4 files changed, 19 insertions, 4 deletions
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index acf1fbdc1356..df1600bc1963 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -1032,6 +1032,17 @@ void EvalState::autoCallFunction(Bindings & args, Value & fun, Value & res)
 {
     forceValue(fun);
 
+    if (fun.type == tAttrs) {
+        auto found = fun.attrs->find(sFunctor);
+        if (found != fun.attrs->end()) {
+            forceValue(*found->value);
+            Value * v = allocValue();
+            callFunction(*found->value, fun, *v, noPos);
+            forceValue(*v);
+            return autoCallFunction(args, *v, res);
+        }
+    }
+
     if (fun.type != tLambda || !fun.lambda.fun->matchAttrs) {
         res = fun;
         return;
diff --git a/src/libexpr/local.mk b/src/libexpr/local.mk
index d1b1987fb037..5de9ccc6d011 100644
--- a/src/libexpr/local.mk
+++ b/src/libexpr/local.mk
@@ -10,7 +10,10 @@ libexpr_CXXFLAGS := -Wno-deprecated-register
 
 libexpr_LIBS = libutil libstore libformat
 
-libexpr_LDFLAGS = -ldl
+libexpr_LDFLAGS =
+ifneq ($(OS), FreeBSD)
+ libexpr_LDFLAGS += -ldl
+endif
 
 # The dependency on libgc must be propagated (i.e. meaning that
 # programs/libraries that use libexpr must explicitly pass -lgc),
diff --git a/src/libexpr/nixexpr.cc b/src/libexpr/nixexpr.cc
index 35db52a13acc..5bc8e4202a49 100644
--- a/src/libexpr/nixexpr.cc
+++ b/src/libexpr/nixexpr.cc
@@ -30,8 +30,9 @@ static void showString(std::ostream & str, const string & s)
 
 static void showId(std::ostream & str, const string & s)
 {
-    assert(!s.empty());
-    if (s == "if")
+    if (s.empty())
+        str << "\"\"";
+    else if (s == "if") // FIXME: handle other keywords
         str << '"' << s << '"';
     else {
         char c = s[0];
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 5b9ecc018f0e..cf2d3d278f28 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -1154,7 +1154,7 @@ static void prim_catAttrs(EvalState & state, const Pos & pos, Value * * args, Va
 
 /* Return a set containing the names of the formal arguments expected
    by the function `f'.  The value of each attribute is a Boolean
-   denoting whether has a default value.  For instance,
+   denoting whether the corresponding argument has a default value.  For instance,
 
       functionArgs ({ x, y ? 123}: ...)
    => { x = false; y = true; }