* Refactoring: put the Nix expression evaluator in its own library so

  that it can be used by multiple programs.

1 files changed, 215 insertions, 0 deletions

diff --git a/src/libexpr/nixexpr.cc b/src/libexpr/nixexpr.cc
new file mode 100644
index 000000000..816b39dc1
--- /dev/null
+++ b/src/libexpr/nixexpr.cc
@@ -0,0 +1,215 @@
+#include "nixexpr.hh"
+#include "storeexpr.hh"
+
+
+ATermMap::ATermMap(unsigned int initialSize, unsigned int maxLoadPct)
+{
+    table = ATtableCreate(initialSize, maxLoadPct);
+    if (!table) throw Error("cannot create ATerm table");
+}
+
+
+ATermMap::ATermMap(const ATermMap & map)
+    : table(0)
+{
+    ATermList keys = map.keys();
+
+    /* !!! adjust allocation for load pct */
+    table = ATtableCreate(ATgetLength(keys), map.maxLoadPct);
+    if (!table) throw Error("cannot create ATerm table");
+
+    for (ATermIterator i(keys); i; ++i)
+        set(*i, map.get(*i));
+}
+
+
+ATermMap::~ATermMap()
+{
+    if (table) ATtableDestroy(table);
+}
+
+
+void ATermMap::set(ATerm key, ATerm value)
+{
+    return ATtablePut(table, key, value);
+}
+
+
+void ATermMap::set(const string & key, ATerm value)
+{
+    set(string2ATerm(key), value);
+}
+
+
+ATerm ATermMap::get(ATerm key) const
+{
+    return ATtableGet(table, key);
+}
+
+
+ATerm ATermMap::get(const string & key) const
+{
+    return get(string2ATerm(key));
+}
+
+
+void ATermMap::remove(ATerm key)
+{
+    ATtableRemove(table, key);
+}
+
+
+void ATermMap::remove(const string & key)
+{
+    remove(string2ATerm(key));
+}
+
+
+ATermList ATermMap::keys() const
+{
+    ATermList keys = ATtableKeys(table);
+    if (!keys) throw Error("cannot query aterm map keys");
+    return keys;
+}
+
+
+ATerm string2ATerm(const string & s)
+{
+    return (ATerm) ATmakeAppl0(ATmakeAFun((char *) s.c_str(), 0, ATtrue));
+}
+
+
+string aterm2String(ATerm t)
+{
+    return ATgetName(ATgetAFun(t));
+}
+    
+
+ATerm bottomupRewrite(TermFun & f, ATerm e)
+{
+    if (ATgetType(e) == AT_APPL) {
+        AFun fun = ATgetAFun(e);
+        int arity = ATgetArity(fun);
+        ATermList args = ATempty;
+
+        for (int i = arity - 1; i >= 0; i--)
+            args = ATinsert(args, bottomupRewrite(f, ATgetArgument(e, i)));
+        
+        e = (ATerm) ATmakeApplList(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);
+    }
+
+    return f(e);
+}
+
+
+void queryAllAttrs(Expr e, ATermMap & attrs)
+{
+    ATMatcher m;
+    ATermList bnds;
+    if (!(atMatch(m, e) >> "Attrs" >> bnds))
+        throw badTerm("expected attribute set", e);
+
+    for (ATermIterator i(bnds); i; ++i) {
+        string s;
+        Expr e;
+        if (!(atMatch(m, *i) >> "Bind" >> s >> e))
+            abort(); /* can't happen */
+        attrs.set(s, e);
+    }
+}
+
+
+Expr queryAttr(Expr e, const string & name)
+{
+    ATermMap attrs;
+    queryAllAttrs(e, attrs);
+    return attrs.get(name);
+}
+
+
+Expr makeAttrs(const ATermMap & attrs)
+{
+    ATermList bnds = ATempty;
+    for (ATermIterator i(attrs.keys()); i; ++i)
+        bnds = ATinsert(bnds, 
+            ATmake("Bind(<term>, <term>)", *i, attrs.get(*i)));
+    return ATmake("Attrs(<term>)", ATreverse(bnds));
+}
+
+
+Expr substitute(const ATermMap & subs, Expr e)
+{
+    ATMatcher m;
+    string s;
+
+    if (atMatch(m, e) >> "Var" >> s) {
+        Expr sub = subs.get(s);
+        return sub ? sub : e;
+    }
+
+    /* In case of a function, filter out all variables bound by this
+       function. */
+    ATermList formals;
+    ATerm body;
+    if (atMatch(m, e) >> "Function" >> formals >> body) {
+        ATermMap subs2(subs);
+        for (ATermIterator i(formals); i; ++i) {
+            Expr def;
+            if (!(atMatch(m, *i) >> "NoDefFormal" >> s) &&
+                !(atMatch(m, *i) >> "DefFormal" >> s >> def))
+                abort();
+            subs2.remove(s);
+        }
+        return ATmake("Function(<term>, <term>)", formals,
+            substitute(subs2, body));
+    }
+
+    /* Idem for a mutually recursive attribute set. */
+    ATermList bindings;
+    if (atMatch(m, e) >> "Rec" >> bindings) {
+        ATermMap subs2(subs);
+        for (ATermIterator i(bindings); i; ++i) {
+            Expr e;
+            if (!(atMatch(m, *i) >> "Bind" >> s >> e))
+                abort(); /* can't happen */
+            subs2.remove(s);
+        }
+        return ATmake("Rec(<term>)", substitute(subs2, (ATerm) bindings));
+    }
+
+    if (ATgetType(e) == AT_APPL) {
+        AFun fun = ATgetAFun(e);
+        int arity = ATgetArity(fun);
+        ATermList args = ATempty;
+
+        for (int i = arity - 1; i >= 0; i--)
+            args = ATinsert(args, substitute(subs, ATgetArgument(e, i)));
+        
+        return (ATerm) ATmakeApplList(fun, args);
+    }
+
+    if (ATgetType(e) == AT_LIST) {
+        ATermList out = ATempty;
+        for (ATermIterator i((ATermList) e); i; ++i)
+            out = ATinsert(out, substitute(subs, *i));
+        return (ATerm) ATreverse(out);
+    }
+
+    return e;
+}
+
+
+Expr makeBool(bool b)
+{
+    return b ? ATmake("Bool(True)") : ATmake("Bool(False)");
+}