Re: append! non-tail recursion

[Kevin Ryde <user42@zip.com.au>]

I ended up with this change,

        * list.c (scm_append_x): Use iterative style, to avoid non-tail
        recursion.

New code:

SCM_DEFINE (scm_append_x, "append!", 0, 0, 1,
            (SCM lists),
            "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"
            "the next list, so no consing is performed.  Return\n"
            "the mutated list.")
#define FUNC_NAME s_scm_append_x
{
  SCM ret, *loc;
  SCM_VALIDATE_REST_ARGUMENT (lists);

  if (SCM_NULLP (lists))
    return SCM_EOL;

  loc = &ret;
  for (;;)
    {
      SCM arg = SCM_CAR (lists);
      *loc = arg;

      lists = SCM_CDR (lists);
      if (SCM_NULLP (lists))
        return ret;

      if (!SCM_NULL_OR_NIL_P (arg))
        {
          SCM_VALIDATE_CONS (SCM_ARG1, arg);
          loc = SCM_CDRLOC (scm_last_pair (arg));
        }
    }
}
#undef FUNC_NAME


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