort();
+    
+    /* Realise the resulting store expression. */
+    debug("building user environment");
+    store->buildDerivations(singleton<PathSet>(topLevelDrv.queryDrvPath(state)));
+
+    /* Switch the current user environment to the output path. */
+    PathLocks lock;
+    lockProfile(lock, profile);
+
+    Path lockTokenCur = optimisticLockProfile(profile);
+    if (lockToken != lockTokenCur) {
+        printMsg(lvlError, format("profile `%1%' changed while we were busy; restarting") % profile);
+        return false;
+    }
+    
+    debug(format("switching to new user environment"));
+    Path generation = createGeneration(profile, topLevelDrv.queryOutPath(state));
+    switchLink(profile, generation);
+
+    return true;
+}
+
+
+/* Code for parsing manifests in the old textual ATerm format. */
+
+static string parseStr(std::istream & str)
+{
+    expect(str, "Str(");
+    string s = parseString(str);
+    expect(str, ",[])");
+    return s;
+}
+
+
+static string parseWord(std::istream & str)
+{
+    string res;
+    while (isalpha(str.peek()))
+        res += str.get();
+    return res;
+}
+
+
+static MetaInfo parseMeta(std::istream & str)
+{
+    MetaInfo meta;
+
+    expect(str, "Attrs([");
+    while (!endOfList(str)) {
+        expect(str, "Bind(");
+
+        MetaValue value;
+        
+        string name = parseString(str);
+        expect(str, ",");
+
+        string type = parseWord(str);
+
+        if (type == "Str") {
+            expect(str, "(");
+            value.type = MetaValue::tpString;
+            value.stringValue = parseString(str);
+            expect(str, ",[])");
+        }
+
+        else if (type == "List") {
+            expect(str, "([");
+            value.type = MetaValue::tpStrings;
+            while (!endOfList(str))
+                value.stringValues.push_back(parseStr(str));
+            expect(str, ")");
+        }
+
+        else throw Error(format("unexpected token `%1%'") % type);
+
+        expect(str, ",NoPos)");
+        meta[name] = value;
+    }
+    
+    expect(str, ")");
+
+    return meta;
+}
+
+
+static void readLegacyManifest(const Path & path, DrvInfos & elems)
+{
+    string manifest = readFile(path);
+    std::istringstream str(manifest);
+    expect(str, "List([");
+
+    unsigned int n = 0;
+    
+    while (!endOfList(str)) {
+        DrvInfo elem;
+        expect(str, "Attrs([");
+
+        while (!endOfList(str)) {
+            expect(str, "Bind(");
+            string name = parseString(str);
+            expect(str, ",");
+            
+            if (name == "meta") elem.setMetaInfo(parseMeta(str));
+            else {
+                string value = parseStr(str);
+                if (name == "name") elem.name = value;
+                else if (name == "outPath") elem.setOutPath(value);
+                else if (name == "drvPath") elem.setDrvPath(value);
+                else if (name == "system") elem.system = value;
+            }
+
+            expect(str, ",NoPos)");
+        }
+
+        expect(str, ")");
+
+        if (elem.name != "") {
+            elem.attrPath = int2String(n++);
+            elems.push_back(elem);
+        }
+    }
+
+    expect(str, ")");
+}
+
+
+}
+
diff --git a/src/nix-env/user-env.hh b/src/nix-env/user-env.hh
new file mode 100644
index 000000000..4125d8217
--- /dev/null
+++ b/src/nix-env/user-env.hh
@@ -0,0 +1,20 @@
+#ifndef __USER_ENV_H
+#define __USER_ENV_H
+
+#include "get-drvs.hh"
+
+namespace nix {
+
+DrvInfos queryInstalled(EvalState & state, const Path & userEnv);
+
+bool createUserEnv(EvalState & state, DrvInfos & elems,
+    const Path & profile, bool keepDerivations,
+    const string & lockToken);
+
+}
+
+#endif /* !__USER_ENV_H */
+
+
+
+
diff --git a/src/nix-hash/Makefile.am b/src/nix-hash/Makefile.am
index 350aa8ebd..5f84eb34d 100644
--- a/src/nix-hash/Makefile.am
+++ b/src/nix-hash/Makefile.am
@@ -2,7 +2,7 @@ bin_PROGRAMS = nix-hash
 
 nix_hash_SOURCES = nix-hash.cc help.txt
 nix_hash_LDADD = ../libmain/libmain.la ../libstore/libstore.la ../libutil/libutil.la \
- ../boost/format/libformat.la ${aterm_lib} @ADDITIONAL_NETWORK_LIBS@
+ ../boost/format/libformat.la @ADDITIONAL_NETWORK_LIBS@
 
 nix-hash.o: help.txt.hh
 
diff --git a/src/nix-instantiate/Makefile.am b/src/nix-instantiate/Makefile.am
index 3f6671719..a65907a8d 100644
--- a/src/nix-instantiate/Makefile.am
+++ b/src/nix-instantiate/Makefile.am
@@ -3,7 +3,7 @@ bin_PROGRAMS = nix-instantiate
 nix_instantiate_SOURCES = nix-instantiate.cc help.txt
 nix_instantiate_LDADD = ../libmain/libmain.la ../libexpr/libexpr.la \
  ../libstore/libstore.la ../libutil/libutil.la \
- ../boost/format/libformat.la ${aterm_lib} @ADDITIONAL_NETWORK_LIBS@
+ ../boost/format/libformat.la @ADDITIONAL_NETWORK_LIBS@
 
 nix-instantiate.o: help.txt.hh
 
@@ -11,6 +11,5 @@ nix-instantiate.o: help.txt.hh
 	../bin2c/bin2c helpText < $< > $@ || (rm $@ && exit 1)
 
 AM_CXXFLAGS = \
- ${aterm_include} \
  -I$(srcdir)/.. -I$(srcdir)/../libutil -I$(srcdir)/../libstore \
  -I$(srcdir)/../libexpr -I$(srcdir)/../libmain -I../libexpr
diff --git a/src/nix-instantiate/nix-instantiate.cc b/src/nix-instantiate/nix-instantiate.cc
index 21f352f25..4d629ea1b 100644
--- a/src/nix-instantiate/nix-instantiate.cc
+++ b/src/nix-instantiate/nix-instantiate.cc
@@ -7,7 +7,7 @@
 #include "parser.hh"
 #include "get-drvs.hh"
 #include "attr-path.hh"
-#include "expr-to-xml.hh"
+#include "value-to-xml.hh"
 #include "util.hh"
 #include "store-api.hh"
 #include "common-opts.hh"
@@ -23,7 +23,7 @@ void printHelp()
 }
 
 
-static Expr parseStdin(EvalState & state)
+static Expr * parseStdin(EvalState & state)
 {
     startNest(nest, lvlTalkative, format("parsing standard input"));
     string s, s2;
@@ -37,47 +37,41 @@ static int rootNr = 0;
 static bool indirectRoot = false;
 
 
-static void printResult(EvalState & state, Expr e,
-    bool evalOnly, bool xmlOutput, bool location, const ATermMap & autoArgs)
-{
-    PathSet context;
-    
-    if (evalOnly)
-        if (xmlOutput)
-            printTermAsXML(e, std::cout, context, location);
-        else
-            std::cout << format("%1%\n") % canonicaliseExpr(e);
-    
-    else {
-        DrvInfos drvs;
-        getDerivations(state, e, "", autoArgs, drvs);
-        for (DrvInfos::iterator i = drvs.begin(); i != drvs.end(); ++i) {
-            Path drvPath = i->queryDrvPath(state);
-            if (gcRoot == "")
-                printGCWarning();
-            else
-                drvPath = addPermRoot(drvPath,
-                    makeRootName(gcRoot, rootNr),
-                    indirectRoot);
-            std::cout << format("%1%\n") % drvPath;
-        }
-    }
-}
-
-
 void processExpr(EvalState & state, const Strings & attrPaths,
-    bool parseOnly, bool strict, const ATermMap & autoArgs,
-    bool evalOnly, bool xmlOutput, bool location, Expr e)
+    bool parseOnly, bool strict, const Bindings & autoArgs,
+    bool evalOnly, bool xmlOutput, bool location, Expr * e)
 {
-    for (Strings::const_iterator i = attrPaths.begin(); i != attrPaths.end(); ++i) {
-        Expr e2 = findAlongAttrPath(state, *i, autoArgs, e);
-        if (!parseOnly)
-            if (strict)
-                e2 = strictEvalExpr(state, e2);
-            else
-                e2 = evalExpr(state, e2);
-        printResult(state, e2, evalOnly, xmlOutput, location, autoArgs);
-    }
+    if (parseOnly)
+        std::cout << format("%1%\n") % *e;
+    else
+        foreach (Strings::const_iterator, i, attrPaths) {
+            Value v;
+            findAlongAttrPath(state, *i, autoArgs, e, v);
+            state.forceValue(v);
+
+            PathSet context;
+            if (evalOnly)
+                if (xmlOutput)
+                    printValueAsXML(state, strict, location, v, std::cout, context);
+                else {
+                    if (strict) state.strictForceValue(v);
+                    std::cout << v << std::endl;
+                }
+            else {
+                DrvInfos drvs;
+                getDerivations(state, v, "", autoArgs, drvs);
+                foreach (DrvInfos::iterator, i, drvs) {
+                    Path drvPath = i->queryDrvPath(state);
+                    if (gcRoot == "")
+                        printGCWarning();
+                    else
+                        drvPath = addPermRoot(drvPath,
+                            makeRootName(gcRoot, rootNr),
+                            indirectRoot);
+                    std::cout << format("%1%\n") % drvPath;
+                }
+            }
+        }
 }
 
 
@@ -92,11 +86,9 @@ void run(Strings args)
     bool xmlOutputSourceLocation = true;
     bool strict = false;
     Strings attrPaths;
-    ATermMap autoArgs(128);
+    Bindings autoArgs;
 
-    for (Strings::iterator i = args.begin();
-         i != args.end(); )
-    {
+    for (Strings::iterator i = args.begin(); i != args.end(); ) {
         string arg = *i++;
 
         if (arg == "-")
@@ -140,21 +132,19 @@ void run(Strings args)
     store = openStore();
 
     if (readStdin) {
-        Expr e = parseStdin(state);
+        Expr * e = parseStdin(state);
         processExpr(state, attrPaths, parseOnly, strict, autoArgs,
             evalOnly, xmlOutput, xmlOutputSourceLocation, e);
     }
 
-    for (Strings::iterator i = files.begin();
-         i != files.end(); i++)
-    {
+    foreach (Strings::iterator, i, files) {
         Path path = absPath(*i);
-        Expr e = parseExprFromFile(state, path);
+        Expr * e = parseExprFromFile(state, path);
         processExpr(state, attrPaths, parseOnly, strict, autoArgs,
             evalOnly, xmlOutput, xmlOutputSourceLocation, e);
     }
 
-    printEvalStats(state);
+    state.printStats();
 }
 
 
diff --git a/src/nix-setuid-helper/Makefile.am b/src/nix-setuid-helper/Makefile.am
index a0fbdf39d..35528458c 100644
--- a/src/nix-setuid-helper/Makefile.am
+++ b/src/nix-setuid-helper/Makefile.am
@@ -2,7 +2,7 @@ libexec_PROGRAMS = nix-setuid-helper
 
 nix_setuid_helper_SOURCES = nix-setuid-helper.cc
 nix_setuid_helper_LDADD = ../libutil/libutil.la \
- ../boost/format/libformat.la ${aterm_lib}
+ ../boost/format/libformat.la
 
 AM_CXXFLAGS = \
- -I$(srcdir)/.. $(aterm_include) -I$(srcdir)/../libutil
+ -I$(srcdir)/.. -I$(srcdir)/../libutil
diff --git a/src/nix-store/Makefile.am b/src/nix-store/Makefile.am
index ca0fec570..9a439dd92 100644
--- a/src/nix-store/Makefile.am
+++ b/src/nix-store/Makefile.am
@@ -2,7 +2,7 @@ bin_PROGRAMS = nix-store
 
 nix_store_SOURCES = nix-store.cc dotgraph.cc dotgraph.hh help.txt
 nix_store_LDADD = ../libmain/libmain.la ../libstore/libstore.la ../libutil/libutil.la \
- ../boost/format/libformat.la ${aterm_lib} @ADDITIONAL_NETWORK_LIBS@
+ ../boost/format/libformat.la @ADDITIONAL_NETWORK_LIBS@
 
 nix-store.o: help.txt.hh
 
@@ -10,5 +10,5 @@ nix-store.o: help.txt.hh
 	../bin2c/bin2c helpText < $< > $@ || (rm $@ && exit 1)
 
 AM_CXXFLAGS = \
- -I$(srcdir)/.. $(aterm_include) -I$(srcdir)/../libutil \
+ -I$(srcdir)/.. -I$(srcdir)/../libutil \
  -I$(srcdir)/../libstore -I$(srcdir)/../libmain
diff --git a/src/nix-worker/Makefile.am b/src/nix-worker/Makefile.am
index d1163ce37..50c8ae36d 100644
--- a/src/nix-worker/Makefile.am
+++ b/src/nix-worker/Makefile.am
@@ -2,7 +2,7 @@ bin_PROGRAMS = nix-worker
 
 nix_worker_SOURCES = nix-worker.cc help.txt
 nix_worker_LDADD = ../libmain/libmain.la ../libstore/libstore.la ../libutil/libutil.la \
- ../boost/format/libformat.la ${aterm_lib} @ADDITIONAL_NETWORK_LIBS@
+ ../boost/format/libformat.la @ADDITIONAL_NETWORK_LIBS@
 
 nix-worker.o: help.txt.hh
 
@@ -10,5 +10,5 @@ nix-worker.o: help.txt.hh
 	../bin2c/bin2c helpText < $< > $@ || (rm $@ && exit 1)
 
 AM_CXXFLAGS = \
- -I$(srcdir)/.. $(aterm_include) -I$(srcdir)/../libutil \
+ -I$(srcdir)/.. -I$(srcdir)/../libutil \
  -I$(srcdir)/../libstore -I$(srcdir)/../libmain
diff --git a/substitute.mk b/substitute.mk
index 729116477..50d63ef5c 100644
--- a/substitute.mk
+++ b/substitute.mk
@@ -24,7 +24,6 @@
 	 -e "s^@xmllint\@^$(xmllint)^g" \
 	 -e "s^@xmlflags\@^$(xmlflags)^g" \
 	 -e "s^@xsltproc\@^$(xsltproc)^g" \
-	 -e "s^@aterm_bin\@^$(aterm_bin)^g" \
 	 -e "s^@version\@^$(VERSION)^g" \
 	 -e "s^@testPath\@^$(coreutils):$$(dirname $$(type -P expr))^g" \
 	 < $< > $@ || rm $@
diff --git a/tests/common.sh.in b/tests/common.sh.in
index 85dd3a389..b30bc44b5 100644
--- a/tests/common.sh.in
+++ b/tests/common.sh.in
@@ -30,7 +30,6 @@ export REAL_STORE_DIR=@storedir@
 export NIX_BUILD_HOOK=
 export PERL=perl
 export TOP=$(pwd)/..
-export aterm_bin=@aterm_bin@
 export bzip2_bin_test="@bzip2_bin_test@"
 if test "${bzip2_bin_test:0:1}" != "/"; then
     bzip2_bin_test=`pwd`/${bzip2_bin_test}
@@ -41,10 +40,6 @@ export xmlflags="@xmlflags@"
 export xsltproc="@xsltproc@"
 export SHELL="@shell@"
 
-# Hack to get "atdiff" to run on Cygwin (Windows looks for
-# DLLs in $PATH).
-export PATH=$aterm_bin/../lib:$PATH
-
 export version=@version@
 export system=@system@
 
diff --git a/tests/dependencies.nix b/tests/dependencies.nix
index a397e1ce4..00717ae98 100644
--- a/tests/dependencies.nix
+++ b/tests/dependencies.nix
@@ -9,7 +9,7 @@ let {
 
   input2 = mkDerivation {
     name = "dependencies-input-2";
-    builder = ./. ~ "dependencies.builder2.sh";
+    builder = ./dependencies.builder2.sh;
   };
 
   body = mkDerivation {
diff --git a/tests/lang.sh b/tests/lang.sh
index 54f010763..fab8c6e0d 100644
--- a/tests/lang.sh
+++ b/tests/lang.sh
@@ -16,14 +16,10 @@ done
 for i in lang/parse-okay-*.nix; do
     echo "parsing $i (should succeed)";
     i=$(basename $i .nix)
-    if ! $nixinstantiate --parse-only - < lang/$i.nix > lang/$i.ast; then
+    if ! $nixinstantiate --parse-only - < lang/$i.nix > lang/$i.out; then
         echo "FAIL: $i should parse"
         fail=1
     fi
-    if ! $aterm_bin/atdiff lang/$i.ast lang/$i.exp; then
-        echo "FAIL: parse tree of $i not as expected"
-        fail=1
-    fi
 done
 
 for i in lang/eval-fail-*.nix; do
@@ -44,10 +40,10 @@ for i in lang/eval-okay-*.nix; do
         if test -e lang/$i.flags; then
             flags=$(cat lang/$i.flags)
         fi
-        if ! $nixinstantiate $flags --eval-only lang/$i.nix > lang/$i.out; then
+        if ! $nixinstantiate $flags --eval-only --strict lang/$i.nix > lang/$i.out; then
             echo "FAIL: $i should evaluate"
             fail=1
-        elif ! $aterm_bin/atdiff lang/$i.out lang/$i.exp; then
+        elif ! diff lang/$i.out lang/$i.exp; then
             echo "FAIL: evaluation result of $i not as expected"
             fail=1
         fi
diff --git a/tests/lang/eval-okay-arithmetic.exp b/tests/lang/eval-okay-arithmetic.exp
index 433cb1c9b..9c113c6f7 100644
--- a/tests/lang/eval-okay-arithmetic.exp
+++ b/tests/lang/eval-okay-arithmetic.exp
@@ -1 +1 @@
-Int(1275)
+1275
diff --git a/tests/lang/eval-okay-attrnames.exp b/tests/lang/eval-okay-attrnames.exp
index 98af99a0c..b4aa387e0 100644
--- a/tests/lang/eval-okay-attrnames.exp
+++ b/tests/lang/eval-okay-attrnames.exp
@@ -1 +1 @@
-Str("newxfoonewxy",[])
+"newxfoonewxy"
diff --git a/tests/lang/eval-okay-attrs.exp b/tests/lang/eval-okay-attrs.exp
index add36384d..45b0f829e 100644
--- a/tests/lang/eval-okay-attrs.exp
+++ b/tests/lang/eval-okay-attrs.exp
@@ -1 +1 @@
-Int(987)
\ No newline at end of file
+987
diff --git a/tests/lang/eval-okay-attrs2.exp b/tests/lang/eval-okay-attrs2.exp
index add36384d..45b0f829e 100644
--- a/tests/lang/eval-okay-attrs2.exp
+++ b/tests/lang/eval-okay-attrs2.exp
@@ -1 +1 @@
-Int(987)
\ No newline at end of file
+987
diff --git a/tests/lang/eval-okay-attrs3.exp b/tests/lang/eval-okay-attrs3.exp
index d2c7555c1..19de4fdf7 100644
--- a/tests/lang/eval-okay-attrs3.exp
+++ b/tests/lang/eval-okay-attrs3.exp
@@ -1 +1 @@
-Str("foo 22 80 itchyxac",[])
+"foo 22 80 itchyxac"
diff --git a/tests/lang/eval-okay-autoargs.exp b/tests/lang/eval-okay-autoargs.exp
index 3b12bdd5e..7a8391786 100644
--- a/tests/lang/eval-okay-autoargs.exp
+++ b/tests/lang/eval-okay-autoargs.exp
@@ -1 +1 @@
-Str("xyzzy!xyzzy!foobar",[])
+"xyzzy!xyzzy!foobar"
diff --git a/tests/lang/eval-okay-builtins.exp b/tests/lang/eval-okay-builtins.exp
index f4f3ba81a..0661686d6 100644
--- a/tests/lang/eval-okay-builtins.exp
+++ b/tests/lang/eval-okay-builtins.exp
@@ -1 +1 @@
-Path("/foo")
+/foo
diff --git a/tests/lang/eval-okay-concat.exp b/tests/lang/eval-okay-concat.exp
index 359ccef86..bb4bbd577 100644
--- a/tests/lang/eval-okay-concat.exp
+++ b/tests/lang/eval-okay-concat.exp
@@ -1 +1 @@
-List([Int(1),Int(2),Int(3),Int(4),Int(5),Int(6),Int(7),Int(8),Int(9)])
+[ 1 2 3 4 5 6 7 8 9 ]
diff --git a/tests/lang/eval-okay-context.exp b/tests/lang/eval-okay-context.exp
index 95a993654..2f535bdbc 100644
--- a/tests/lang/eval-okay-context.exp
+++ b/tests/lang/eval-okay-context.exp
@@ -1 +1 @@
-Str("foo eval-okay-context.nix bar",[])
+"foo eval-okay-context.nix bar"
diff --git a/tests/lang/eval-okay-empty-args.exp b/tests/lang/eval-okay-empty-args.exp
index c386bbc80..cb5537d5d 100644
--- a/tests/lang/eval-okay-empty-args.exp
+++ b/tests/lang/eval-okay-empty-args.exp
@@ -1 +1 @@
-Str("ab",[])
+"ab"
diff --git a/tests/lang/eval-okay-flatten.exp b/tests/lang/eval-okay-flatten.exp
index 50c91bee5..b979b2b8b 100644
--- a/tests/lang/eval-okay-flatten.exp
+++ b/tests/lang/eval-okay-flatten.exp
@@ -1 +1 @@
-Str("1234567",[])
+"1234567"
diff --git a/tests/lang/eval-okay-getenv.exp b/tests/lang/eval-okay-getenv.exp
index 7c3659b97..14e24d419 100644
--- a/tests/lang/eval-okay-getenv.exp
+++ b/tests/lang/eval-okay-getenv.exp
@@ -1 +1 @@
-Str("foobar",[])
+"foobar"
diff --git a/tests/lang/eval-okay-if.exp b/tests/lang/eval-okay-if.exp
index 8b99801d3..00750edc0 100644
--- a/tests/lang/eval-okay-if.exp
+++ b/tests/lang/eval-okay-if.exp
@@ -1 +1 @@
-Int(3)
\ No newline at end of file
+3
diff --git a/tests/lang/eval-okay-ind-string.exp b/tests/lang/eval-okay-ind-string.exp
index b8d2f5b39..886219dcf 100644
--- a/tests/lang/eval-okay-ind-string.exp
+++ b/tests/lang/eval-okay-ind-string.exp
@@ -1 +1 @@
-Str("This is an indented multi-line string\nliteral.  An amount of whitespace at\nthe start of each line matching the minimum\nindentation of all lines in the string\nliteral together will be removed.  Thus,\nin this case four spaces will be\nstripped from each line, even though\n  THIS LINE is indented six spaces.\n\nAlso, empty lines don't count in the\ndetermination of the indentation level (the\nprevious empty line has indentation 0, but\nit doesn't matter).\nIf the string starts with whitespace\n  followed by a newline, it's stripped, but\n  that's not the case here. Two spaces are\n  stripped because of the \"  \" at the start. \nThis line is indented\na bit further.\nAnti-quotations, like so, are\nalso allowed.\n  The \\ is not special here.\n' can be followed by any character except another ', e.g. 'x'.\nLikewise for $, e.g. $$ or $varName.\nBut ' followed by ' is special, as is $ followed by {.\nIf you want them, use anti-quotations: '', ${.\n   Tabs are not interpreted as whitespace (since we can't guess\n   what tab settings are intended), so don't use them.\n\tThis line starts with a space and a tab, so only one\n   space will be stripped from each line.\nAlso note that if the last line (just before the closing ' ')\nconsists only of whitespace, it's ignored.  But here there is\nsome non-whitespace stuff, so the line isn't removed. \nThis shows a hacky way to preserve an empty line after the start.\nBut there's no reason to do so: you could just repeat the empty\nline.\n  Similarly you can force an indentation level,\n  in this case to 2 spaces.  This works because the anti-quote\n  is significant (not whitespace).\nstart on network-interfaces\n\nstart script\n\n  rm -f /var/run/opengl-driver\n  ln -sf 123 /var/run/opengl-driver\n\n  rm -f /var/log/slim.log\n   \nend script\n\nenv SLIM_CFGFILE=abc\nenv SLIM_THEMESDIR=def\nenv FONTCONFIG_FILE=/etc/fonts/fonts.conf  \t\t\t\t# !!! cleanup\nenv XKB_BINDIR=foo/bin         \t\t\t\t# Needed for the Xkb extension.\nenv LD_LIBRARY_PATH=libX11/lib:libXext/lib:/usr/lib/          # related to xorg-sys-opengl - needed to load libglx for (AI)GLX support (for compiz)\n\nenv XORG_DRI_DRIVER_PATH=nvidiaDrivers/X11R6/lib/modules/drivers/ \n\nexec slim/bin/slim\nEscaping of ' followed by ': ''\nEscaping of $ followed by {: ${\nAnd finally to interpret \\n etc. as in a string: \n, \r, \t.\nfoo\n'bla'\nbar\n",[])
+"This is an indented multi-line string\nliteral.  An amount of whitespace at\nthe start of each line matching the minimum\nindentation of all lines in the string\nliteral together will be removed.  Thus,\nin this case four spaces will be\nstripped from each line, even though\n  THIS LINE is indented six spaces.\n\nAlso, empty lines don't count in the\ndetermination of the indentation level (the\nprevious empty line has indentation 0, but\nit doesn't matter).\nIf the string starts with whitespace\n  followed by a newline, it's stripped, but\n  that's not the case here. Two spaces are\n  stripped because of the \"  \" at the start. \nThis line is indented\na bit further.\nAnti-quotations, like so, are\nalso allowed.\n  The \\ is not special here.\n' can be followed by any character except another ', e.g. 'x'.\nLikewise for $, e.g. $$ or $varName.\nBut ' followed by ' is special, as is $ followed by {.\nIf you want them, use anti-quotations: '', ${.\n   Tabs are not interpreted as whitespace (since we can't guess\n   what tab settings are intended), so don't use them.\n\tThis line starts with a space and a tab, so only one\n   space will be stripped from each line.\nAlso note that if the last line (just before the closing ' ')\nconsists only of whitespace, it's ignored.  But here there is\nsome non-whitespace stuff, so the line isn't removed. \nThis shows a hacky way to preserve an empty line after the start.\nBut there's no reason to do so: you could just repeat the empty\nline.\n  Similarly you can force an indentation level,\n  in this case to 2 spaces.  This works because the anti-quote\n  is significant (not whitespace).\nstart on network-interfaces\n\nstart script\n\n  rm -f /var/run/opengl-driver\n  ln -sf 123 /var/run/opengl-driver\n\n  rm -f /var/log/slim.log\n   \nend script\n\nenv SLIM_CFGFILE=abc\nenv SLIM_THEMESDIR=def\nenv FONTCONFIG_FILE=/etc/fonts/fonts.conf  \t\t\t\t# !!! cleanup\nenv XKB_BINDIR=foo/bin         \t\t\t\t# Needed for the Xkb extension.\nenv LD_LIBRARY_PATH=libX11/lib:libXext/lib:/usr/lib/          # related to xorg-sys-opengl - needed to load libglx for (AI)GLX support (for compiz)\n\nenv XORG_DRI_DRIVER_PATH=nvidiaDrivers/X11R6/lib/modules/drivers/ \n\nexec slim/bin/slim\nEscaping of ' followed by ': ''\nEscaping of $ followed by {: ${\nAnd finally to interpret \\n etc. as in a string: \n, \r, \t.\nfoo\n'bla'\nbar\n"
diff --git a/tests/lang/eval-okay-let.exp b/tests/lang/eval-okay-let.exp
index 7c3659b97..14e24d419 100644
--- a/tests/lang/eval-okay-let.exp
+++ b/tests/lang/eval-okay-let.exp
@@ -1 +1 @@
-Str("foobar",[])
+"foobar"
diff --git a/tests/lang/eval-okay-list.exp b/tests/lang/eval-okay-list.exp
index b9cad67dd..f784f26d8 100644
--- a/tests/lang/eval-okay-list.exp
+++ b/tests/lang/eval-okay-list.exp
@@ -1 +1 @@
-Str("foobarblatest",[])
+"foobarblatest"
diff --git a/tests/lang/eval-okay-listToAttrs.out b/tests/lang/eval-okay-listToAttrs.out
deleted file mode 100644
index 4e779ff06..000000000
--- a/tests/lang/eval-okay-listToAttrs.out
+++ /dev/null
@@ -1 +0,0 @@
-List([Attrs([Bind("a",Str("A",[]),NoPos),Bind("b",Str("B",[]),NoPos)]),Attrs([Bind("a",Str("A",[]),NoPos),Bind("b",Str("B",[]),NoPos)])])
diff --git a/tests/lang/eval-okay-listtoattrs.exp b/tests/lang/eval-okay-listtoattrs.exp
new file mode 100644
index 000000000..11d29b588
--- /dev/null
+++ b/tests/lang/eval-okay-listtoattrs.exp
@@ -0,0 +1 @@
+"AA"
diff --git a/tests/lang/eval-okay-listToAttrs.nix b/tests/lang/eval-okay-listtoattrs.nix
index f5eae92cc..d5cd726b0 100644
--- a/tests/lang/eval-okay-listToAttrs.nix
+++ b/tests/lang/eval-okay-listtoattrs.nix
@@ -1,8 +1,10 @@
 # this test shows how to use listToAttrs and that evaluation is still lazy (throw isn't called)
+with import ./lib.nix;
+
 let 
-  asi = attr: value : { inherit attr value; };
+  asi = name: value : { inherit name value; };
   list = [ ( asi "a" "A" ) ( asi "b" "B" ) ];
   a = builtins.listToAttrs list;
   b = builtins.listToAttrs ( list ++ list );
   r = builtins.listToAttrs [ (asi "result" [ a b ]) ( asi "throw" (throw "this should not be thrown")) ];
-in r.result
+in concat (map (x: x.a) r.result)
diff --git a/tests/lang/eval-okay-logic.exp b/tests/lang/eval-okay-logic.exp
index f1161b8d5..d00491fd7 100644
--- a/tests/lang/eval-okay-logic.exp
+++ b/tests/lang/eval-okay-logic.exp
@@ -1 +1 @@
-Int(1)
\ No newline at end of file
+1
diff --git a/tests/lang/eval-okay-map.exp b/tests/lang/eval-okay-map.exp
index 2d9456dc0..dbb64f717 100644
--- a/tests/lang/eval-okay-map.exp
+++ b/tests/lang/eval-okay-map.exp
@@ -1 +1 @@
-Str("foobarblabarxyzzybar",[])
+"foobarblabarxyzzybar"
diff --git a/tests/lang/eval-okay-new-let.exp b/tests/lang/eval-okay-new-let.exp
index f10a34e71..f98b38807 100644
--- a/tests/lang/eval-okay-new-let.exp
+++ b/tests/lang/eval-okay-new-let.exp
@@ -1 +1 @@
-Str("xyzzyfoobar",[])
+"xyzzyfoobar"
diff --git a/tests/lang/eval-okay-pathexists.exp b/tests/lang/eval-okay-pathexists.exp
index 2015847b6..27ba77dda 100644
--- a/tests/lang/eval-okay-pathexists.exp
+++ b/tests/lang/eval-okay-pathexists.exp
@@ -1 +1 @@
-Bool(True)
+true
diff --git a/tests/lang/eval-okay-patterns.exp b/tests/lang/eval-okay-patterns.exp
index 8422900dd..a4304010f 100644
--- a/tests/lang/eval-okay-patterns.exp
+++ b/tests/lang/eval-okay-patterns.exp
@@ -1 +1 @@
-Str("abcxyzDDDDEFghijk",[])
+"abcxyzDDDDEFijk"
diff --git a/tests/lang/eval-okay-patterns.nix b/tests/lang/eval-okay-patterns.nix
index c233c406c..96fd25a01 100644
--- a/tests/lang/eval-okay-patterns.nix
+++ b/tests/lang/eval-okay-patterns.nix
@@ -6,8 +6,6 @@ let
 
   h = {x ? "d", y ? x, z ? args.x}@args: x + y + z;
 
-  i = args@args2: args.x + args2.y;
-
   j = {x, y, z, ...}: x + y + z;
 
 in
@@ -15,5 +13,4 @@ in
   g {x = "x"; y = "y"; z = "z";} +
   h {x = "D";} +
   h {x = "D"; y = "E"; z = "F";} +
-  i {x = "g"; y = "h";} +
   j {x = "i"; y = "j"; z = "k"; bla = "bla"; foo = "bar";}
diff --git a/tests/lang/eval-okay-readfile.exp b/tests/lang/eval-okay-readfile.exp
index 979771c7a..a2c87d0c4 100644
--- a/tests/lang/eval-okay-readfile.exp
+++ b/tests/lang/eval-okay-readfile.exp
@@ -1 +1 @@
-Str("builtins.readFile ./eval-okay-readfile.nix\n",[])
+"builtins.readFile ./eval-okay-readfile.nix\n"
diff --git a/tests/lang/eval-okay-remove.exp b/tests/lang/eval-okay-remove.exp
index e22e6b1b2..8d38505c1 100644
--- a/tests/lang/eval-okay-remove.exp
+++ b/tests/lang/eval-okay-remove.exp
@@ -1 +1 @@
-Int(456)
+456
diff --git a/tests/lang/eval-okay-scope-1.exp b/tests/lang/eval-okay-scope-1.exp
index 7da0e4219..00750edc0 100644
--- a/tests/lang/eval-okay-scope-1.exp
+++ b/tests/lang/eval-okay-scope-1.exp
@@ -1 +1 @@
-Int(3)
+3
diff --git a/tests/lang/eval-okay-scope-2.exp b/tests/lang/eval-okay-scope-2.exp
index 067d2b746..d00491fd7 100644
--- a/tests/lang/eval-okay-scope-2.exp
+++ b/tests/lang/eval-okay-scope-2.exp
@@ -1 +1 @@
-Int(1)
+1
diff --git a/tests/lang/eval-okay-scope-3.exp b/tests/lang/eval-okay-scope-3.exp
index 65c1faee2..b8626c4cf 100644
--- a/tests/lang/eval-okay-scope-3.exp
+++ b/tests/lang/eval-okay-scope-3.exp
@@ -1 +1 @@
-Int(4)
+4
diff --git a/tests/lang/eval-okay-scope-4.exp b/tests/lang/eval-okay-scope-4.exp
index ea9580603..00ff03a46 100644
--- a/tests/lang/eval-okay-scope-4.exp
+++ b/tests/lang/eval-okay-scope-4.exp
@@ -1 +1 @@
-Str("ccdd",[])
+"ccdd"
diff --git a/tests/lang/eval-okay-scope-6.exp b/tests/lang/eval-okay-scope-6.exp
index ea9580603..00ff03a46 100644
--- a/tests/lang/eval-okay-scope-6.exp
+++ b/tests/lang/eval-okay-scope-6.exp
@@ -1 +1 @@
-Str("ccdd",[])
+"ccdd"
diff --git a/tests/lang/eval-okay-scope-7.exp b/tests/lang/eval-okay-scope-7.exp
index 067d2b746..d00491fd7 100644
--- a/tests/lang/eval-okay-scope-7.exp
+++ b/tests/lang/eval-okay-scope-7.exp
@@ -1 +1 @@
-Int(1)
+1
diff --git a/tests/lang/eval-okay-string.exp b/tests/lang/eval-okay-string.exp
index 8249c7c8d..607920247 100644
--- a/tests/lang/eval-okay-string.exp
+++ b/tests/lang/eval-okay-string.exp
@@ -1 +1 @@
-Str("foobar/a/b/c/d/foo/xyzzy/foo.txt/../foo/x/yescape: \"quote\" \n \\end\nof\nlinefoobarblaatfoo$bar",[])
+"foobar/a/b/c/d/foo/xyzzy/foo.txt/../foo/x/yescape: \"quote\" \n \\end\nof\nlinefoobarblaatfoo$bar"
diff --git a/tests/lang/eval-okay-substring.exp b/tests/lang/eval-okay-substring.exp
index d6098476b..d936b7e96 100644
--- a/tests/lang/eval-okay-substring.exp
+++ b/tests/lang/eval-okay-substring.exp
@@ -1 +1 @@
-Str("ooxfoobarybarzobaabb",[])
+"ooxfoobarybarzobaabb"
diff --git a/tests/lang/eval-okay-to-xml.exp b/tests/lang/eval-okay-to-xml.exp
deleted file mode 100644
index 0a4d1884e..000000000
--- a/tests/lang/eval-okay-to-xml.exp
+++ /dev/null
@@ -1 +0,0 @@
-Str("<?xml version='1.0' encoding='utf-8'?>\n<expr>\n  <list>\n    <string value=\"ab\" />\n    <int value=\"10\" />\n    <attrs>\n      <attr name=\"x\">\n        <string value=\"x\" />\n      </attr>\n      <attr name=\"y\">\n        <string value=\"x\" />\n      </attr>\n    </attrs>\n  </list>\n</expr>\n",[])
diff --git a/tests/lang/eval-okay-toxml.exp b/tests/lang/eval-okay-toxml.exp
index 379f3c076..828220890 100644
--- a/tests/lang/eval-okay-toxml.exp
+++ b/tests/lang/eval-okay-toxml.exp
@@ -1 +1 @@
-Str("<?xml version='1.0' encoding='utf-8'?>\n<expr>\n  <attrs>\n    <attr name=\"a\">\n      <string value=\"s\" />\n    </attr>\n  </attrs>\n</expr>\n",[])
+"<?xml version='1.0' encoding='utf-8'?>\n<expr>\n  <attrs>\n    <attr name=\"a\">\n      <string value=\"s\" />\n    </attr>\n  </attrs>\n</expr>\n"
diff --git a/tests/lang/eval-okay-toxml2.exp b/tests/lang/eval-okay-toxml2.exp
new file mode 100644
index 000000000..634a841eb
--- /dev/null
+++ b/tests/lang/eval-okay-toxml2.exp
@@ -0,0 +1 @@
+"<?xml version='1.0' encoding='utf-8'?>\n<expr>\n  <list>\n    <string value=\"ab\" />\n    <int value=\"10\" />\n    <attrs>\n      <attr name=\"x\">\n        <string value=\"x\" />\n      </attr>\n      <attr name=\"y\">\n        <string value=\"x\" />\n      </attr>\n    </attrs>\n  </list>\n</expr>\n"
diff --git a/tests/lang/eval-okay-to-xml.nix b/tests/lang/eval-okay-toxml2.nix
index ff1791b30..ff1791b30 100644
--- a/tests/lang/eval-okay-to-xml.nix
+++ b/tests/lang/eval-okay-toxml2.nix
diff --git a/tests/lang/eval-okay-tryeval.exp b/tests/lang/eval-okay-tryeval.exp
new file mode 100644
index 000000000..2b2e6fa71
--- /dev/null
+++ b/tests/lang/eval-okay-tryeval.exp
@@ -0,0 +1 @@
+{ x = { success = true; value = "x"; }; y = { success = false; value = false; }; z = { success = false; value = false; }; }
diff --git a/tests/lang/eval-okay-tryeval.nix b/tests/lang/eval-okay-tryeval.nix
new file mode 100644
index 000000000..629bc440a
--- /dev/null
+++ b/tests/lang/eval-okay-tryeval.nix
@@ -0,0 +1,5 @@
+{
+  x = builtins.tryEval "x";
+  y = builtins.tryEval (assert false; "y");
+  z = builtins.tryEval (throw "bla");
+}
diff --git a/tests/lang/eval-okay-versions.exp b/tests/lang/eval-okay-versions.exp
index 2015847b6..27ba77dda 100644
--- a/tests/lang/eval-okay-versions.exp
+++ b/tests/lang/eval-okay-versions.exp
@@ -1 +1 @@
-Bool(True)
+true
diff --git a/tests/lang/eval-okay-with.exp b/tests/lang/eval-okay-with.exp
index 2c9bd8ba0..378c8dc80 100644
--- a/tests/lang/eval-okay-with.exp
+++ b/tests/lang/eval-okay-with.exp
@@ -1 +1 @@
-Str("xyzzybarxyzzybar",[])
+"xyzzybarxyzzybar"
diff --git a/tests/lang/eval-okay-xml.exp.xml b/tests/lang/eval-okay-xml.exp.xml
index 72a96d54c..f124f939e 100644
--- a/tests/lang/eval-okay-xml.exp.xml
+++ b/tests/lang/eval-okay-xml.exp.xml
@@ -6,14 +6,11 @@
     </attr>
     <attr name="at">
       <function>
-        <at>
-          <varpat name="args" />
-          <attrspat>
-            <attr name="x" />
-            <attr name="y" />
-            <attr name="z" />
-          </attrspat>
-        </at>
+        <attrspat name="args">
+          <attr name="x" />
+          <attr name="y" />
+          <attr name="z" />
+        </attrspat>
       </function>
     </attr>
     <attr name="b">
@@ -24,11 +21,10 @@
     </attr>
     <attr name="ellipsis">
       <function>
-        <attrspat>
+        <attrspat ellipsis="1">
           <attr name="x" />
           <attr name="y" />
           <attr name="z" />
-          <ellipsis />
         </attrspat>
       </function>
     </attr>
diff --git a/tests/lang/parse-fail-dup-attrs-7.nix b/tests/lang/parse-fail-dup-attrs-7.nix
new file mode 100644
index 000000000..bbc3eb08c
--- /dev/null
+++ b/tests/lang/parse-fail-dup-attrs-7.nix
@@ -0,0 +1,9 @@
+rec {
+
+  x = 1;
+
+  as = {
+    inherit x;
+    inherit x;
+  };
+}
\ No newline at end of file
diff --git a/tests/lang/parse-okay-1.exp b/tests/lang/parse-okay-1.exp
deleted file mode 100644
index bb8746ec4..000000000
--- a/tests/lang/parse-okay-1.exp
+++ /dev/null
@@ -1 +0,0 @@
-Function(AttrsPat([Formal("x",NoDefaultValue),Formal("y",NoDefaultValue),Formal("z",NoDefaultValue)],Bool(False)),OpPlus(OpPlus(Var("x"),Var("y")),Var("z")),NoPos)
diff --git a/tests/lang/parse-okay-crlf.exp b/tests/lang/parse-okay-crlf.exp
deleted file mode 100644
index 7d4d9e387..000000000
--- a/tests/lang/parse-okay-crlf.exp
+++ /dev/null
@@ -1 +0,0 @@
-Rec([Bind("x",Var("y"),NoPos),Bind("y",Int(123),NoPos),Bind("foo",Str("multi\nline\n  string\n  test\r",[]),NoPos),Bind("z",Int(456),NoPos)],[])
diff --git a/tests/lang/parse-fail-dup-attrs-5.nix b/tests/lang/parse-okay-dup-attrs-5.nix
index f4b9efd0c..f4b9efd0c 100644
--- a/tests/lang/parse-fail-dup-attrs-5.nix
+++ b/tests/lang/parse-okay-dup-attrs-5.nix
diff --git a/tests/lang/parse-okay-regression-20041027.exp b/tests/lang/parse-okay-regression-20041027.exp
deleted file mode 100644
index a302e2488..000000000
--- a/tests/lang/parse-okay-regression-20041027.exp
+++ /dev/null
@@ -1 +0,0 @@
-Function(AttrsPat([Formal("stdenv",NoDefaultValue),Formal("fetchurl",NoDefaultValue)],Bool(False)),Call(Select(Var("stdenv"),"mkDerivation"),Attrs([Bind("name",Str("libXi-6.0.1",[]),NoPos),Bind("src",Call(Var("fetchurl"),Attrs([Bind("md5",Str("7e935a42428d63a387b3c048be0f2756",[]),NoPos),Bind("url",Str("http://freedesktop.org/~xlibs/release/libXi-6.0.1.tar.bz2",[]),NoPos)])),NoPos)])),NoPos)
diff --git a/tests/lang/parse-okay-subversion.exp b/tests/lang/parse-okay-subversion.exp
deleted file mode 100644
index 102153c18..000000000
--- a/tests/lang/parse-okay-subversion.exp
+++ /dev/null
@@ -1 +0,0 @@
-Function(AttrsPat([Formal("localServer",DefaultValue(Var("false"))),Formal("httpServer",DefaultValue(Var("false"))),Formal("sslSupport",DefaultValue(Var("false"))),Formal("pythonBindings",DefaultValue(Var("false"))),Formal("javaSwigBindings",DefaultValue(Var("false"))),Formal("javahlBindings",DefaultValue(Var("false"))),Formal("stdenv",NoDefaultValue),Formal("fetchurl",NoDefaultValue),Formal("openssl",DefaultValue(Var("null"))),Formal("httpd",DefaultValue(Var("null"))),Formal("db4",DefaultValue(Var("null"))),Formal("expat",NoDefaultValue),Formal("swig",DefaultValue(Var("null"))),Formal("j2sdk",DefaultValue(Var("null")))],Bool(False)),Assert(OpNEq(Var("expat"),Var("null")),Assert(OpImpl(Var("localServer"),OpNEq(Var("db4"),Var("null"))),Assert(OpImpl(Var("httpServer"),OpAnd(OpNEq(Var("httpd"),Var("null")),OpEq(Select(Var("httpd"),"expat"),Var("expat")))),Assert(OpImpl(Var("sslSupport"),OpAnd(OpNEq(Var("openssl"),Var("null")),OpImpl(Var("httpServer"),OpEq(Select(Var("httpd"),"openssl"),Var("openssl"))))),Assert(OpImpl(Var("pythonBindings"),OpAnd(OpNEq(Var("swig"),Var("null")),Select(Var("swig"),"pythonSupport"))),Assert(OpImpl(Var("javaSwigBindings"),OpAnd(OpNEq(Var("swig"),Var("null")),Select(Var("swig"),"javaSupport"))),Assert(OpImpl(Var("javahlBindings"),OpNEq(Var("j2sdk"),Var("null"))),Call(Select(Var("stdenv"),"mkDerivation"),Attrs([Bind("builder",Path("/foo/bar"),NoPos),Bind("db4",If(Var("localServer"),Var("db4"),Var("null")),NoPos),Bind("expat",Var("expat"),NoPos),Bind("httpServer",Var("httpServer"),NoPos),Bind("httpd",If(Var("httpServer"),Var("httpd"),Var("null")),NoPos),Bind("j2sdk",If(Var("javaSwigBindings"),Select(Var("swig"),"j2sdk"),If(Var("javahlBindings"),Var("j2sdk"),Var("null"))),NoPos),Bind("javaSwigBindings",Var("javaSwigBindings"),NoPos),Bind("javahlBindings",Var("javahlBindings"),NoPos),Bind("localServer",Var("localServer"),NoPos),Bind("name",Str("subversion-1.1.1",[]),NoPos),Bind("openssl",If(Var("sslSupport"),Var("openssl"),Var("null")),NoPos),Bind("patches",If(Var("javahlBindings"),List([Path("/javahl.patch")]),List([])),NoPos),Bind("python",If(Var("pythonBindings"),Select(Var("swig"),"python"),Var("null")),NoPos),Bind("pythonBindings",Var("pythonBindings"),NoPos),Bind("src",Call(Var("fetchurl"),Attrs([Bind("md5",Str("a180c3fe91680389c210c99def54d9e0",[]),NoPos),Bind("url",Str("http://subversion.tigris.org/tarballs/subversion-1.1.1.tar.bz2",[]),NoPos)])),NoPos),Bind("sslSupport",Var("sslSupport"),NoPos),Bind("swig",If(OpOr(Var("pythonBindings"),Var("javaSwigBindings")),Var("swig"),Var("null")),NoPos)])),NoPos),NoPos),NoPos),NoPos),NoPos),NoPos),NoPos),NoPos)
diff --git a/tests/lang/parse-okay-url.exp b/tests/lang/parse-okay-url.exp
deleted file mode 100644
index 2aa22c379..000000000
--- a/tests/lang/parse-okay-url.exp
+++ /dev/null
@@ -1 +0,0 @@
-List([Str("x:x",[]),Str("https://svn.cs.uu.nl:12443/repos/trace/trunk",[]),Str("http://www2.mplayerhq.hu/MPlayer/releases/fonts/font-arial-iso-8859-1.tar.bz2",[]),Str("http://losser.st-lab.cs.uu.nl/~armijn/.nix/gcc-3.3.4-static-nix.tar.gz",[]),Str("http://fpdownload.macromedia.com/get/shockwave/flash/english/linux/7.0r25/install_flash_player_7_linux.tar.gz",[]),Str("ftp://ftp.gtk.org/pub/gtk/v1.2/gtk+-1.2.10.tar.gz",[])])