Fix mismanaged dyn_env variable.

* eval.c (bindings_helper): In the parallel binding case, only allocate
a new dynamic env when it is needed (because a special variable is
being bound), rather than unconditionally.
Consequently, only modify dyn_env when the dynamic environment actually
needs to be extended.  Constructs that use bindings_helper are only
wrapped in the dynamic environment save/restore form
sys:with-saved-vars if they bind special variables.

2 files changed, 16 insertions, 3 deletions

diff --git a/ChangeLog b/ChangeLog
index 07bacd94..e5d64fb4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,15 @@
+2015-05-25  Kaz Kylheku  <kaz@kylheku.com>
+
+	Fix mismanaged dyn_env variable.
+
+	* eval.c (bindings_helper): In the parallel binding case, only allocate
+	a new dynamic env when it is needed (because a special variable is
+	being bound), rather than unconditionally.
+	Consequently, only modify dyn_env when the dynamic environment actually
+	needs to be extended.  Constructs that use bindings_helper are only
+	wrapped in the dynamic environment save/restore form
+	sys:with-saved-vars if they bind special variables.
+
 2015-05-22  Kaz Kylheku  <kaz@kylheku.com>
 
 	Ligher weight debug instrumentation.
diff --git a/eval.c b/eval.c
index 45962114..53da1188 100644
--- a/eval.c
+++ b/eval.c
@@ -1135,7 +1135,7 @@ static val bindings_helper(val vars, val env, val sequential,
                            val ctx_form)
 {
   val iter;
-  val de = if3(sequential, dyn_env, make_env(nil, nil, dyn_env));
+  val de = if3(sequential, dyn_env, nil);
   val ne = if3(sequential, env, make_env(nil, nil, env));
   list_collect_decl (new_bindings, ptail);
 
@@ -1152,7 +1152,8 @@ static val bindings_helper(val vars, val env, val sequential,
 
     if (var == special_s) {
       val special = car(item);
-      val binding = env_vbind(de, special, value);
+      val binding = env_vbind(de = (de ? de : make_env(nil, nil, dyn_env)),
+                              special, value);
       if (ret_new_bindings)
         ptail = list_collect (ptail, binding);
     } else if (bindable(var)) {
@@ -1167,7 +1168,7 @@ static val bindings_helper(val vars, val env, val sequential,
     }
   }
 
-  if (de != dyn_env)
+  if (de && de != dyn_env)
     dyn_env = de;
   if (env_out)
     *env_out = ne;