3 files changed, 35 insertions, 10 deletions
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index d70ac9f76a23..384d87a269ee 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -29,6 +29,19 @@ static Expr substArgs(Expr body, ATermList formals, Expr arg)
     ATermMap subs(ATgetLength(formals) * 2);
     Expr undefined = makeUndefined();
 
+    /* ({x ? E1; y ? E2, z}: E3) {x = E4; z = E5;}
+
+       => let {x = E4; y = E2; z = E5; body = E3; }
+
+       => subst(E3, s)
+          s = {
+            R = rec {x = E4; y = E2; z = E5}
+            x -> R.x
+            y -> R.y
+            z -> R.z
+          }
+    */
+    
     /* Get the formal arguments. */
     for (ATermIterator i(formals); i; ++i) {
         Expr name, def;
@@ -278,7 +291,7 @@ Expr evalExpr2(EvalState & state, Expr e)
     if (matchVar(e, name)) {
         ATerm primOp = state.primOps.get(name);
         if (!primOp)
-            throw Error(format("impossible: undefined variable `%1%'") % name);
+            throw Error(format("impossible: undefined variable `%1%'") % aterm2String(name));
         int arity;
         ATermBlob fun;
         if (!matchPrimOpDef(primOp, arity, fun)) abort();
@@ -509,9 +522,16 @@ Expr evalFile(EvalState & state, const Path & path)
 }
 
 
+/* Yes, this is a really bad idea... */
+extern "C" {
+    unsigned long AT_calcAllocatedSize();
+}
+
 void printEvalStats(EvalState & state)
 {
-    debug(format("evaluated %1% expressions, %2% cache hits, %3%%% efficiency")
+    printMsg(lvlInfo,
+        format("evaluated %1% expressions, %2% cache hits, %3%%% efficiency, used %4% ATerm bytes")
         % state.nrEvaluated % state.nrCached
-        % ((float) state.nrCached / (float) state.nrEvaluated * 100));
+        % ((float) state.nrCached / (float) state.nrEvaluated * 100)
+        % AT_calcAllocatedSize());
 }
diff --git a/src/libexpr/get-drvs.cc b/src/libexpr/get-drvs.cc
index b101f2da30d1..bc2302a0b2fb 100644
--- a/src/libexpr/get-drvs.cc
+++ b/src/libexpr/get-drvs.cc
@@ -177,7 +177,7 @@ static void getDerivations(EvalState & state, Expr e,
                     format("evaluating attribute `%1%'") % aterm2String(*i));
                 if (getDerivation(state, drvMap.get(*i), drvs, doneExprs)) {
                     /* If the value of this attribute is itself an
-                       attribute self, should we recurse into it?
+                       attribute set, should we recurse into it?
                        => Only if it has a `recurseForDerivations = true'
                        attribute. */
                     ATermList es;
diff --git a/src/libexpr/nixexpr.cc b/src/libexpr/nixexpr.cc
index aee57acb116e..05c1ee45ceea 100644
--- a/src/libexpr/nixexpr.cc
+++ b/src/libexpr/nixexpr.cc
@@ -226,6 +226,8 @@ Expr substitute(const ATermMap & subs, Expr e)
 {
     checkInterrupt();
 
+    //if (subs.size() == 0) return e;
+
     ATerm name, pos, e2;
 
     /* As an optimisation, don't substitute in subterms known to be
@@ -255,7 +257,7 @@ Expr substitute(const ATermMap & subs, Expr e)
             subs2.remove(name);
         }
         return makeFunction(
-            (ATermList) substitute(subs, (ATerm) formals),
+            (ATermList) substitute(subs2, (ATerm) formals),
             substitute(subs2, body), pos);
     }
 
@@ -327,13 +329,16 @@ static void checkVarDefs2(set<Expr> & done, const ATermMap & defs, Expr e)
         ATermMap defs2(defs);
         for (ATermIterator i(formals); i; ++i) {
             Expr deflt;
-            if (!matchNoDefFormal(*i, name))
-                if (matchDefFormal(*i, name, deflt))
-                    checkVarDefs2(done, defs, deflt);
-                else
-                    abort();
+            if (!matchNoDefFormal(*i, name) &&
+                !matchDefFormal(*i, name, deflt))
+                abort();
             defs2.set(name, (ATerm) ATempty);
         }
+        for (ATermIterator i(formals); i; ++i) {
+            Expr deflt;
+            if (matchDefFormal(*i, name, deflt))
+                checkVarDefs2(done, defs2, deflt);
+        }
         checkVarDefs2(done, defs2, body);
     }