* Started integrating the new evaluator.

7 files changed, 736 insertions, 708 deletions

diff --git a/src/libexpr/attr-path.cc b/src/libexpr/attr-path.cc
index e8e4c050cc..5d81303fe3 100644
--- a/src/libexpr/attr-path.cc
+++ b/src/libexpr/attr-path.cc
@@ -6,6 +6,7 @@
 namespace nix {
 
 
+#if 0
 bool isAttrs(EvalState & state, Expr e, ATermMap & attrs)
 {
     e = evalExpr(state, e);
@@ -77,6 +78,7 @@ Expr findAlongAttrPath(EvalState & state, const string & attrPath,
     
     return e;
 }
+#endif
 
  
 }
diff --git a/src/libexpr/eval-test.cc b/src/libexpr/eval-test.cc
index 543a9cf852..d37014a731 100644
--- a/src/libexpr/eval-test.cc
+++ b/src/libexpr/eval-test.cc
@@ -10,668 +10,13 @@
 using namespace nix;
 
 
-struct Env;
-struct Value;
-
-typedef ATerm Sym;
-
-typedef std::map<Sym, Value> Bindings;
-
-
-struct Env
-{
-    Env * up;
-    Bindings bindings;
-};
-
-
-typedef enum {
-    tInt = 1,
-    tBool,
-    tString,
-    tPath,
-    tNull,
-    tAttrs,
-    tList,
-    tThunk,
-    tLambda,
-    tCopy,
-    tBlackhole,
-    tPrimOp,
-    tPrimOpApp,
-} ValueType;
-
-
-typedef void (* PrimOp_) (Value * * args, Value & v);
-
-
-struct Value
-{
-    ValueType type;
-    union 
-    {
-        int integer;
-        bool boolean;
-        struct {
-            const char * s;
-            const char * * context;
-        } string;
-        Bindings * attrs;
-        struct {
-            unsigned int length;
-            Value * elems;
-        } list;
-        struct {
-            Env * env;
-            Expr expr;
-        } thunk;
-        struct {
-            Env * env;
-            Pattern pat;
-            Expr body;
-        } lambda;
-        Value * val;
-        struct {
-            PrimOp_ fun;
-            unsigned int arity;
-        } primOp;
-        struct {
-            Value * left, * right;
-            unsigned int argsLeft;
-        } primOpApp;
-    };
-};
-
-
-static void mkThunk(Value & v, Env & env, Expr expr)
-{
-    v.type = tThunk;
-    v.thunk.env = &env;
-    v.thunk.expr = expr;
-}
-
-
-static void mkInt(Value & v, int n)
-{
-    v.type = tInt;
-    v.integer = n;
-}
-
-
-static void mkBool(Value & v, bool b)
-{
-    v.type = tBool;
-    v.boolean = b;
-}
-
-
-static void mkString(Value & v, const char * s)
-{
-    v.type = tString;
-    v.string.s = s;
-    v.string.context = 0;
-}
-
-
-std::ostream & operator << (std::ostream & str, Value & v)
-{
-    switch (v.type) {
-    case tInt:
-        str << v.integer;
-        break;
-    case tBool:
-        str << (v.boolean ? "true" : "false");
-        break;
-    case tString:
-        str << "\"" << v.string.s << "\""; // !!! escaping
-        break;
-    case tNull:
-        str << "true";
-        break;
-    case tAttrs:
-        str << "{ ";
-        foreach (Bindings::iterator, i, *v.attrs)
-            str << aterm2String(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:
-        str << "<CODE>";
-        break;
-    case tLambda:
-        str << "<LAMBDA>";
-        break;
-    case tPrimOp:
-        str << "<PRIMOP>";
-        break;
-    case tPrimOpApp:
-        str << "<PRIMOP-APP>";
-        break;
-    default:
-        abort();
-    }
-    return str;
-}
-
-
-static void eval(Env & env, Expr e, Value & v);
-
-
-string showType(Value & v)
-{
-    switch (v.type) {
-        case tString: return "a string";
-        case tPath: return "a path";
-        case tNull: return "null";
-        case tInt: return "an integer";
-        case tBool: return "a boolean";
-        case tLambda: return "a function";
-        case tAttrs: return "an attribute set";
-        case tList: return "a list";
-        case tPrimOpApp: return "a partially applied built-in function";
-        default: throw Error("unknown type");
-    }
-}
-
-
-static void forceValue(Value & v)
-{
-    if (v.type == tThunk) {
-        v.type = tBlackhole;
-        eval(*v.thunk.env, v.thunk.expr, v);
-    }
-    else if (v.type == tCopy) {
-        forceValue(*v.val);
-        v = *v.val;
-    }
-    else if (v.type == tBlackhole)
-        throw EvalError("infinite recursion encountered");
-}
-
-
-static void forceInt(Value & v)
-{
-    forceValue(v);
-    if (v.type != tInt)
-        throw TypeError(format("value is %1% while an integer was expected") % showType(v));
-}
-
-
-static void forceAttrs(Value & v)
-{
-    forceValue(v);
-    if (v.type != tAttrs)
-        throw TypeError(format("value is %1% while an attribute set was expected") % showType(v));
-}
-
-
-static void forceList(Value & v)
-{
-    forceValue(v);
-    if (v.type != tList)
-        throw TypeError(format("value is %1% while a list was expected") % showType(v));
-}
-
-
-static Value * lookupWith(Env * env, Sym name)
-{
-    if (!env) return 0;
-    Value * v = lookupWith(env->up, name);
-    if (v) return v;
-    Bindings::iterator i = env->bindings.find(sWith);
-    if (i == env->bindings.end()) return 0;
-    Bindings::iterator j = i->second.attrs->find(name);
-    if (j != i->second.attrs->end()) return &j->second;
-    return 0;
-}
-
-
-static Value * lookupVar(Env * env, Sym name)
-{
-    /* First look for a regular variable binding for `name'. */
-    for (Env * env2 = env; env2; env2 = env2->up) {
-        Bindings::iterator i = env2->bindings.find(name);
-        if (i != env2->bindings.end()) return &i->second;
-    }
-
-    /* Otherwise, look for a `with' attribute set containing `name'.
-       Outer `withs' take precedence (i.e. `with {x=1;}; with {x=2;};
-       x' evaluates to 1).  */
-    Value * v = lookupWith(env, name);
-    if (v) return v;
-
-    /* Alternative implementation where the inner `withs' take
-       precedence (i.e. `with {x=1;}; with {x=2;}; x' evaluates to
-       2). */
-#if 0
-    for (Env * env2 = env; env2; env2 = env2->up) {
-        Bindings::iterator i = env2->bindings.find(sWith);
-        if (i == env2->bindings.end()) continue;
-        Bindings::iterator j = i->second.attrs->find(name);
-        if (j != i->second.attrs->end()) return &j->second;
-    }
-#endif
-    
-    throw Error("undefined variable");
-}
-
-
-static bool eqValues(Value & v1, Value & v2)
-{
-    forceValue(v1);
-    forceValue(v2);
-    switch (v1.type) {
-
-        case tInt:
-            return v2.type == tInt && v1.integer == v2.integer;
-
-        case tBool:
-            return v2.type == tBool && v1.boolean == v2.boolean;
-
-        case tList:
-            if (v2.type != tList || 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 (v2.type != tAttrs || 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 (!eqValues(i->second, j->second)) return false;
-            return true;
-        }
-
-        default:
-            throw Error("cannot compare given values");
-    }
-}
-
-
-unsigned long nrValues = 0, nrEnvs = 0, nrEvaluated = 0;
-
-static Value * allocValues(unsigned int count)
-{
-    nrValues += count;
-    return new Value[count]; // !!! check destructor
-}
-
-static Env & allocEnv()
-{
-    nrEnvs++;
-    return *(new Env);
-}
-
-
-char * p1 = 0, * p2 = 0;
-
-
-static bool evalBool(Env & env, Expr e)
-{
-    Value v;
-    eval(env, e, v);
-    if (v.type != tBool)
-        throw TypeError(format("value is %1% while a Boolean was expected") % showType(v));
-    return v.boolean;
-}
-
-
-static void eval(Env & env, Expr e, Value & v)
-{
-    char c;
-    if (!p1) p1 = &c; else if (!p2) p2 = &c;
-
-    printMsg(lvlError, format("eval: %1%") % e);
-
-    nrEvaluated++;
-
-    Sym name;
-    if (matchVar(e, name)) {
-        Value * v2 = lookupVar(&env, name);
-        forceValue(*v2);
-        v = *v2;
-        return;
-    }
-
-    int n;
-    if (matchInt(e, n)) {
-        mkInt(v, n);
-        return;
-    }
-
-    ATerm s; ATermList context;
-    if (matchStr(e, s, context)) {
-        assert(context == ATempty);
-        mkString(v, ATgetName(ATgetAFun(s)));
-        return;
-    }
-
-    ATermList es;
-    if (matchAttrs(e, es)) {
-        v.type = tAttrs;
-        v.attrs = new Bindings;
-        ATerm e2, pos;
-        for (ATermIterator i(es); i; ++i) {
-            if (!matchBind(*i, name, e2, pos)) abort(); /* can't happen */
-            Value & v2 = (*v.attrs)[name];
-            nrValues++;
-            mkThunk(v2, env, e2);
-        }
-        return;
-    }
-
-    ATermList rbnds, nrbnds;
-    if (matchRec(e, rbnds, nrbnds)) {
-        Env & env2(allocEnv());
-        env2.up = &env;
-        
-        v.type = tAttrs;
-        v.attrs = &env2.bindings;
-        ATerm name, e2, pos;
-        for (ATermIterator i(rbnds); i; ++i) {
-            if (!matchBind(*i, name, e2, pos)) abort(); /* can't happen */
-            Value & v2 = env2.bindings[name];
-            nrValues++;
-            mkThunk(v2, env2, e2);
-        }
-        
-        return;
-    }
-
-    Expr e1, e2;
-    if (matchSelect(e, e2, name)) {
-        eval(env, e2, v);
-        forceAttrs(v); // !!! eval followed by force is slightly inefficient
-        Bindings::iterator i = v.attrs->find(name);
-        if (i == v.attrs->end()) throw TypeError("attribute not found");
-        forceValue(i->second);
-        v = i->second;
-        return;
-    }
-
-    Pattern pat; Expr body; Pos pos;
-    if (matchFunction(e, pat, body, pos)) {
-        v.type = tLambda;
-        v.lambda.env = &env;
-        v.lambda.pat = pat;
-        v.lambda.body = body;
-        return;
-    }
-
-    Expr fun, arg;
-    if (matchCall(e, fun, arg)) {
-        eval(env, fun, v);
-
-        if (v.type == tPrimOp || v.type == tPrimOpApp) {
-            unsigned int argsLeft =
-                v.type == tPrimOp ? v.primOp.arity : v.primOpApp.argsLeft;
-            if (argsLeft == 1) {
-                /* We have all the arguments, so call the primop.
-                   First find the primop. */
-                Value * primOp = &v;
-                while (primOp->type == tPrimOpApp) primOp = primOp->primOpApp.left;
-                assert(primOp->type == tPrimOp);
-                unsigned int arity = primOp->primOp.arity;
-                
-                Value vLastArg;
-                mkThunk(vLastArg, env, arg);
-
-                /* Put all the arguments in an array. */
-                Value * vArgs[arity];
-                unsigned int n = arity - 1;
-                vArgs[n--] = &vLastArg;
-                for (Value * arg = &v; arg->type == tPrimOpApp; arg = arg->primOpApp.left)
-                    vArgs[n--] = arg->primOpApp.right;
-
-                /* And call the primop. */
-                primOp->primOp.fun(vArgs, v);
-            } else {
-                Value * v2 = allocValues(2);
-                v2[0] = v;
-                mkThunk(v2[1], env, arg);
-                v.type = tPrimOpApp;
-                v.primOpApp.left = &v2[0];
-                v.primOpApp.right = &v2[1];
-                v.primOpApp.argsLeft = argsLeft - 1;
-            }
-            return;
-        }
-        
-        if (v.type != tLambda) throw TypeError("expected function");
-
-        Env & env2(allocEnv());
-        env2.up = &env;
-
-        ATermList formals; ATerm ellipsis;
-
-        if (matchVarPat(v.lambda.pat, name)) {
-            Value & vArg = env2.bindings[name];
-            nrValues++;
-            mkThunk(vArg, env, arg);
-        }
-
-        else if (matchAttrsPat(v.lambda.pat, formals, ellipsis, name)) {
-            Value * vArg;
-            Value vArg_;
-
-            if (name == sNoAlias)
-                vArg = &vArg_;
-            else {
-                vArg = &env2.bindings[name];
-                nrValues++;
-            }                
-
-            eval(env, arg, *vArg);
-            forceAttrs(*vArg);
-            
-            /* 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 def; Sym name;
-                DefaultValue def2;
-                if (!matchFormal(*i, name, def2)) abort(); /* can't happen */
-
-                Bindings::iterator j = vArg->attrs->find(name);
-                
-                Value & v = env2.bindings[name];
-                nrValues++;
-                
-                if (j == vArg->attrs->end()) {
-                    if (!matchDefaultValue(def2, def)) def = 0;
-                    if (def == 0) throw TypeError(format("the argument named `%1%' required by the function is missing")
-                        % aterm2String(name));
-                    mkThunk(v, env2, def);
-                } else {
-                    attrsUsed++;
-                    v.type = tCopy;
-                    v.val = &j->second;
-                }
-            }
-
-            /* 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 (ellipsis == eFalse && attrsUsed != vArg->attrs->size())
-                throw TypeError("function called with unexpected argument");
-        }
-
-        else abort();
-        
-        eval(env2, v.lambda.body, v);
-        return;
-    }
-
-    Expr attrs;
-    if (matchWith(e, attrs, body, pos)) {
-        Env & env2(allocEnv());
-        env2.up = &env;
-
-        Value & vAttrs = env2.bindings[sWith];
-        nrValues++;
-        eval(env, attrs, vAttrs);
-        forceAttrs(vAttrs);
-        
-        eval(env2, body, v);
-        return;
-    }
-
-    if (matchList(e, es)) {
-        v.type = tList;
-        v.list.length = ATgetLength(es);
-        v.list.elems = allocValues(v.list.length);
-        for (unsigned int n = 0; n < v.list.length; ++n, es = ATgetNext(es))
-            mkThunk(v.list.elems[n], env, ATgetFirst(es));
-        return;
-    }
-
-    if (matchOpEq(e, e1, e2)) {
-        Value v1; eval(env, e1, v1);
-        Value v2; eval(env, e2, v2);
-        mkBool(v, eqValues(v1, v2));
-        return;
-    }
-
-    if (matchOpNEq(e, e1, e2)) {
-        Value v1; eval(env, e1, v1);
-        Value v2; eval(env, e2, v2);
-        mkBool(v, !eqValues(v1, v2));
-        return;
-    }
-
-    if (matchOpConcat(e, e1, e2)) {
-        Value v1; eval(env, e1, v1);
-        forceList(v1);
-        Value v2; eval(env, e2, v2);
-        forceList(v2);
-        v.type = tList;
-        v.list.length = v1.list.length + v2.list.length;
-        v.list.elems = allocValues(v.list.length);
-        /* !!! This loses sharing with the original lists.  We could
-           use a tCopy node, but that would use more memory. */
-        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];
-        return;
-    }
-
-    if (matchConcatStrings(e, es)) {
-        unsigned int n = ATgetLength(es), j = 0;
-        Value vs[n];
-        unsigned int len = 0;
-        for (ATermIterator i(es); i; ++i, ++j) {
-            eval(env, *i, vs[j]);
-            if (vs[j].type != tString) throw TypeError("string expected");
-            len += strlen(vs[j].string.s);
-        }
-        char * s = new char[len + 1], * t = s;
-        for (unsigned int i = 0; i < j; ++i) {
-            strcpy(t, vs[i].string.s);
-            t += strlen(vs[i].string.s);
-        }
-        *t = 0;
-        mkString(v, s);
-        return;
-    }
-
-    Expr e3;
-    if (matchIf(e, e1, e2, e3)) {
-        eval(env, evalBool(env, e1) ? e2 : e3, v);
-        return;
-    }
-
-    if (matchOpOr(e, e1, e2)) {
-        mkBool(v, evalBool(env, e1) || evalBool(env, e2));
-        return;
-    }
-
-    throw Error("unsupported term");
-}
-
-
-static void strictEval(Env & env, Expr e, Value & v)
-{
-    eval(env, e, v);
-    
-    if (v.type == tAttrs) {
-        foreach (Bindings::iterator, i, *v.attrs)
-            forceValue(i->second);
-    }
-    
-    else if (v.type == tList) {
-        for (unsigned int n = 0; n < v.list.length; ++n)
-            forceValue(v.list.elems[n]);
-    }
-}
-
-
-static void prim_head(Value * * args, Value & v)
-{
-    forceList(*args[0]);
-    if (args[0]->list.length == 0)
-        throw Error("`head' called on an empty list");
-    forceValue(args[0]->list.elems[0]);
-    v = args[0]->list.elems[0];
-}
-
-
-static void prim_add(Value * * args, Value & v)
-{
-    forceInt(*args[0]);
-    forceInt(*args[1]);
-    mkInt(v, args[0]->integer + args[1]->integer);
-}
-
-
-static void addPrimOp(Env & env, const string & name, unsigned int arity, PrimOp_ fun)
-{
-    Value & v = env.bindings[toATerm(name)];
-    nrValues++;
-    v.type = tPrimOp;
-    v.primOp.arity = arity;
-    v.primOp.fun = fun;
-}
-
-
 void doTest(string s)
 {
-    Env baseEnv;
-    baseEnv.up = 0;
-
-    /* Add global constants such as `true' to the base environment. */
-    {
-        Value & v = baseEnv.bindings[toATerm("true")];
-        v.type = tBool;
-        v.boolean = true;
-    }
-    {
-        Value & v = baseEnv.bindings[toATerm("false")];
-        v.type = tBool;
-        v.boolean = false;
-    }
-    {
-        Value & v = baseEnv.bindings[toATerm("null")];
-        v.type = tNull;
-    }
-
-    /* Add primops to the base environment. */
-    addPrimOp(baseEnv, "__head", 1, prim_head);
-    addPrimOp(baseEnv, "__add", 2, prim_add);
-    
-    p1 = p2 = 0;
     EvalState state;
     Expr e = parseExprFromString(state, s, "/");
     printMsg(lvlError, format(">>>>> %1%") % e);
     Value v;
-    strictEval(baseEnv, e, v);
+    state.strictEval(e, v);
     printMsg(lvlError, format("result: %1%") % v);
 }
 
@@ -721,11 +66,6 @@ void run(Strings args)
     doTest("if false then 1 else 2");
     doTest("if false || true then 1 else 2");
     doTest("let x = x; in if true || x then 1 else 2");
-    
-    printMsg(lvlError, format("alloced %1% values") % nrValues);
-    printMsg(lvlError, format("alloced %1% environments") % nrEnvs);
-    printMsg(lvlError, format("evaluated %1% expressions") % nrEvaluated);
-    printMsg(lvlError, format("each eval() uses %1% bytes of stack space") % (p1 - p2));
 }
 
 
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 1501fc0480..794e396602 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -7,6 +7,8 @@
 #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
@@ -15,15 +17,77 @@
 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 << "\"" << v.string.s << "\""; // !!! escaping
+        break;
+    case tNull:
+        str << "true";
+        break;
+    case tAttrs:
+        str << "{ ";
+        foreach (Bindings::iterator, i, *v.attrs)
+            str << aterm2String(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:
+        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(Value & v)
+{
+    switch (v.type) {
+        case tString: return "a string";
+        case tPath: return "a path";
+        case tNull: return "null";
+        case tInt: return "an integer";
+        case tBool: return "a boolean";
+        case tLambda: return "a function";
+        case tAttrs: return "an attribute set";
+        case tList: return "a list";
+        case tPrimOpApp: return "a partially applied built-in function";
+        default: throw Error("unknown type");
+    }
+}
+
 
+EvalState::EvalState() : baseEnv(allocEnv())
+{
+    nrValues = nrEnvs = nrEvaluated = 0;
+
+    initNixExprHelpers();
+
+    createBaseEnv();
+    
     allowUnsafeEquality = getEnv("NIX_NO_UNSAFE_EQ", "") == "";
 }
 
@@ -31,7 +95,11 @@ EvalState::EvalState()
 void EvalState::addPrimOp(const string & name,
     unsigned int arity, PrimOp primOp)
 {
-    primOps.set(toATerm(name), makePrimOpDef(arity, ATmakeBlob(0, (void *) primOp)));
+    Value & v = baseEnv.bindings[toATerm(name)];
+    nrValues++;
+    v.type = tPrimOp;
+    v.primOp.arity = arity;
+    v.primOp.fun = primOp;
 }
 
 
@@ -76,6 +144,471 @@ LocalNoInline(void addErrorPrefix(Error & e, const char * s, const string & s2,
 }
 
 
+static void mkThunk(Value & v, Env & env, Expr expr)
+{
+    v.type = tThunk;
+    v.thunk.env = &env;
+    v.thunk.expr = expr;
+}
+
+
+static Value * lookupWith(Env * env, Sym name)
+{
+    if (!env) return 0;
+    Value * v = lookupWith(env->up, name);
+    if (v) return v;
+    Bindings::iterator i = env->bindings.find(sWith);
+    if (i == env->bindings.end()) return 0;
+    Bindings::iterator j = i->second.attrs->find(name);
+    if (j != i->second.attrs->end()) return &j->second;
+    return 0;
+}
+
+
+static Value * lookupVar(Env * env, Sym name)
+{
+    /* First look for a regular variable binding for `name'. */
+    for (Env * env2 = env; env2; env2 = env2->up) {
+        Bindings::iterator i = env2->bindings.find(name);
+        if (i != env2->bindings.end()) return &i->second;
+    }
+
+    /* Otherwise, look for a `with' attribute set containing `name'.
+       Outer `withs' take precedence (i.e. `with {x=1;}; with {x=2;};
+       x' evaluates to 1).  */
+    Value * v = lookupWith(env, name);
+    if (v) return v;
+
+    /* Alternative implementation where the inner `withs' take
+       precedence (i.e. `with {x=1;}; with {x=2;}; x' evaluates to
+       2). */
+#if 0
+    for (Env * env2 = env; env2; env2 = env2->up) {
+        Bindings::iterator i = env2->bindings.find(sWith);
+        if (i == env2->bindings.end()) continue;
+        Bindings::iterator j = i->second.attrs->find(name);
+        if (j != i->second.attrs->end()) return &j->second;
+    }
+#endif
+    
+    throw Error("undefined variable");
+}
+
+
+Value * EvalState::allocValues(unsigned int count)
+{
+    nrValues += count;
+    return new Value[count]; // !!! check destructor
+}
+
+
+Env & EvalState::allocEnv()
+{
+    nrEnvs++;
+    return *(new Env);
+}
+
+
+static char * deepestStack = (char *) -1; /* for measuring stack usage */
+
+
+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! */
+    
+    char x;
+    if (&x < deepestStack) deepestStack = &x;
+    
+    printMsg(lvlError, format("eval: %1%") % e);
+
+    nrEvaluated++;
+
+    Sym name;
+    if (matchVar(e, name)) {
+        Value * v2 = lookupVar(&env, name);
+        forceValue(*v2);
+        v = *v2;
+        return;
+    }
+
+    int n;
+    if (matchInt(e, n)) {
+        mkInt(v, n);
+        return;
+    }
+
+    ATerm s; ATermList context;
+    if (matchStr(e, s, context)) {
+        assert(context == ATempty);
+        mkString(v, ATgetName(ATgetAFun(s)));
+        return;
+    }
+
+    ATermList es;
+    if (matchAttrs(e, es)) {
+        v.type = tAttrs;
+        v.attrs = new Bindings;
+        ATerm e2, pos;
+        for (ATermIterator i(es); i; ++i) {
+            if (!matchBind(*i, name, e2, pos)) abort(); /* can't happen */
+            Value & v2 = (*v.attrs)[name];
+            nrValues++;
+            mkThunk(v2, env, e2);
+        }
+        return;
+    }
+
+    ATermList rbnds, nrbnds;
+    if (matchRec(e, rbnds, nrbnds)) {
+        Env & env2(allocEnv());
+        env2.up = &env;
+        
+        v.type = tAttrs;
+        v.attrs = &env2.bindings;
+        ATerm name, e2, pos;
+        for (ATermIterator i(rbnds); i; ++i) {
+            if (!matchBind(*i, name, e2, pos)) abort(); /* can't happen */
+            Value & v2 = env2.bindings[name];
+            nrValues++;
+            mkThunk(v2, env2, e2);
+        }
+        
+        return;
+    }
+
+    Expr e1, e2;
+    if (matchSelect(e, e2, name)) {
+        eval(env, e2, v);
+        forceAttrs(v); // !!! eval followed by force is slightly inefficient
+        Bindings::iterator i = v.attrs->find(name);
+        if (i == v.attrs->end()) throw TypeError("attribute not found");
+        forceValue(i->second);
+        v = i->second;
+        return;
+    }
+
+    Pattern pat; Expr body; Pos pos;
+    if (matchFunction(e, pat, body, pos)) {
+        v.type = tLambda;
+        v.lambda.env = &env;
+        v.lambda.pat = pat;
+        v.lambda.body = body;
+        return;
+    }
+
+    Expr fun, arg;
+    if (matchCall(e, fun, arg)) {
+        eval(env, fun, v);
+
+        if (v.type == tPrimOp || v.type == tPrimOpApp) {
+            unsigned int argsLeft =
+                v.type == tPrimOp ? v.primOp.arity : v.primOpApp.argsLeft;
+            if (argsLeft == 1) {
+                /* We have all the arguments, so call the primop.
+                   First find the primop. */
+                Value * primOp = &v;
+                while (primOp->type == tPrimOpApp) primOp = primOp->primOpApp.left;
+                assert(primOp->type == tPrimOp);
+                unsigned int arity = primOp->primOp.arity;
+                
+                Value vLastArg;
+                mkThunk(vLastArg, env, arg);
+
+                /* Put all the arguments in an array. */
+                Value * vArgs[arity];
+                unsigned int n = arity - 1;
+                vArgs[n--] = &vLastArg;
+                for (Value * arg = &v; arg->type == tPrimOpApp; arg = arg->primOpApp.left)
+                    vArgs[n--] = arg->primOpApp.right;
+
+                /* And call the primop. */
+                primOp->primOp.fun(*this, vArgs, v);
+            } else {
+                Value * v2 = allocValues(2);
+                v2[0] = v;
+                mkThunk(v2[1], env, arg);
+                v.type = tPrimOpApp;
+                v.primOpApp.left = &v2[0];
+                v.primOpApp.right = &v2[1];
+                v.primOpApp.argsLeft = argsLeft - 1;
+            }
+            return;
+        }
+        
+        if (v.type != tLambda) throw TypeError("expected function");
+
+        Env & env2(allocEnv());
+        env2.up = &env;
+
+        ATermList formals; ATerm ellipsis;
+
+        if (matchVarPat(v.lambda.pat, name)) {
+            Value & vArg = env2.bindings[name];
+            nrValues++;
+            mkThunk(vArg, env, arg);
+        }
+
+        else if (matchAttrsPat(v.lambda.pat, formals, ellipsis, name)) {
+            Value * vArg;
+            Value vArg_;
+
+            if (name == sNoAlias)
+                vArg = &vArg_;
+            else {
+                vArg = &env2.bindings[name];
+                nrValues++;
+            }                
+
+            eval(env, arg, *vArg);
+            forceAttrs(*vArg);
+            
+            /* 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 def; Sym name;
+                DefaultValue def2;
+                if (!matchFormal(*i, name, def2)) abort(); /* can't happen */
+
+                Bindings::iterator j = vArg->attrs->find(name);
+                
+                Value & v = env2.bindings[name];
+                nrValues++;
+                
+                if (j == vArg->attrs->end()) {
+                    if (!matchDefaultValue(def2, def)) def = 0;
+                    if (def == 0) throw TypeError(format("the argument named `%1%' required by the function is missing")
+                        % aterm2String(name));
+                    mkThunk(v, env2, def);
+                } else {
+                    attrsUsed++;
+                    v.type = tCopy;
+                    v.val = &j->second;
+                }
+            }
+
+            /* 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 (ellipsis == eFalse && attrsUsed != vArg->attrs->size())
+                throw TypeError("function called with unexpected argument");
+        }
+
+        else abort();
+        
+        eval(env2, v.lambda.body, v);
+        return;
+    }
+
+    Expr attrs;
+    if (matchWith(e, attrs, body, pos)) {
+        Env & env2(allocEnv());
+        env2.up = &env;
+
+        Value & vAttrs = env2.bindings[sWith];
+        nrValues++;
+        eval(env, attrs, vAttrs);
+        forceAttrs(vAttrs);
+        
+        eval(env2, body, v);
+        return;
+    }
+
+    if (matchList(e, es)) {
+        v.type = tList;
+        v.list.length = ATgetLength(es);
+        v.list.elems = allocValues(v.list.length);
+        for (unsigned int n = 0; n < v.list.length; ++n, es = ATgetNext(es))
+            mkThunk(v.list.elems[n], env, ATgetFirst(es));
+        return;
+    }
+
+    if (matchOpEq(e, e1, e2)) {
+        Value v1; eval(env, e1, v1);
+        Value v2; eval(env, e2, v2);
+        mkBool(v, eqValues(v1, v2));
+        return;
+    }
+
+    if (matchOpNEq(e, e1, e2)) {
+        Value v1; eval(env, e1, v1);
+        Value v2; eval(env, e2, v2);
+        mkBool(v, !eqValues(v1, v2));
+        return;
+    }
+
+    if (matchOpConcat(e, e1, e2)) {
+        Value v1; eval(env, e1, v1);
+        forceList(v1);
+        Value v2; eval(env, e2, v2);
+        forceList(v2);
+        v.type = tList;
+        v.list.length = v1.list.length + v2.list.length;
+        v.list.elems = allocValues(v.list.length);
+        /* !!! This loses sharing with the original lists.  We could
+           use a tCopy node, but that would use more memory. */
+        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];
+        return;
+    }
+
+    if (matchConcatStrings(e, es)) {
+        unsigned int n = ATgetLength(es), j = 0;
+        Value vs[n];
+        unsigned int len = 0;
+        for (ATermIterator i(es); i; ++i, ++j) {
+            eval(env, *i, vs[j]);
+            if (vs[j].type != tString) throw TypeError("string expected");
+            len += strlen(vs[j].string.s);
+        }
+        char * s = new char[len + 1], * t = s;
+        for (unsigned int i = 0; i < j; ++i) {
+            strcpy(t, vs[i].string.s);
+            t += strlen(vs[i].string.s);
+        }
+        *t = 0;
+        mkString(v, s);
+        return;
+    }
+
+    Expr e3;
+    if (matchIf(e, e1, e2, e3)) {
+        eval(env, evalBool(env, e1) ? e2 : e3, v);
+        return;
+    }
+
+    if (matchOpOr(e, e1, e2)) {
+        mkBool(v, evalBool(env, e1) || evalBool(env, e2));
+        return;
+    }
+
+    throw Error("unsupported term");
+}
+
+
+void EvalState::eval(Expr e, Value & v)
+{
+    eval(baseEnv, e, v);
+}
+
+
+bool EvalState::evalBool(Env & env, Expr e)
+{
+    Value v;
+    eval(env, e, v);
+    if (v.type != tBool)
+        throw TypeError(format("value is %1% while a Boolean was expected") % showType(v));
+    return v.boolean;
+}
+
+
+void EvalState::strictEval(Env & env, Expr e, Value & v)
+{
+    eval(env, e, v);
+    
+    if (v.type == tAttrs) {
+        foreach (Bindings::iterator, i, *v.attrs)
+            forceValue(i->second);
+    }
+    
+    else if (v.type == tList) {
+        for (unsigned int n = 0; n < v.list.length; ++n)
+            forceValue(v.list.elems[n]);
+    }
+}
+
+
+void EvalState::strictEval(Expr e, Value & v)
+{
+    strictEval(baseEnv, e, v);
+}
+
+
+void EvalState::forceValue(Value & v)
+{
+    if (v.type == tThunk) {
+        v.type = tBlackhole;
+        eval(*v.thunk.env, v.thunk.expr, v);
+    }
+    else if (v.type == tCopy) {
+        forceValue(*v.val);
+        v = *v.val;
+    }
+    else if (v.type == tBlackhole)
+        throw EvalError("infinite recursion encountered");
+}
+
+
+int EvalState::forceInt(Value & v)
+{
+    forceValue(v);
+    if (v.type != tInt)
+        throw TypeError(format("value is %1% while an integer was expected") % showType(v));
+    return v.integer;
+}
+
+
+void EvalState::forceAttrs(Value & v)
+{
+    forceValue(v);
+    if (v.type != tAttrs)
+        throw TypeError(format("value is %1% while an attribute set was expected") % showType(v));
+}
+
+
+void EvalState::forceList(Value & v)
+{
+    forceValue(v);
+    if (v.type != tList)
+        throw TypeError(format("value is %1% while a list was expected") % showType(v));
+}
+
+
+bool EvalState::eqValues(Value & v1, Value & v2)
+{
+    forceValue(v1);
+    forceValue(v2);
+
+    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:
+            /* !!! contexts */
+            return strcmp(v1.string.s, v2.string.s) == 0;
+
+        case tList:
+            if (v2.type != tList || 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 (v2.type != tAttrs || 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 (!eqValues(i->second, j->second)) return false;
+            return true;
+        }
+
+        default:
+            throw Error("cannot compare given values");
+    }
+}
+
+
+#if 0
 /* 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
@@ -683,9 +1216,6 @@ LocalNoInline(bool areEqual(EvalState & state, Expr e1, Expr e2))
 }
 
 
-static char * deepestStack = (char *) -1; /* for measuring stack usage */
-
-
 Expr evalExpr2(EvalState & state, Expr e)
 {
     /* When changing this function, make sure that you don't cause a
@@ -884,23 +1414,19 @@ Expr strictEvalExpr(EvalState & state, Expr e)
     ATermMap strictNormalForms;
     return strictEvalExpr(state, e, strictNormalForms);
 }
+#endif
 
 
-/* Yes, this is a really bad idea... */
-extern "C" {
-    unsigned long AT_calcAllocatedSize();
-}
-
 void printEvalStats(EvalState & state)
 {
     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));
+        format("evaluated %1% expressions, used %2% bytes of stack space, allocated %3% values, allocated %4% environments")
+        % state.nrEvaluated
+        % (&x - deepestStack)
+        % state.nrValues
+        % state.nrEnvs);
     if (showStats)
         printATermMapStats();
 }
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index fed6d34726..8ca997f140 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -11,7 +11,101 @@ namespace nix {
 
 
 class Hash;
-    
+class EvalState;
+struct Env;
+struct Value;
+
+typedef ATerm Sym;
+
+typedef std::map<Sym, Value> Bindings;
+
+
+struct Env
+{
+    Env * up;
+    Bindings bindings;
+};
+
+
+typedef enum {
+    tInt = 1,
+    tBool,
+    tString,
+    tPath,
+    tNull,
+    tAttrs,
+    tList,
+    tThunk,
+    tLambda,
+    tCopy,
+    tBlackhole,
+    tPrimOp,
+    tPrimOpApp,
+} ValueType;
+
+
+typedef void (* PrimOp) (EvalState & state, Value * * args, Value & v);
+
+
+struct Value
+{
+    ValueType type;
+    union 
+    {
+        int integer;
+        bool boolean;
+        struct {
+            const char * s;
+            const char * * context;
+        } string;
+        Bindings * attrs;
+        struct {
+            unsigned int length;
+            Value * elems;
+        } list;
+        struct {
+            Env * env;
+            Expr expr;
+        } thunk;
+        struct {
+            Env * env;
+            Pattern pat;
+            Expr body;
+        } lambda;
+        Value * val;
+        struct {
+            PrimOp fun;
+            unsigned int arity;
+        } primOp;
+        struct {
+            Value * left, * right;
+            unsigned int argsLeft;
+        } primOpApp;
+    };
+};
+
+
+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 mkString(Value & v, const char * s)
+{
+    v.type = tString;
+    v.string.s = s;
+    v.string.context = 0;
+}
+
 
 typedef std::map<Path, PathSet> DrvRoots;
 typedef std::map<Path, Hash> DrvHashes;
@@ -22,32 +116,69 @@ 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 
 {
-    ATermMap normalForms;
-    ATermMap primOps;
     DrvRoots drvRoots;
     DrvHashes drvHashes; /* normalised derivation hashes */
     SrcToStore srcToStore; 
 
-    unsigned int nrEvaluated;
-    unsigned int nrCached;
+    unsigned long nrValues;
+    unsigned long nrEnvs;
+    unsigned long nrEvaluated;
 
     bool allowUnsafeEquality;
 
     EvalState();
 
-    void addPrimOps();
+    /* 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);
+
+    /* Evaluate an expression, and recursively evaluate list elements
+       and attributes. */
+    void strictEval(Expr e, Value & v);
+    void strictEval(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.  Otherwise, this is a no-op. */
+    void forceValue(Value & v);
+
+    /* Force `v', and then verify that it has the expected type. */
+    int forceInt(Value & v);
+    void forceAttrs(Value & v);
+    void forceList(Value & v);
+
+private:
+
+    /* The base environment, containing the builtin functions and
+       values. */
+    Env & baseEnv;
+
+    void createBaseEnv();
+    
     void addPrimOp(const string & name,
         unsigned int arity, PrimOp primOp);
+
+    /* Do a deep equality test between two values.  That is, list
+       elements and attributes are compared recursively. */
+    bool eqValues(Value & v1, Value & v2);
+
+    /* Allocation primitives. */
+    Value * allocValues(unsigned int count);
+    Env & allocEnv();
 };
 
 
+#if 0
 /* Evaluate an expression to normal form. */
 Expr evalExpr(EvalState & state, Expr e);
 
@@ -86,11 +217,12 @@ Path coerceToPath(EvalState & state, Expr e, PathSet & context);
    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);
+#endif
 
 /* Print statistics. */
 void printEvalStats(EvalState & state);
 
- 
+
 }
 
 
diff --git a/src/libexpr/get-drvs.cc b/src/libexpr/get-drvs.cc
index 1442d7988b..26ce6e71cf 100644
--- a/src/libexpr/get-drvs.cc
+++ b/src/libexpr/get-drvs.cc
@@ -6,6 +6,7 @@
 namespace nix {
 
 
+#if 0
 string DrvInfo::queryDrvPath(EvalState & state) const
 {
     if (drvPath == "") {
@@ -256,6 +257,7 @@ void getDerivations(EvalState & state, Expr e, const string & pathPrefix,
     Exprs doneExprs;
     getDerivations(state, e, pathPrefix, autoArgs, drvs, doneExprs);
 }
+#endif
 
  
 }
diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index e55dfd76f5..2f0c9db3f3 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -375,7 +375,7 @@ expr_op
   | 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 '+' expr_op { $$ = makeConcatStrings(ATmakeList2($1, $3)); }
   | expr_op CONCAT expr_op { $$ = makeOpConcat($1, $3); }
   | expr_app
   ;
@@ -513,7 +513,7 @@ static Expr parse(EvalState & state,
     if (res) throw ParseError(data.error);
 
     try {
-        checkVarDefs(state.primOps, data.result);
+        // !!! checkVarDefs(state.primOps, data.result);
     } catch (Error & e) {
         throw ParseError(format("%1%, in `%2%'") % e.msg() % path);
     }
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 52292f3f84..a24f40be67 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -19,6 +19,7 @@
 namespace nix {
 
 
+#if 0
 /*************************************************************
  * Constants
  *************************************************************/
@@ -895,18 +896,21 @@ static Expr prim_isList(EvalState & state, const ATermVector & args)
     ATermList list;
     return makeBool(matchList(evalExpr(state, args[0]), list));
 }
+#endif
 
 
 /* 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];
 }
 
 
+#if 0
 /* Return a list consisting of everything but the the first element of
    a list. */
 static Expr prim_tail(EvalState & state, const ATermVector & args)
@@ -938,6 +942,7 @@ static Expr prim_length(EvalState & state, const ATermVector & args)
     ATermList list = evalList(state, args[0]);
     return makeInt(ATgetLength(list));
 }
+#endif
 
 
 /*************************************************************
@@ -945,14 +950,13 @@ 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]));
 }
 
 
+#if 0
 static Expr prim_sub(EvalState & state, const ATermVector & args)
 {
     int i1 = evalInt(state, args[0]);
@@ -1102,6 +1106,7 @@ static Expr prim_compareVersions(EvalState & state, const ATermVector & args)
     int d = compareVersions(version1, version2);
     return makeInt(d);
 }
+#endif
 
 
 /*************************************************************
@@ -1109,14 +1114,31 @@ static Expr prim_compareVersions(EvalState & state, const ATermVector & args)
  *************************************************************/
 
 
-void EvalState::addPrimOps()
+void EvalState::createBaseEnv()
 {
-    addPrimOp("builtins", 0, prim_builtins);
-        
+    baseEnv.up = 0;
+
+    {   Value & v = baseEnv.bindings[toATerm("builtins")];
+        v.type = tAttrs;
+        v.attrs = new Bindings;
+    }
+    
+    /* Add global constants such as `true' to the base environment. */
+    {   Value & v = baseEnv.bindings[toATerm("true")];
+        mkBool(v, true);
+    }
+    {   Value & v = baseEnv.bindings[toATerm("false")];
+        mkBool(v, false);
+    }
+    {   Value & v = baseEnv.bindings[toATerm("null")];
+        v.type = tNull;
+    }
+    {   Value & v = (*baseEnv.bindings[toATerm("builtins")].attrs)[toATerm("currentSystem")];
+        mkString(v, thisSystem.c_str()); // !!! copy string
+    }
+
+#if 0    
     // 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);
 
@@ -1134,7 +1156,6 @@ void EvalState::addPrimOps()
     addPrimOp("__tryEval", 1, prim_tryEval);
     addPrimOp("__getEnv", 1, prim_getEnv);
     addPrimOp("__trace", 2, prim_trace);
-
     
     // Expr <-> String
     addPrimOp("__exprToString", 1, prim_exprToString);
@@ -1169,13 +1190,17 @@ void EvalState::addPrimOps()
 
     // Lists
     addPrimOp("__isList", 1, prim_isList);
+#endif
     addPrimOp("__head", 1, prim_head);
+#if 0
     addPrimOp("__tail", 1, prim_tail);
     addPrimOp("map", 2, prim_map);
     addPrimOp("__length", 1, prim_length);
-
+#endif
+    
     // Integer arithmetic
     addPrimOp("__add", 2, prim_add);
+#if 0
     addPrimOp("__sub", 2, prim_sub);
     addPrimOp("__mul", 2, prim_mul);
     addPrimOp("__div", 2, prim_div);
@@ -1191,6 +1216,7 @@ void EvalState::addPrimOps()
     // Versions
     addPrimOp("__parseDrvName", 1, prim_parseDrvName);
     addPrimOp("__compareVersions", 2, prim_compareVersions);
+#endif
 }