expander: expand arguments after hook processing.

* eval.c (do_expand): Do not expand the arguments of a
function call prior to checking for and dispatching
the expand hook. The expand hook may rewrite the
entire form and the arguments, so that those expansions
are then thrown away. Not only is it wasteful to
calculate them but possibly wrong. A form that is
rewritten by a hook may have strange syntax, such that
the hook itself will get confused if it is unleashed
recursively on the constituent fragments of the syntax.

1 files changed, 16 insertions, 14 deletions

diff --git a/eval.c b/eval.c
index 9cb982b3..7b485e6f 100644
--- a/eval.c
+++ b/eval.c
@@ -5458,20 +5458,7 @@ again:
       val insym = first(form_ex);
       val insym_ex = insym;
       val args = rest(form_ex);
-      val args_ex = expand_forms(args, menv);
-
-      if (sym == setq_s) {
-        syn_check(form, sym, cddr, cdddr);
-
-        {
-          val target = car(args_ex);
-
-          if (!consp(target) || car(target) != var_s) {
-            if (!bindable(target))
-              not_bindable_warning(form, car(args_ex));
-          }
-        }
-      }
+      val args_ex;
 
       if (sym == return_s)
         syn_check(form, sym, identity, cddr);
@@ -5508,6 +5495,21 @@ again:
         }
       }
 
+      args_ex = expand_forms(args, menv);
+
+      if (sym == setq_s) {
+        syn_check(form, sym, cddr, cdddr);
+
+        {
+          val target = car(args_ex);
+
+          if (!consp(target) || car(target) != var_s) {
+            if (!bindable(target))
+              not_bindable_warning(form, car(args_ex));
+          }
+        }
+      }
+
       if (insym_ex == rcons_s &&
           proper_list_p(args_ex) && length(args_ex) == two &&
           constantp_noex(car(args_ex)) &&