11 files changed, 68 insertions, 26 deletions
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 02df4a4a3..3334e4bbd 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -176,6 +176,16 @@ Path evalPath(EvalState & state, Expr e)
 }
 
 
+int evalInt(EvalState & state, Expr e)
+{
+    e = evalExpr(state, e);
+    int i;
+    if (!matchInt(e, i))
+        throw TypeError(format("value is %1% while an integer was expected") % showType(e));
+    return i;
+}
+
+
 bool evalBool(EvalState & state, Expr e)
 {
     e = evalExpr(state, e);
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index b34e91055..a7f4e6943 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -62,6 +62,7 @@ Expr strictEvalExpr(EvalState & state, Expr e,
 /* Specific results. */
 string evalString(EvalState & state, Expr e);
 Path evalPath(EvalState & state, Expr e);
+int evalInt(EvalState & state, Expr e);
 bool evalBool(EvalState & state, Expr e);
 ATermList evalList(EvalState & state, Expr e);
 ATerm coerceToString(Expr e);
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 190d58733..1739b6656 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -771,6 +771,14 @@ static Expr primRelativise(EvalState & state, const ATermVector & args)
 }
 
 
+static Expr primAdd(EvalState & state, const ATermVector & args)
+{
+    int i1 = evalInt(state, args[0]);
+    int i2 = evalInt(state, args[1]);
+    return makeInt(i1 + i2);
+}
+
+
 void EvalState::addPrimOps()
 {
     addPrimOp("builtins", 0, primBuiltins);
@@ -801,6 +809,7 @@ void EvalState::addPrimOps()
     addPrimOp("__hasAttr", 2, primHasAttr);
     addPrimOp("removeAttrs", 2, primRemoveAttrs);
     addPrimOp("relativise", 2, primRelativise);
+    addPrimOp("__add", 2, primAdd);
 }
 
  
diff --git a/tests/lang.sh b/tests/lang.sh
index 6ed3a5b26..b29cd344f 100644
--- a/tests/lang.sh
+++ b/tests/lang.sh
@@ -27,7 +27,7 @@ done
 for i in lang/eval-fail-*.nix; do
     echo "evaluating $i (should fail)";
     i=$(basename $i .nix)
-    if $nixinstantiate --eval-only - < lang/$i.nix; then
+    if $nixinstantiate --eval-only lang/$i.nix; then
         echo "FAIL: $i shouldn't evaluate"
         fail=1
     fi
@@ -38,7 +38,7 @@ for i in lang/eval-okay-*.nix; do
     i=$(basename $i .nix)
 
     if test -e lang/$i.exp; then
-        if ! $nixinstantiate --eval-only - < lang/$i.nix > lang/$i.out; then
+        if ! $nixinstantiate --eval-only lang/$i.nix > lang/$i.out; then
             echo "FAIL: $i should evaluate"
             fail=1
         fi
@@ -49,7 +49,7 @@ for i in lang/eval-okay-*.nix; do
     fi
     
     if test -e lang/$i.exp.xml; then
-        if ! $nixinstantiate --eval-only --xml --strict - < lang/$i.nix > lang/$i.out.xml; then
+        if ! $nixinstantiate --eval-only --xml --strict lang/$i.nix > lang/$i.out.xml; then
             echo "FAIL: $i should evaluate"
             fail=1
         fi
diff --git a/tests/lang/eval-okay-arithmetic.exp b/tests/lang/eval-okay-arithmetic.exp
new file mode 100644
index 000000000..433cb1c9b
--- /dev/null
+++ b/tests/lang/eval-okay-arithmetic.exp
@@ -0,0 +1 @@
+Int(1275)
diff --git a/tests/lang/eval-okay-arithmetic.nix b/tests/lang/eval-okay-arithmetic.nix
new file mode 100644
index 000000000..735f01cf4
--- /dev/null
+++ b/tests/lang/eval-okay-arithmetic.nix
@@ -0,0 +1,18 @@
+with import ./lib.nix;
+
+let {
+
+  range = first: last: [first] ++ (if first == last then [] else range (builtins.add first 1) last);
+
+  /* Supposedly tail recursive version:
+  
+  range_ = accum: first: last: 
+    if first == last then ([first] ++ accum)
+    else range_ ([first] ++ accum) (builtins.add first 1) last;
+
+  range = range_ [];
+  */
+
+  body = sum (range 1 50);
+
+}
diff --git a/tests/lang/eval-okay-flatten.nix b/tests/lang/eval-okay-flatten.nix
index 2019263b8..fe911e968 100644
--- a/tests/lang/eval-okay-flatten.nix
+++ b/tests/lang/eval-okay-flatten.nix
@@ -1,17 +1,6 @@
-let {
-
-  fold = op: nul: list:
-    if list == []
-    then nul
-    else op (builtins.head list) (fold op nul (builtins.tail list));
+with import ./lib.nix;
 
-  concat =
-    fold (x: y: x + y) "";
-    
-  flatten = x:
-    if builtins.isList x
-    then fold (x: y: (flatten x) ++ y) [] x
-    else [x];
+let {
 
   l = ["1" "2" ["3" ["4"] ["5" "6"]] "7"];
 
diff --git a/tests/lang/eval-okay-list.nix b/tests/lang/eval-okay-list.nix
index 72a120d0d..d433bcf90 100644
--- a/tests/lang/eval-okay-list.nix
+++ b/tests/lang/eval-okay-list.nix
@@ -1,12 +1,6 @@
-let {
-
-  fold = op: nul: list:
-    if list == []
-    then nul
-    else op (builtins.head list) (fold op nul (builtins.tail list));
+with import ./lib.nix;
 
-  concat =
-    fold (x: y: x + y) "";
+let {
 
   body = concat ["foo" "bar" "bla" "test"];
     
diff --git a/tests/lang/eval-okay-map.exp b/tests/lang/eval-okay-map.exp
index ab8e7a278..703cb0a30 100644
--- a/tests/lang/eval-okay-map.exp
+++ b/tests/lang/eval-okay-map.exp
@@ -1 +1 @@
-List([Call(Function1("x",OpPlus(Var("x"),Str("bar")),Pos("(string)",1,7)),Str("foo")),Call(Function1("x",OpPlus(Var("x"),Str("bar")),Pos("(string)",1,7)),Str("bla")),Call(Function1("x",OpPlus(Var("x"),Str("bar")),Pos("(string)",1,7)),Str("xyzzy"))])
+Str("foobarblabarxyzzybar")
diff --git a/tests/lang/eval-okay-map.nix b/tests/lang/eval-okay-map.nix
index 924446657..a76c1d811 100644
--- a/tests/lang/eval-okay-map.nix
+++ b/tests/lang/eval-okay-map.nix
@@ -1 +1,3 @@
-map (x: x + "bar") [ "foo" "bla" "xyzzy" ]
-\ No newline at end of file
+with import ./lib.nix;
+
+concat (map (x: x + "bar") [ "foo" "bla" "xyzzy" ])
+\ No newline at end of file
diff --git a/tests/lang/lib.nix b/tests/lang/lib.nix
new file mode 100644
index 000000000..f888453ff
--- /dev/null
+++ b/tests/lang/lib.nix
@@ -0,0 +1,18 @@
+rec {
+
+  fold = op: nul: list:
+    if list == []
+    then nul
+    else op (builtins.head list) (fold op nul (builtins.tail list));
+
+  concat =
+    fold (x: y: x + y) "";
+
+  flatten = x:
+    if builtins.isList x
+    then fold (x: y: (flatten x) ++ y) [] x
+    else [x];
+
+  sum = fold (x: y: builtins.add x y) 0;
+
+}