* Keep attribute sets in sorted order to speed up attribute lookups.

* Simplify the representation of attributes in the AST.
* Change the behaviour of listToAttrs() in case of duplicate names.

11 files changed, 184 insertions, 146 deletions

diff --git a/src/libexpr/common-opts.cc b/src/libexpr/common-opts.cc
index 6b393c07df50..c364aa9cb599 100644
--- a/src/libexpr/common-opts.cc
+++ b/src/libexpr/common-opts.cc
@@ -20,14 +20,17 @@ bool parseOptionArg(const string & arg, Strings::iterator & i,
     if (i == argsEnd) throw error;
     string value = *i++;
 
+    /* !!! check for duplicates! */
     Value * v = state.allocValue();
-    autoArgs[state.symbols.create(name)].value = v;
+    autoArgs.push_back(Attr(state.symbols.create(name), v));
 
     if (arg == "--arg")
         state.mkThunk_(*v, parseExprFromString(state, value, absPath(".")));
     else
         mkString(*v, value);
-    
+
+    autoArgs.sort(); // !!! inefficient
+
     return true;
 }
 
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 124cf6498f06..4aa8fc1e44b5 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -34,18 +34,16 @@ namespace nix {
 
 Bindings::iterator Bindings::find(const Symbol & name)
 {
-    iterator i = begin();
-    for ( ; i != end() && i->name != name; ++i) ;
-    return i;
+    Attr key(name, 0);
+    iterator i = lower_bound(begin(), end(), key);
+    if (i != end() && i->name == name) return i;
+    return end();
 }
 
 
-Attr & Bindings::operator [] (const Symbol & name)
+void Bindings::sort()
 {
-    iterator i = find(name);
-    if (i != end()) return *i;
-    push_back(Attr(name, 0));
-    return back();
+    std::sort(begin(), end());
 }
     
 
@@ -178,12 +176,12 @@ void EvalState::addPrimOp(const string & name,
 {
     Value * v = allocValue();
     string name2 = string(name, 0, 2) == "__" ? string(name, 2) : name;
-    Symbol sym = symbols.create(name);
+    Symbol sym = symbols.create(name2);
     v->type = tPrimOp;
     v->primOp = NEW PrimOp(primOp, arity, sym);
-    staticBaseEnv.vars[sym] = baseEnvDispl;
+    staticBaseEnv.vars[symbols.create(name)] = baseEnvDispl;
     baseEnv.values[baseEnvDispl++] = v;
-    baseEnv.values[0]->attrs->push_back(Attr(symbols.create(name2), v));
+    baseEnv.values[0]->attrs->push_back(Attr(sym, v));
 }
 
 
@@ -506,32 +504,38 @@ void ExprPath::eval(EvalState & state, Env & env, Value & v)
 
 void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
 {
-    state.mkAttrs(v);
+    state.mkAttrs(v); // !!! reserve size
 
     if (recursive) {
         /* Create a new environment that contains the attributes in
            this `rec'. */
-        Env & env2(state.allocEnv(attrs.size() + inherited.size()));
+        Env & env2(state.allocEnv(attrs.size()));
         env2.up = &env;
 
+        AttrDefs::iterator overrides = attrs.find(state.sOverrides);
+        bool hasOverrides = overrides != attrs.end();
+
+        /* The recursive attributes are evaluated in the new
+           environment, while the inherited attributes are evaluated
+           in the original environment. */
         unsigned int displ = 0;
+        foreach (AttrDefs::iterator, i, attrs)
+            if (i->second.inherited) {
+                /* !!! handle overrides? */
+                Value * vAttr = state.lookupVar(&env, i->second.var);
+                env2.values[displ++] = vAttr;
+                v.attrs->push_back(Attr(i->first, vAttr, &i->second.pos));
+            } else {
+                Value * vAttr;
+                if (hasOverrides) {
+                    vAttr = state.allocValue();
+                    mkThunk(*vAttr, env2, i->second.e);
+                } else
+                    vAttr = state.maybeThunk(env2, i->second.e);
+                env2.values[displ++] = vAttr;
+                v.attrs->push_back(Attr(i->first, vAttr, &i->second.pos));
+            }
         
-        /* The recursive attributes are evaluated in the new
-           environment. */
-        foreach (Attrs::iterator, i, attrs) {
-            Value * vAttr = state.maybeThunk(env2, i->second.first);
-            env2.values[displ++] = vAttr;
-            v.attrs->push_back(nix::Attr(i->first, vAttr, &i->second.second));
-        }
-
-        /* The inherited attributes, on the other hand, are
-           evaluated in the original environment. */
-        foreach (list<Inherited>::iterator, i, inherited) {
-            Value * vAttr = state.lookupVar(&env, i->first);
-            env2.values[displ++] = vAttr;
-            v.attrs->push_back(nix::Attr(i->first.name, vAttr, &i->second));
-        }
-
         /* 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
@@ -540,30 +544,27 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
            still reference the original value, because that value has
            been substituted into the bodies of the other attributes.
            Hence we need __overrides.) */
-        Bindings::iterator overrides = v.attrs->find(state.sOverrides);
-        if (overrides != v.attrs->end()) {
-            state.forceAttrs(*overrides->value);
-            foreach (Bindings::iterator, i, *overrides->value->attrs) {
-                nix::Attr & a = (*v.attrs)[i->name];
-                if (a.value)
-                    env2.values[displs[i->name]] = i->value;
-                a = *i;
+        if (hasOverrides) {
+            Value * vOverrides = (*v.attrs)[overrides->second.displ].value;
+            state.forceAttrs(*vOverrides);
+            foreach (Bindings::iterator, i, *vOverrides->attrs) {
+                AttrDefs::iterator j = attrs.find(i->name);
+                if (j != attrs.end()) {
+                    (*v.attrs)[j->second.displ] = *i;
+                    env2.values[j->second.displ] = i->value;
+                } else
+                    v.attrs->push_back(*i);
             }
+            v.attrs->sort();
         }
     }
 
     else {
-        foreach (Attrs::iterator, i, attrs) {
-            nix::Attr & a = (*v.attrs)[i->first];
-            a.value = state.maybeThunk(env, i->second.first);
-            a.pos = &i->second.second;
-        }
-
-        foreach (list<Inherited>::iterator, i, inherited) {
-            nix::Attr & a = (*v.attrs)[i->first.name];
-            a.value = state.lookupVar(&env, i->first);
-            a.pos = &i->second;
-        }
+        foreach (AttrDefs::iterator, i, attrs)
+            if (i->second.inherited)
+                v.attrs->push_back(Attr(i->first, state.lookupVar(&env, i->second.var), &i->second.pos));
+            else
+                v.attrs->push_back(Attr(i->first, state.maybeThunk(env, i->second.e), &i->second.pos));
     }
 }
 
@@ -572,20 +573,18 @@ void ExprLet::eval(EvalState & state, Env & env, Value & v)
 {
     /* Create a new environment that contains the attributes in this
        `let'. */
-    Env & env2(state.allocEnv(attrs->attrs.size() + attrs->inherited.size()));
+    Env & env2(state.allocEnv(attrs->attrs.size()));
     env2.up = &env;
 
-    unsigned int displ = 0;
-
-    /* The recursive attributes are evaluated in the new
+    /* The recursive attributes are evaluated in the new environment,
+       while the inherited attributes are evaluated in the original
        environment. */
-    foreach (ExprAttrs::Attrs::iterator, i, attrs->attrs)
-        env2.values[displ++] = state.maybeThunk(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)
-        env2.values[displ++] = state.lookupVar(&env, i->first);
+    unsigned int displ = 0;
+    foreach (ExprAttrs::AttrDefs::iterator, i, attrs->attrs)
+        if (i->second.inherited)
+            env2.values[displ++] = state.lookupVar(&env, i->second.var);
+        else
+            env2.values[displ++] = state.maybeThunk(env2, i->second.e);
 
     state.eval(env2, body, v);
 }
@@ -736,7 +735,7 @@ void EvalState::callFunction(Value & fun, Value & arg, Value & v)
            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())
+        if (!fun.lambda.fun->formals->ellipsis && attrsUsed != arg.attrs->size()) 
             throwTypeError("function at %1% called with unexpected argument", fun.lambda.fun->pos);
     }
 
@@ -764,11 +763,13 @@ void EvalState::autoCallFunction(Bindings & args, Value & fun, Value & res)
     foreach (Formals::Formals_::iterator, i, fun.lambda.fun->formals->formals) {
         Bindings::iterator j = args.find(i->name);
         if (j != args.end())
-            (*actualArgs.attrs)[i->name] = *j;
+            actualArgs.attrs->push_back(*j);
         else if (!i->def)
             throwTypeError("cannot auto-call a function that has an argument without a default value (`%1%')", i->name);
     }
 
+    actualArgs.attrs->sort();
+
     callFunction(fun, actualArgs, res);
 }
 
@@ -851,12 +852,28 @@ void ExprOpUpdate::eval(EvalState & state, Env & env, Value & v)
     if (v1.attrs->size() == 0) { v = v2; return; }
     if (v2.attrs->size() == 0) { v = v1; return; }
 
-    state.cloneAttrs(v1, v);
+    state.mkAttrs(v);
+
+    /* Merge the attribute sets, preferring values from the second
+       set.  Make sure to keep the resulting vector in sorted
+       order. */
+    Bindings::iterator i = v1.attrs->begin();
+    Bindings::iterator j = v2.attrs->begin();
 
-    /* !!! fix */
-    foreach (Bindings::iterator, i, *v2.attrs)
-        (*v.attrs)[i->name] = *i;
+    while (i != v1.attrs->end() && j != v2.attrs->end()) {
+        if (i->name == j->name) {
+            v.attrs->push_back(*j);
+            ++i; ++j;
+        }
+        else if (i->name < j->name)
+            v.attrs->push_back(*i++);
+        else
+            v.attrs->push_back(*j++);
+    }
 
+    while (i != v1.attrs->end()) v.attrs->push_back(*i++);
+    while (j != v2.attrs->end()) v.attrs->push_back(*j++);
+    
     state.nrOpUpdateValuesCopied += v.attrs->size();
 }
 
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index e1aa69dd38d2..7f801d1125fb 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -34,7 +34,7 @@ class Bindings : public BindingsBase
 {
 public:
     iterator find(const Symbol & name);
-    Attr & operator [] (const Symbol & name);
+    void sort();
 };
 
 
@@ -142,6 +142,10 @@ struct Attr
     Attr(Symbol name, Value * value, Pos * pos = &noPos)
         : name(name), value(value), pos(pos) { };
     Attr() : pos(&noPos) { };
+    bool operator < (const Attr & a) const
+    {
+        return name < a.name;
+    }
 };
 
 
diff --git a/src/libexpr/get-drvs.cc b/src/libexpr/get-drvs.cc
index 312c2cd405e6..a28a705d22d1 100644
--- a/src/libexpr/get-drvs.cc
+++ b/src/libexpr/get-drvs.cc
@@ -168,7 +168,7 @@ static void getDerivations(EvalState & state, Value & vIn,
         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);
+            Value & v2(*v.attrs->find(i->second)->value);
             if (combineChannels)
                 getDerivations(state, v2, pathPrefix2, autoArgs, drvs, done);
             else if (getDerivation(state, v2, pathPrefix2, drvs, done)) {
diff --git a/src/libexpr/nixexpr.cc b/src/libexpr/nixexpr.cc
index 9f2ea78831f2..147f50853e9d 100644
--- a/src/libexpr/nixexpr.cc
+++ b/src/libexpr/nixexpr.cc
@@ -55,10 +55,11 @@ 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 << "; ";
+    foreach (AttrDefs::iterator, i, attrs)
+        if (i->second.inherited)
+            str << "inherit " << i->first << " " << "; ";
+        else
+            str << i->first << " = " << *i->second.e << "; ";
     str << "}";
 }
 
@@ -91,10 +92,11 @@ void ExprLambda::show(std::ostream & str)
 void ExprLet::show(std::ostream & str)
 {
     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 << "; ";
+    foreach (ExprAttrs::AttrDefs::iterator, i, attrs->attrs)
+        if (i->second.inherited)
+            str << "inherit " << i->first << "; ";
+        else
+            str << i->first << " = " << *i->second.e << "; ";
     str << "in " << *body;
 }
 
@@ -211,26 +213,18 @@ void ExprAttrs::bindVars(const StaticEnv & env)
         StaticEnv newEnv(false, &env);
     
         unsigned int displ = 0;
-
-        foreach (ExprAttrs::Attrs::iterator, i, attrs)
-            displs[i->first] = newEnv.vars[i->first] = displ++;
-
-        foreach (list<Inherited>::iterator, i, inherited) {
-            displs[i->first.name] = newEnv.vars[i->first.name] = displ++;
-            i->first.bind(env);
-        }
-
-        foreach (ExprAttrs::Attrs::iterator, i, attrs)
-            i->second.first->bindVars(newEnv);
+        foreach (AttrDefs::iterator, i, attrs)
+            newEnv.vars[i->first] = i->second.displ = displ++;
+        
+        foreach (AttrDefs::iterator, i, attrs)
+            if (i->second.inherited) i->second.var.bind(env);
+            else i->second.e->bindVars(newEnv);
     }
 
-    else {
-        foreach (ExprAttrs::Attrs::iterator, i, attrs)
-            i->second.first->bindVars(env);
-
-        foreach (list<Inherited>::iterator, i, inherited)
-            i->first.bind(env);
-    }
+    else
+        foreach (AttrDefs::iterator, i, attrs)
+            if (i->second.inherited) i->second.var.bind(env);
+            else i->second.e->bindVars(env);
 }
 
 void ExprList::bindVars(const StaticEnv & env)
@@ -263,17 +257,12 @@ 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);
-    }
-
-    foreach (ExprAttrs::Attrs::iterator, i, attrs->attrs)
-        i->second.first->bindVars(newEnv);
+    foreach (ExprAttrs::AttrDefs::iterator, i, attrs->attrs)
+        newEnv.vars[i->first] = i->second.displ = displ++;
+    
+    foreach (ExprAttrs::AttrDefs::iterator, i, attrs->attrs)
+        if (i->second.inherited) i->second.var.bind(env);
+        else i->second.e->bindVars(newEnv);
     
     body->bindVars(newEnv);
 }
diff --git a/src/libexpr/nixexpr.hh b/src/libexpr/nixexpr.hh
index 1aa3df3689a6..8f976f1de8f9 100644
--- a/src/libexpr/nixexpr.hh
+++ b/src/libexpr/nixexpr.hh
@@ -101,6 +101,7 @@ struct VarRef
     unsigned int level;
     unsigned int displ;
 
+    VarRef() { };
     VarRef(const Symbol & name) : name(name) { };
     void bind(const StaticEnv & env);
 };
@@ -131,13 +132,18 @@ struct ExprOpHasAttr : Expr
 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
-    std::map<Symbol, unsigned int> displs;
+    struct AttrDef {
+        bool inherited;
+        Expr * e; // if not inherited
+        VarRef var; // if inherited
+        Pos pos;
+        unsigned int displ; // displacement
+        AttrDef(Expr * e, const Pos & pos) : inherited(false), e(e), pos(pos) { };
+        AttrDef(const Symbol & name, const Pos & pos) : inherited(true), var(name), pos(pos) { };
+        AttrDef() { };
+    };
+    typedef std::map<Symbol, AttrDef> AttrDefs;
+    AttrDefs attrs;
     ExprAttrs() : recursive(false) { };
     COMMON_METHODS
 };
diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index 3a72a4ade257..c6d29b6ca8bd 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -93,20 +93,20 @@ static void addAttr(ExprAttrs * attrs, const vector<Symbol> & attrPath,
     unsigned int n = 0;
     foreach (vector<Symbol>::const_iterator, i, attrPath) {
         n++;
-        ExprAttrs::Attrs::iterator j = attrs->attrs.find(*i);
+        ExprAttrs::AttrDefs::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;
+            if (!j->second.inherited) {
+                ExprAttrs * attrs2 = dynamic_cast<ExprAttrs *>(j->second.e);
+                if (!attrs2 || n == attrPath.size()) dupAttr(attrPath, pos, j->second.pos);
+                attrs = attrs2;
+            } else
+                dupAttr(attrPath, pos, j->second.pos);
         } 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);
+                attrs->attrs[*i] = ExprAttrs::AttrDef(e, pos);
             else {
                 ExprAttrs * nested = new ExprAttrs;
-                attrs->attrs[*i] = ExprAttrs::Attr(nested, pos);
+                attrs->attrs[*i] = ExprAttrs::AttrDef(nested, pos);
                 attrs = nested;
             }
         }
@@ -383,21 +383,19 @@ binds
   | binds INHERIT ids ';'
     { $$ = $1;
       foreach (vector<Symbol>::iterator, i, *$3) {
-          if ($$->attrNames.find(*i) != $$->attrNames.end())
-              dupAttr(*i, makeCurPos(@3, data), $$->attrNames[*i]);
+          if ($$->attrs.find(*i) != $$->attrs.end())
+              dupAttr(*i, makeCurPos(@3, data), $$->attrs[*i].pos);
           Pos pos = makeCurPos(@3, data);
-          $$->inherited.push_back(ExprAttrs::Inherited(*i, pos));
-          $$->attrNames[*i] = pos;
+          $$->attrs[*i] = ExprAttrs::AttrDef(*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);
+          if ($$->attrs.find(*i) != $$->attrs.end())
+              dupAttr(*i, makeCurPos(@6, data), $$->attrs[*i].pos);
+          $$->attrs[*i] = ExprAttrs::AttrDef(new ExprSelect($4, *i), makeCurPos(@6, data));
       }}
 
   | { $$ = new ExprAttrs; }
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 3e32dd3ffc0e..7c713f384f33 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -209,14 +209,13 @@ static void prim_tryEval(EvalState & state, Value * * args, Value & v)
     state.mkAttrs(v);
     try {
         state.forceValue(*args[0]);
-        printMsg(lvlError, format("%1%") % *args[0]);
-        (*v.attrs)[state.symbols.create("value")].value = args[0];
+        v.attrs->push_back(Attr(state.symbols.create("value"), args[0]));
         mkBool(*state.allocAttr(v, state.symbols.create("success")), true);
-        printMsg(lvlError, format("%1%") % v);
     } catch (AssertionError & e) {
         mkBool(*state.allocAttr(v, state.symbols.create("value")), false);
         mkBool(*state.allocAttr(v, state.symbols.create("success")), false);
     }
+    v.attrs->sort();
 }
 
 
@@ -488,6 +487,7 @@ static void prim_derivationStrict(EvalState & state, Value * * args, Value & v)
     state.mkAttrs(v);
     mkString(*state.allocAttr(v, state.sOutPath), outPath, singleton<PathSet>(drvPath));
     mkString(*state.allocAttr(v, state.sDrvPath), drvPath, singleton<PathSet>("=" + drvPath));
+    v.attrs->sort();
 }
 
 
@@ -742,7 +742,9 @@ static void prim_removeAttrs(EvalState & state, Value * * args, Value & v)
         names.insert(state.symbols.create(args[1]->list.elems[i]->string.s));
     }
 
-    /* Copy all attributes not in that set. */
+    /* Copy all attributes not in that set.  Note that we don't need
+       to sort v.attrs because it's a subset of an already sorted
+       vector. */
     state.mkAttrs(v);
     foreach (Bindings::iterator, i, *args[0]->attrs) {
         if (names.find(i->name) == names.end())
@@ -761,6 +763,8 @@ static void prim_listToAttrs(EvalState & state, Value * * args, Value & v)
 
     state.mkAttrs(v);
 
+    std::set<Symbol> seen;
+
     for (unsigned int i = 0; i < args[0]->list.length; ++i) {
         Value & v2(*args[0]->list.elems[i]);
         state.forceAttrs(v2);
@@ -774,10 +778,15 @@ static void prim_listToAttrs(EvalState & state, Value * * args, Value & v)
         if (j2 == v2.attrs->end())
             throw TypeError("`value' attribute missing in a call to `listToAttrs'");
 
-        Attr & a = (*v.attrs)[state.symbols.create(name)];
-        a.value = j2->value;
-        a.pos = j2->pos;
+        Symbol sym = state.symbols.create(name);
+        if (seen.find(sym) == seen.end()) {
+            v.attrs->push_back(Attr(sym, j2->value, j2->pos));
+            seen.insert(sym);
+        }
+        /* !!! Throw an error if `name' already exists? */
     }
+
+    v.attrs->sort();
 }
 
 
@@ -825,6 +834,8 @@ static void prim_functionArgs(EvalState & state, Value * * args, Value & v)
     foreach (Formals::Formals_::iterator, i, args[0]->lambda.fun->formals->formals)
         // !!! should optimise booleans (allocate only once)
         mkBool(*state.allocAttr(v, i->name), i->def);
+
+    v.attrs->sort();
 }
 
 
@@ -1007,6 +1018,7 @@ static void prim_parseDrvName(EvalState & state, Value * * args, Value & v)
     state.mkAttrs(v);
     mkString(*state.allocAttr(v, state.sName), parsed.name);
     mkString(*state.allocAttr(v, state.symbols.create("version")), parsed.version);
+    v.attrs->sort();
 }
 
 
@@ -1119,7 +1131,11 @@ void EvalState::createBaseEnv()
 
     // Versions
     addPrimOp("__parseDrvName", 1, prim_parseDrvName);
-    addPrimOp("__compareVersions", 2, prim_compareVersions);    
+    addPrimOp("__compareVersions", 2, prim_compareVersions);
+
+    /* Now that we've added all primops, sort the `builtins' attribute
+       set, because attribute lookups expect it to be sorted. */
+    baseEnv.values[0]->attrs->sort();
 }
 
 
diff --git a/src/libexpr/value-to-xml.cc b/src/libexpr/value-to-xml.cc
index 4f9b62d5f15e..bc63f776269c 100644
--- a/src/libexpr/value-to-xml.cc
+++ b/src/libexpr/value-to-xml.cc
@@ -37,7 +37,7 @@ static void showAttrs(EvalState & state, bool strict, bool location,
         names.insert(i->name);
     
     foreach (StringSet::iterator, i, names) {
-        Attr & a(attrs[state.symbols.create(*i)]);
+        Attr & a(*attrs.find(state.symbols.create(*i)));
         
         XMLAttrs xmlAttrs;
         xmlAttrs["name"] = *i;
diff --git a/src/nix-env/nix-env.cc b/src/nix-env/nix-env.cc
index 4895c68e94a8..58bc9af12598 100644
--- a/src/nix-env/nix-env.cc
+++ b/src/nix-env/nix-env.cc
@@ -132,7 +132,7 @@ static void getAllExprs(EvalState & state,
             if (hasSuffix(attrName, ".nix"))
                 attrName = string(attrName, 0, attrName.size() - 4);
             attrs.attrs[state.symbols.create(attrName)] =
-                ExprAttrs::Attr(parseExprFromFile(state, absPath(path2)), noPos);
+                ExprAttrs::AttrDef(parseExprFromFile(state, absPath(path2)), noPos);
         }
         else
             /* `path2' is a directory (with no default.nix in it);
@@ -154,7 +154,7 @@ static Expr * loadSourceExpr(EvalState & state, const Path & path)
        some system-wide directory). */
     ExprAttrs * attrs = new ExprAttrs;
     attrs->attrs[state.symbols.create("_combineChannels")] =
-        ExprAttrs::Attr(new ExprList(), noPos);
+        ExprAttrs::AttrDef(new ExprList(), noPos);
     getAllExprs(state, path, *attrs);
     return attrs;
 }
diff --git a/src/nix-env/user-env.cc b/src/nix-env/user-env.cc
index 34e00b7c2e61..acd866197c7c 100644
--- a/src/nix-env/user-env.cc
+++ b/src/nix-env/user-env.cc
@@ -69,13 +69,14 @@ bool createUserEnv(EvalState & state, DrvInfos & elems,
         mkString(*state.allocAttr(v, state.sOutPath), i->queryOutPath(state));
         if (drvPath != "")
             mkString(*state.allocAttr(v, state.sDrvPath), i->queryDrvPath(state));
-        
-        state.mkAttrs(*state.allocAttr(v, state.sMeta));
-        
+
+        Value & vMeta = *state.allocAttr(v, state.sMeta);
+        state.mkAttrs(vMeta);
+
         MetaInfo meta = i->queryMetaInfo(state);
 
         foreach (MetaInfo::const_iterator, j, meta) {
-            Value & v2(*state.allocAttr(*(*v.attrs)[state.sMeta].value, state.symbols.create(j->first)));
+            Value & v2(*state.allocAttr(vMeta, state.symbols.create(j->first)));
             switch (j->second.type) {
                 case MetaValue::tpInt: mkInt(v2, j->second.intValue); break;
                 case MetaValue::tpString: mkString(v2, j->second.stringValue); break;
@@ -92,6 +93,9 @@ bool createUserEnv(EvalState & state, DrvInfos & elems,
             }
         }
     
+        vMeta.attrs->sort();
+        v.attrs->sort();
+        
         /* This is only necessary when installing store paths, e.g.,
            `nix-env -i /nix/store/abcd...-foo'. */
         store->addTempRoot(i->queryOutPath(state));
@@ -118,7 +122,8 @@ bool createUserEnv(EvalState & state, DrvInfos & elems,
     mkString(*state.allocAttr(args, state.sSystem), thisSystem);
     mkString(*state.allocAttr(args, state.symbols.create("manifest")),
         manifestFile, singleton<PathSet>(manifestFile));
-    (*args.attrs)[state.symbols.create("derivations")].value = &manifest;
+    args.attrs->push_back(Attr(state.symbols.create("derivations"), &manifest));
+    args.attrs->sort();
     mkApp(topLevel, envBuilder, args);
         
     /* Evaluate it. */