degenerate let forms

[bpt/guile.git] / libguile / list.c

diff --git a/libguile/list.c b/libguile/list.c
index 8297b17..41cc937 100644 (file)
--- a/libguile/list.c
+++ b/libguile/list.c
@@ -267,7 +267,7 @@ SCM_DEFINE (scm_append, "append", 0, 0, 1,
 
 
 SCM_DEFINE (scm_append_x, "append!", 0, 0, 1, 
-            (SCM lists),
+            (SCM args),
            "A destructive version of @code{append} (@pxref{Pairs and\n"
            "Lists,,,r5rs, The Revised^5 Report on Scheme}).  The cdr field\n"
            "of each list's final pair is changed to point to the head of\n"
@@ -276,26 +276,29 @@ SCM_DEFINE (scm_append_x, "append!", 0, 0, 1,
 #define FUNC_NAME s_scm_append_x
 {
   SCM ret, *loc;
-  SCM_VALIDATE_REST_ARGUMENT (lists);
+  int argnum = 1;
+  SCM_VALIDATE_REST_ARGUMENT (args);
 
-  if (scm_is_null (lists))
+  if (scm_is_null (args))
     return SCM_EOL;
 
   loc = &ret;
   for (;;)
     {
-      SCM arg = SCM_CAR (lists);
+      SCM arg = SCM_CAR (args);
       *loc = arg;
 
-      lists = SCM_CDR (lists);
-      if (scm_is_null (lists))
+      args = SCM_CDR (args);
+      if (scm_is_null (args))
         return ret;
 
       if (!SCM_NULL_OR_NIL_P (arg))
         {
-          SCM_VALIDATE_CONS (SCM_ARG1, arg);
+          SCM_VALIDATE_CONS (argnum, arg);
           loc = SCM_CDRLOC (scm_last_pair (arg));
+          SCM_VALIDATE_NULL_OR_NIL (argnum, *loc);
         }
+      argnum++;
     }
 }
 #undef FUNC_NAME
@@ -371,20 +374,49 @@ SCM_DEFINE (scm_reverse_x, "reverse!", 1, 1, 0,
            "@code{reverse!}")
 #define FUNC_NAME s_scm_reverse_x
 {
-  SCM_VALIDATE_LIST (1, lst);
+  SCM old_lst = lst;
+  SCM tail = SCM_BOOL_F;
+
   if (SCM_UNBNDP (new_tail))
     new_tail = SCM_EOL;
-  else
-    SCM_VALIDATE_LIST (2, new_tail);
 
-  while (!SCM_NULL_OR_NIL_P (lst))
+  if (SCM_NULL_OR_NIL_P (lst))
+    return new_tail;
+
+  /* SCM_VALIDATE_LIST would run through the whole list to make sure it
+     is not eventually circular.  In contrast to most list operations,
+     reverse! cannot get stuck in an infinite loop but arrives back at
+     the start when given an eventually or fully circular list.  Because
+     of that, we can save the cost of an upfront proper list check at
+     the price of having to do a double reversal in the error case.
+  */
+
+  while (scm_is_pair (lst))
     {
       SCM old_tail = SCM_CDR (lst);
-      SCM_SETCDR (lst, new_tail);
-      new_tail = lst;
+      SCM_SETCDR (lst, tail);
+      tail = lst;
       lst = old_tail;
     }
-  return new_tail;
+
+  if (SCM_LIKELY (SCM_NULL_OR_NIL_P (lst)))
+    {
+      SCM_SETCDR (old_lst, new_tail);
+      return tail;
+    }
+
+  /* We did not start with a proper list.  Undo the reversal. */
+
+  while (scm_is_pair (tail))
+    {
+      SCM old_tail = SCM_CDR (tail);
+      SCM_SETCDR (tail, lst);
+      lst = tail;
+      tail = old_tail;
+    }
+
+  SCM_WRONG_TYPE_ARG (1, lst);
+  return lst;
 }
 #undef FUNC_NAME