GNU bug report logs - #13835
[PATCH] Let reverse! accept arbitrary types as second argument (new_tail)

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From: David Kastrup <dak <at> gnu.org>
To: 13835 <at> debbugs.gnu.org
Cc: David Kastrup <dak <at> gnu.org>
Subject: bug#13835: [PATCH] Let reverse! accept arbitrary types as second argument (new_tail)
Date: Wed, 27 Feb 2013 16:37:21 +0100

There is no reason to restrict the type of the second argument to proper
lists as it is added as last CDR to the list without interpretation.

This allows for stack-depth friendly usage (simplified from an actual
use case that blew up around my ears) like

SCM
my_tree_copy (SCM src)
{
  if (scm_is_pair (src))
    {
      SCM res = SCM_EOL;
      do
        {
          res = scm_cons (my_tree_copy (scm_car (src)), res);
          src = scm_cdr (src);
        }
      while (scm_is_pair (src));
      return scm_reverse_x (res, my_tree_copy (src));
    }
  return src;
}

* libguile/list.c (scm_reverse_x): remove typecheck for 2nd arg
---
 libguile/list.c |    2 --
 1 file changed, 2 deletions(-)

diff --git a/libguile/list.c b/libguile/list.c
index 6c8f8be..d30f9e8 100644
--- a/libguile/list.c
+++ b/libguile/list.c
@@ -377,8 +377,6 @@ SCM_DEFINE (scm_reverse_x, "reverse!", 1, 1, 0,
   SCM_VALIDATE_LIST (1, lst);
   if (SCM_UNBNDP (new_tail))
     new_tail = SCM_EOL;
-  else
-    SCM_VALIDATE_LIST (2, new_tail);
 
   while (!SCM_NULL_OR_NIL_P (lst))
     {
-- 
1.7.10.4

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