Improvement in error reporting.

This fix prevents certain situations when an inappropriate form
is reported, in the default unhandled exception handler, as pertaining
to an error.

* eval.c (do_eval): Save and restore the last_form_evaled,
in an exception-unsafe way.  If we successfully evaluate a form or
subform, we can restore the previous one.
(expand): Save and restore last_form_expanded similarly. We don't
need the unwind block and counter.

2 files changed, 24 insertions, 15 deletions

diff --git a/ChangeLog b/ChangeLog
index 1945b2a5..12d4babb 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,17 @@
+2015-04-19  Kaz Kylheku  <kaz@kylheku.com>
+
+	Improvement in error reporting.
+
+	This fix prevents certain situations when an inappropriate form
+	is reported, in the default unhandled exception handler, as pertaining
+	to an error.
+
+	* eval.c (do_eval): Save and restore the last_form_evaled,
+	in an exception-unsafe way.  If we successfully evaluate a form or
+	subform, we can restore the previous one.
+	(expand): Save and restore last_form_expanded similarly. We don't
+	need the unwind block and counter.
+
 2015-04-18  Kaz Kylheku  <kaz@kylheku.com>
 
 	Adding lcons macro.
diff --git a/eval.c b/eval.c
index e8eaa5a7..35b1c2cc 100644
--- a/eval.c
+++ b/eval.c
@@ -1031,8 +1031,10 @@ static val do_eval(val form, val env, val ctx_form,
 
     if (entry) {
       opfun_t fp = coerce(opfun_t, cptr_get(entry));
-      last_form_evaled = form;
-      debug_return (fp(form, env));
+      val ret, lfe_save = last_form_evaled;
+      ret = fp(form, env);
+      last_form_evaled = lfe_save;
+      debug_return (ret);
     } else {
       val fbinding = lookup_fun(env, oper);
       if (!fbinding) {
@@ -1041,9 +1043,12 @@ static val do_eval(val form, val env, val ctx_form,
         abort();
       } else {
         val args = do_eval_args(rest(form), env, form, &lookup_var);
+        val ret, lfe_save = last_form_evaled;
         debug_frame(oper, args, nil, env, nil, nil, nil);
         last_form_evaled = form;
-        debug_return (apply(cdr(fbinding), z(args), form));
+        ret = apply(cdr(fbinding), z(args), form);
+        last_form_evaled = lfe_save;
+        debug_return (ret);
         debug_end;
       }
     }
@@ -3129,21 +3134,11 @@ tail:
 val expand(val form, val menv)
 {
   val ret = nil;
-  static int reentry_count;
-
-  uw_simple_catch_begin;
-
-  reentry_count++;
+  val lfe_save = last_form_expanded;
 
   last_form_expanded = form;
   ret = do_expand(form, menv);
-
-  uw_unwind {
-    if (--reentry_count == 0)
-      last_form_expanded = nil;
-  }
-
-  uw_catch_end;
+  last_form_expanded = lfe_save;
 
   return ret;
 }