* Store attribute sets as a vector instead of a map (i.e. a red-black

  tree).  This saves a lot of memory.  The vector should be sorted so
  that names can be looked up using binary search, but this is not the
  case yet.  (Surprisingly, looking up attributes using linear search
  doesn't have a big impact on performance.)

  Memory consumption for

    $ nix-instantiate /etc/nixos/nixos/tests -A bittorrent.test --readonly-mode

  on x86_64-linux with GC enabled is now 185 MiB (compared to 946
  MiB on the trunk).

7 files changed, 129 insertions, 90 deletions

diff --git a/src/libexpr/attr-path.cc b/src/libexpr/attr-path.cc
index 365b03c0bf60..49c08339ae55 100644
--- a/src/libexpr/attr-path.cc
+++ b/src/libexpr/attr-path.cc
@@ -49,7 +49,7 @@ void findAlongAttrPath(EvalState & state, const string & attrPath,
             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;
+            v = *a->value;
         }
 
         else if (apType == apIndex) {
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index d73f99a156cf..85394b768db6 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -13,7 +13,7 @@
 #include <gc/gc.h>
 #include <gc/gc_cpp.h>
 
-#define NEW (UseGC)
+#define NEW new (UseGC)
 
 #else
 
@@ -30,6 +30,23 @@
 
 
 namespace nix {
+
+
+Bindings::iterator Bindings::find(const Symbol & name)
+{
+    iterator i = begin();
+    for ( ; i != end() && i->name != name; ++i) ;
+    return i;
+}
+
+
+Attr & Bindings::operator [] (const Symbol & name)
+{
+    iterator i = find(name);
+    if (i != end()) return *i;
+    push_back(Attr(name, 0));
+    return back();
+}
     
 
 std::ostream & operator << (std::ostream & str, const Value & v)
@@ -62,7 +79,7 @@ std::ostream & operator << (std::ostream & str, const Value & v)
         typedef std::map<string, Value *> Sorted;
         Sorted sorted;
         foreach (Bindings::iterator, i, *v.attrs)
-            sorted[i->first] = i->second.value;
+            sorted[i->name] = i->value;
         foreach (Sorted::iterator, i, sorted)
             str << i->first << " = " << *i->second << "; ";
         str << "}";
@@ -152,7 +169,7 @@ void EvalState::addConstant(const string & name, Value & v)
     staticBaseEnv.vars[symbols.create(name)] = baseEnvDispl;
     baseEnv.values[baseEnvDispl++] = v2;
     string name2 = string(name, 0, 2) == "__" ? string(name, 2) : name;
-    (*baseEnv.values[0]->attrs)[symbols.create(name2)].value = v2;
+    baseEnv.values[0]->attrs->push_back(Attr(symbols.create(name2), v2));
 }
 
 
@@ -166,7 +183,7 @@ void EvalState::addPrimOp(const string & name,
     v->primOp = NEW PrimOp(primOp, arity, sym);
     staticBaseEnv.vars[sym] = baseEnvDispl;
     baseEnv.values[baseEnvDispl++] = v;
-    (*baseEnv.values[0]->attrs)[symbols.create(name2)].value = v;
+    baseEnv.values[0]->attrs->push_back(Attr(symbols.create(name2), v));
 }
 
 
@@ -277,7 +294,7 @@ Value * EvalState::lookupVar(Env * env, const VarRef & var)
         while (1) {
             Bindings::iterator j = env->values[0]->attrs->find(var.name);
             if (j != env->values[0]->attrs->end())
-                return j->second.value;
+                return j->value;
             if (env->prevWith == 0)
                 throwEvalError("undefined variable `%1%'", var.name);
             for (unsigned int l = env->prevWith; l; --l, env = env->up) ;
@@ -305,9 +322,9 @@ Env & EvalState::allocEnv(unsigned int size)
 
 Value * EvalState::allocAttr(Value & vAttrs, const Symbol & name)
 {
-    Attr & a = (*vAttrs.attrs)[name];
-    a.value = allocValue();
-    return a.value;
+    Value * v = allocValue();
+    vAttrs.attrs->push_back(Attr(name, v));
+    return v;
 }
 
     
@@ -338,8 +355,7 @@ void EvalState::mkThunk_(Value & v, Expr * expr)
 void EvalState::cloneAttrs(Value & src, Value & dst)
 {
     mkAttrs(dst);
-    foreach (Bindings::iterator, i, *src.attrs)
-        (*dst.attrs)[i->first] = i->second;
+    *dst.attrs = *src.attrs;
 }
 
 
@@ -462,21 +478,18 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
         /* The recursive attributes are evaluated in the new
            environment. */
         foreach (Attrs::iterator, i, attrs) {
-            nix::Attr & a = (*v.attrs)[i->first];
-            a.value = state.allocValue();
-            mkThunk(*a.value, env2, i->second.first);
-            env2.values[displ++] = a.value;
-            a.pos = &i->second.second;
+            Value * vAttr = state.allocValue();
+            mkThunk(*vAttr, 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) {
-            nix::Attr & a = (*v.attrs)[i->first.name];
-            Value * v2 = state.lookupVar(&env, i->first);
-            a.value = v2;
-            env2.values[displ++] = v2;
-            a.pos = &i->second;
+            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
@@ -489,12 +502,12 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
            Hence we need __overrides.) */
         Bindings::iterator overrides = v.attrs->find(state.sOverrides);
         if (overrides != v.attrs->end()) {
-            state.forceAttrs(*overrides->second.value);
-            foreach (Bindings::iterator, i, *overrides->second.value->attrs) {
-                nix::Attr & a = (*v.attrs)[i->first];
+            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->first]] = i->second.value;
-                a = i->second;
+                    env2.values[displs[i->name]] = i->value;
+                a = *i;
             }
         }
     }
@@ -565,13 +578,13 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
     if (i == v2.attrs->end())
         throwEvalError("attribute `%1%' missing", name);
     try {            
-        state.forceValue(*i->second.value);
+        state.forceValue(*i->value);
     } catch (Error & e) {
         addErrorPrefix(e, "while evaluating the attribute `%1%' at %2%:\n",
-            name, *i->second.pos);
+            name, *i->pos);
         throw;
     }
-    v = *i->second.value;
+    v = *i->value;
 }
 
 
@@ -676,7 +689,7 @@ void EvalState::callFunction(Value & fun, Value & arg, Value & v)
                 mkThunk(*env2.values[displ++], env2, i->def);
             } else {
                 attrsUsed++;
-                env2.values[displ++] = j->second.value;
+                env2.values[displ++] = j->value;
             }
         }
 
@@ -712,7 +725,7 @@ 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->second;
+            (*actualArgs.attrs)[i->name] = *j;
         else if (!i->def)
             throwTypeError("cannot auto-call a function that has an argument without a default value (`%1%')", i->name);
     }
@@ -801,8 +814,9 @@ void ExprOpUpdate::eval(EvalState & state, Env & env, Value & v)
 
     state.cloneAttrs(v1, v);
 
+    /* !!! fix */
     foreach (Bindings::iterator, i, *v2.attrs)
-        (*v.attrs)[i->first] = i->second;
+        (*v.attrs)[i->name] = *i;
 
     state.nrOpUpdateValuesCopied += v.attrs->size();
 }
@@ -880,7 +894,7 @@ void EvalState::strictForceValue(Value & v)
     
     if (v.type == tAttrs) {
         foreach (Bindings::iterator, i, *v.attrs)
-            strictForceValue(*i->second.value);
+            strictForceValue(*i->value);
     }
     
     else if (v.type == tList) {
@@ -971,7 +985,7 @@ 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";
+    return i != v.attrs->end() && forceStringNoCtx(*i->value) == "derivation";
 }
 
 
@@ -1015,7 +1029,7 @@ string EvalState::coerceToString(Value & v, PathSet & context,
         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);
+        return coerceToString(*i->value, context, coerceMore, copyToStore);
     }
 
     if (coerceMore) {
@@ -1103,7 +1117,7 @@ bool EvalState::eqValues(Value & v1, Value & v2)
             if (v1.attrs->size() != v2.attrs->size()) return false;
             Bindings::iterator i = v1.attrs->begin(), j = v2.attrs->begin();
             for ( ; i != v1.attrs->end(); ++i, ++j)
-                if (i->first != j->first || !eqValues(*i->second.value, *j->second.value))
+                if (i->name != j->name || !eqValues(*i->value, *j->value))
                     return false;
             return true;
         }
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index ec4939442515..2f1b3fa4595e 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -20,13 +20,24 @@ struct Env;
 struct Value;
 struct Attr;
 
+
+/* Attribute sets are represented as a vector of attributes, sorted by
+   symbol (i.e. pointer to the attribute name in the symbol table). */
 #if HAVE_BOEHMGC
-typedef std::map<Symbol, Attr, std::less<Symbol>, gc_allocator<std::pair<const Symbol, Attr> > > Bindings;
+typedef std::vector<Attr, gc_allocator<Attr> > BindingsBase;
 #else
-typedef std::map<Symbol, Attr> Bindings;
+typedef std::vector<Attr> BindingsBase;
 #endif
 
 
+class Bindings : public BindingsBase
+{
+public:
+    iterator find(const Symbol & name);
+    Attr & operator [] (const Symbol & name);
+};
+
+
 typedef enum {
     tInt = 1,
     tBool,
@@ -125,8 +136,11 @@ struct Env
 
 struct Attr
 {
+    Symbol name;
     Value * value;
     Pos * pos;
+    Attr(Symbol name, Value * value, Pos * pos = &noPos)
+        : name(name), value(value), pos(pos) { };
     Attr() : pos(&noPos) { };
 };
 
diff --git a/src/libexpr/get-drvs.cc b/src/libexpr/get-drvs.cc
index 63106b87b5af..312c2cd405e6 100644
--- a/src/libexpr/get-drvs.cc
+++ b/src/libexpr/get-drvs.cc
@@ -10,7 +10,7 @@ string DrvInfo::queryDrvPath(EvalState & state) const
     if (drvPath == "" && attrs) {
         Bindings::iterator i = attrs->find(state.sDrvPath);
         PathSet context;
-        (string &) drvPath = i != attrs->end() ? state.coerceToPath(*i->second.value, context) : "";
+        (string &) drvPath = i != attrs->end() ? state.coerceToPath(*i->value, context) : "";
     }
     return drvPath;
 }
@@ -21,7 +21,7 @@ string DrvInfo::queryOutPath(EvalState & state) const
     if (outPath == "" && attrs) {
         Bindings::iterator i = attrs->find(state.sOutPath);
         PathSet context;
-        (string &) outPath = i != attrs->end() ? state.coerceToPath(*i->second.value, context) : "";
+        (string &) outPath = i != attrs->end() ? state.coerceToPath(*i->value, context) : "";
     }
     return outPath;
 }
@@ -36,23 +36,23 @@ MetaInfo DrvInfo::queryMetaInfo(EvalState & state) const
     Bindings::iterator a = attrs->find(state.sMeta);
     if (a == attrs->end()) return meta; /* fine, empty meta information */
 
-    state.forceAttrs(*a->second.value);
+    state.forceAttrs(*a->value);
 
-    foreach (Bindings::iterator, i, *a->second.value->attrs) {
+    foreach (Bindings::iterator, i, *a->value->attrs) {
         MetaValue value;
-        state.forceValue(*i->second.value);
-        if (i->second.value->type == tString) {
+        state.forceValue(*i->value);
+        if (i->value->type == tString) {
             value.type = MetaValue::tpString;
-            value.stringValue = i->second.value->string.s;
-        } else if (i->second.value->type == tInt) {
+            value.stringValue = i->value->string.s;
+        } else if (i->value->type == tInt) {
             value.type = MetaValue::tpInt;
-            value.intValue = i->second.value->integer;
-        } else if (i->second.value->type == tList) {
+            value.intValue = i->value->integer;
+        } else if (i->value->type == tList) {
             value.type = MetaValue::tpStrings;
-            for (unsigned int j = 0; j < i->second.value->list.length; ++j)
-                value.stringValues.push_back(state.forceStringNoCtx(*i->second.value->list.elems[j]));
+            for (unsigned int j = 0; j < i->value->list.length; ++j)
+                value.stringValues.push_back(state.forceStringNoCtx(*i->value->list.elems[j]));
         } else continue;
-        ((MetaInfo &) meta)[i->first] = value;
+        ((MetaInfo &) meta)[i->name] = value;
     }
 
     return meta;
@@ -99,13 +99,13 @@ static bool getDerivation(EvalState & state, Value & v,
         Bindings::iterator i = v.attrs->find(state.sName);
         /* !!! We really would like to have a decent back trace here. */
         if (i == v.attrs->end()) throw TypeError("derivation name missing");
-        drv.name = state.forceStringNoCtx(*i->second.value);
+        drv.name = state.forceStringNoCtx(*i->value);
 
         Bindings::iterator i2 = v.attrs->find(state.sSystem);
         if (i2 == v.attrs->end())
             drv.system = "unknown";
         else
-            drv.system = state.forceStringNoCtx(*i2->second.value);
+            drv.system = state.forceStringNoCtx(*i2->value);
 
         drv.attrs = v.attrs;
 
@@ -163,7 +163,7 @@ static void getDerivations(EvalState & state, Value & vIn,
         typedef std::map<string, Symbol> SortedSymbols;
         SortedSymbols attrs;
         foreach (Bindings::iterator, i, *v.attrs)
-            attrs.insert(std::pair<string, Symbol>(i->first, i->first));
+            attrs.insert(std::pair<string, Symbol>(i->name, i->name));
 
         foreach (SortedSymbols::iterator, i, attrs) {
             startNest(nest, lvlDebug, format("evaluating attribute `%1%'") % i->first);
@@ -178,7 +178,7 @@ static void getDerivations(EvalState & state, Value & vIn,
                    attribute. */
                 if (v2.type == tAttrs) {
                     Bindings::iterator j = v2.attrs->find(state.symbols.create("recurseForDerivations"));
-                    if (j != v2.attrs->end() && state.forceBool(*j->second.value))
+                    if (j != v2.attrs->end() && state.forceBool(*j->value))
                         getDerivations(state, v2, pathPrefix2, autoArgs, drvs, done);
                 }
             }
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 01cbf7a7c21a..20b8395088d7 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -119,18 +119,18 @@ static void prim_genericClosure(EvalState & state, Value * * args, Value & v)
         args[0]->attrs->find(state.symbols.create("startSet"));
     if (startSet == args[0]->attrs->end())
         throw EvalError("attribute `startSet' required");
-    state.forceList(*startSet->second.value);
+    state.forceList(*startSet->value);
 
     list<Value *> workSet;
-    for (unsigned int n = 0; n < startSet->second.value->list.length; ++n)
-        workSet.push_back(startSet->second.value->list.elems[n]);
+    for (unsigned int n = 0; n < startSet->value->list.length; ++n)
+        workSet.push_back(startSet->value->list.elems[n]);
 
     /* Get the operator. */
     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);
+    state.forceValue(*op->value);
 
     /* Construct the closure by applying the operator to element of
        `workSet', adding the result to `workSet', continuing until
@@ -147,15 +147,15 @@ static void prim_genericClosure(EvalState & state, Value * * args, Value & v)
             e->attrs->find(state.symbols.create("key"));
         if (key == e->attrs->end())
             throw EvalError("attribute `key' required");
-        state.forceValue(*key->second.value);
+        state.forceValue(*key->value);
 
-        if (doneKeys.find(*key->second.value) != doneKeys.end()) continue;
-        doneKeys.insert(*key->second.value);
+        if (doneKeys.find(*key->value) != doneKeys.end()) continue;
+        doneKeys.insert(*key->value);
         res.push_back(*e);
         
         /* Call the `operator' function with `e' as argument. */
         Value call;
-        mkApp(call, *op->second.value, *e);
+        mkApp(call, *op->value, *e);
         state.forceList(call);
 
         /* Add the values returned by the operator to the work set. */
@@ -322,9 +322,9 @@ static void prim_derivationStrict(EvalState & state, Value * * args, Value & v)
     if (attr == args[0]->attrs->end())
         throw EvalError("required attribute `name' missing");
     string drvName;
-    Pos & posDrvName(*attr->second.pos);
+    Pos & posDrvName(*attr->pos);
     try {        
-        drvName = state.forceStringNoCtx(*attr->second.value);
+        drvName = state.forceStringNoCtx(*attr->value);
     } catch (Error & e) {
         e.addPrefix(format("while evaluating the derivation attribute `name' at %1%:\n") % posDrvName);
         throw;
@@ -339,7 +339,7 @@ static void prim_derivationStrict(EvalState & state, Value * * args, Value & v)
     bool outputHashRecursive = false;
 
     foreach (Bindings::iterator, i, *args[0]->attrs) {
-        string key = i->first;
+        string key = i->name;
         startNest(nest, lvlVomit, format("processing attribute `%1%'") % key);
 
         try {
@@ -347,9 +347,9 @@ static void prim_derivationStrict(EvalState & state, Value * * args, Value & v)
             /* The `args' attribute is special: it supplies the
                command-line arguments to the builder. */
             if (key == "args") {
-                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);
+                state.forceList(*i->value);
+                for (unsigned int n = 0; n < i->value->list.length; ++n) {
+                    string s = state.coerceToString(*i->value->list.elems[n], context, true);
                     drv.args.push_back(s);
                 }
             }
@@ -357,11 +357,11 @@ static void prim_derivationStrict(EvalState & state, Value * * args, Value & v)
             /* All other attributes are passed to the builder through
                the environment. */
             else {
-                string s = state.coerceToString(*i->second.value, context, true);
+                string s = state.coerceToString(*i->value, context, true);
                 drv.env[key] = s;
                 if (key == "builder") drv.builder = s;
-                else if (i->first == state.sSystem) drv.platform = s;
-                else if (i->first == state.sName) drvName = s;
+                else if (i->name == state.sSystem) drv.platform = s;
+                else if (i->name == state.sName) drvName = s;
                 else if (key == "outputHash") outputHash = s;
                 else if (key == "outputHashAlgo") outputHashAlgo = s;
                 else if (key == "outputHashMode") {
@@ -373,7 +373,7 @@ static void prim_derivationStrict(EvalState & state, Value * * args, Value & v)
 
         } catch (Error & e) {
             e.addPrefix(format("while evaluating the derivation attribute `%1%' at %2%:\n")
-                % key % *i->second.pos);
+                % key % *i->pos);
             e.addPrefix(format("while instantiating the derivation named `%1%' at %2%:\n")
                 % drvName % posDrvName);
             throw;
@@ -690,7 +690,7 @@ static void prim_attrNames(EvalState & state, Value * * args, Value & v)
 
     StringSet names;
     foreach (Bindings::iterator, i, *args[0]->attrs)
-        names.insert(i->first);
+        names.insert(i->name);
 
     unsigned int n = 0;
     foreach (StringSet::iterator, i, names)
@@ -708,8 +708,8 @@ static void prim_getAttr(EvalState & state, Value * * args, Value & v)
     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;
+    state.forceValue(*i->value);
+    v = *i->value;
 }
 
 
@@ -735,11 +735,18 @@ static void prim_removeAttrs(EvalState & state, Value * * args, Value & v)
     state.forceAttrs(*args[0]);
     state.forceList(*args[1]);
 
-    state.cloneAttrs(*args[0], v);
-
+    /* Get the attribute names to be removed. */
+    std::set<Symbol> names;
     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));
+        names.insert(state.symbols.create(args[1]->list.elems[i]->string.s));
+    }
+
+    /* Copy all attributes not in that set. */
+    state.mkAttrs(v);
+    foreach (Bindings::iterator, i, *args[0]->attrs) {
+        if (names.find(i->name) == names.end())
+            v.attrs->push_back(*i);
     }
 }
 
@@ -761,13 +768,15 @@ static void prim_listToAttrs(EvalState & state, Value * * args, Value & v)
         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);
+        string name = state.forceStringNoCtx(*j->value);
         
         Bindings::iterator j2 = v2.attrs->find(state.symbols.create("value"));
         if (j2 == v2.attrs->end())
             throw TypeError("`value' attribute missing in a call to `listToAttrs'");
 
-        (*v.attrs)[state.symbols.create(name)] = j2->second;
+        Attr & a = (*v.attrs)[state.symbols.create(name)];
+        a.value = j2->value;
+        a.pos = j2->pos;
     }
 }
 
@@ -783,9 +792,9 @@ static void prim_intersectAttrs(EvalState & state, Value * * args, Value & v)
     state.mkAttrs(v);
 
     foreach (Bindings::iterator, i, *args[0]->attrs) {
-        Bindings::iterator j = args[1]->attrs->find(i->first);
+        Bindings::iterator j = args[1]->attrs->find(i->name);
         if (j != args[1]->attrs->end())
-            (*v.attrs)[j->first] = j->second;
+            v.attrs->push_back(*j);
     }
 }
 
diff --git a/src/libexpr/symbol-table.hh b/src/libexpr/symbol-table.hh
index 20ebe5fedbf6..976117a20a46 100644
--- a/src/libexpr/symbol-table.hh
+++ b/src/libexpr/symbol-table.hh
@@ -28,6 +28,8 @@ private:
     friend class SymbolTable;
 
 public:
+    Symbol() : s(0) { };
+    
     bool operator == (const Symbol & s2) const
     {
         return s == s2.s;
diff --git a/src/libexpr/value-to-xml.cc b/src/libexpr/value-to-xml.cc
index 1bb200fb858b..4f9b62d5f15e 100644
--- a/src/libexpr/value-to-xml.cc
+++ b/src/libexpr/value-to-xml.cc
@@ -34,7 +34,7 @@ static void showAttrs(EvalState & state, bool strict, bool location,
     StringSet names;
     
     foreach (Bindings::iterator, i, attrs)
-        names.insert(i->first);
+        names.insert(i->name);
     
     foreach (StringSet::iterator, i, names) {
         Attr & a(attrs[state.symbols.create(*i)]);
@@ -90,16 +90,16 @@ static void printValueAsXML(EvalState & state, bool strict, bool location,
                 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;
+                    if (strict) state.forceValue(*a->value);
+                    if (a->value->type == tString)
+                        xmlAttrs["drvPath"] = drvPath = a->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;
+                    if (strict) state.forceValue(*a->value);
+                    if (a->value->type == tString)
+                        xmlAttrs["outPath"] = a->value->string.s;
                 }
 
                 XMLOpenElement _(doc, "derivation", xmlAttrs);