guile/srfi/srfi-1.c

/* srfi-1.c --- SRFI-1 procedures for Guile
 *
 * 	Copyright (C) 1995, 1996, 1997, 2000, 2001, 2002, 2003, 2005, 2006, 2008, 2009, 2010
 *   	Free Software Foundation, Inc.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation; either version 3 of
 * the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301 USA
 */

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#include <libguile.h>

#include "srfi-1.h"

/* The intent of this file was to gradually replace those Scheme
 * procedures in srfi-1.scm that extend core primitive procedures,
 * so that using srfi-1 won't have performance penalties.
 *
 * However, we now prefer to write these procedures in Scheme, let the compiler
 * optimize them, and have the VM execute them efficiently.
 */


/* The `(srfi srfi-1)' module.  */
static SCM srfi1_module = SCM_BOOL_F;

/* Cache variable NAME in C variable VAR.  */
#define CACHE_VAR(var, name)						\
  static SCM var = SCM_BOOL_F;						\
  if (scm_is_false (var))						\
    {									\
      if (SCM_UNLIKELY (scm_is_false (srfi1_module)))			\
	srfi1_module = scm_c_resolve_module ("srfi srfi-1");		\
									\
      var = scm_module_variable (srfi1_module,				\
                                 scm_from_locale_symbol (name));	\
      if (SCM_UNLIKELY (scm_is_false (var)))				\
        abort ();							\
									\
      var = SCM_VARIABLE_REF (var);					\
    }

static long
srfi1_ilength (SCM sx)
{
  long i = 0;
  SCM tortoise = sx;
  SCM hare = sx;

  do {
    if (SCM_NULL_OR_NIL_P(hare)) return i;
    if (!scm_is_pair (hare)) return -2;
    hare = SCM_CDR(hare);
    i++;
    if (SCM_NULL_OR_NIL_P(hare)) return i;
    if (!scm_is_pair (hare)) return -2;
    hare = SCM_CDR(hare);
    i++;
    /* For every two steps the hare takes, the tortoise takes one.  */
    tortoise = SCM_CDR(tortoise);
  }
  while (! scm_is_eq (hare, tortoise));

  /* If the tortoise ever catches the hare, then the list must contain
     a cycle.  */
  return -1;
}

static SCM
equal_trampoline (SCM proc, SCM arg1, SCM arg2)
{
  return scm_equal_p (arg1, arg2);
}

/* list_copy_part() copies the first COUNT cells of LST, puts the result at
   *dst, and returns the SCM_CDRLOC of the last cell in that new list.

   This function is designed to be careful about LST possibly having changed
   in between the caller deciding what to copy, and the copy actually being
   done here.  The COUNT ensures we terminate if LST has become circular,
   SCM_VALIDATE_CONS guards against a cdr in the list changed to some
   non-pair object.  */

#include <stdio.h>
static SCM *
list_copy_part (SCM lst, int count, SCM *dst)
#define FUNC_NAME "list_copy_part"
{
  SCM c;
  for ( ; count > 0; count--)
    {
      SCM_VALIDATE_CONS (SCM_ARGn, lst);
      c = scm_cons (SCM_CAR (lst), SCM_EOL);
      *dst = c;
      dst = SCM_CDRLOC (c);
      lst = SCM_CDR (lst);
    }
  return dst;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_alist_copy, "alist-copy", 1, 0, 0,
            (SCM alist),
	    "Return a copy of @var{alist}, copying both the pairs comprising\n"
	    "the list and those making the associations.")
#define FUNC_NAME s_scm_srfi1_alist_copy
{
  SCM  ret, *p, elem, c;

  /* ret is the list to return.  p is where to append to it, initially &ret
     then SCM_CDRLOC of the last pair.  */
  ret = SCM_EOL;
  p = &ret;

  for ( ; scm_is_pair (alist); alist = SCM_CDR (alist))
    {
      elem = SCM_CAR (alist);

      /* each element of alist must be a pair */
      SCM_ASSERT_TYPE (scm_is_pair (elem), alist, SCM_ARG1, FUNC_NAME,
                       "association list");

      c = scm_cons (scm_cons (SCM_CAR (elem), SCM_CDR (elem)), SCM_EOL);
      *p = c;
      p = SCM_CDRLOC (c);
    }

  /* alist must be a proper list */
  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (alist), alist, SCM_ARG1, FUNC_NAME,
                   "association list");
  return ret;
}
#undef FUNC_NAME



SCM_DEFINE (scm_srfi1_append_reverse, "append-reverse", 2, 0, 0,
            (SCM revhead, SCM tail),
	    "Reverse @var{rev-head}, append @var{tail} to it, and return the\n"
	    "result.  This is equivalent to @code{(append (reverse\n"
	    "@var{rev-head}) @var{tail})}, but its implementation is more\n"
	    "efficient.\n"
	    "\n"
	    "@example\n"
	    "(append-reverse '(1 2 3) '(4 5 6)) @result{} (3 2 1 4 5 6)\n"
	    "@end example")
#define FUNC_NAME s_scm_srfi1_append_reverse
{
  while (scm_is_pair (revhead))
    {
      /* copy first element of revhead onto front of tail */
      tail = scm_cons (SCM_CAR (revhead), tail);
      revhead = SCM_CDR (revhead);
    }
  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (revhead), revhead, SCM_ARG1, FUNC_NAME,
                   "list");
  return tail;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_append_reverse_x, "append-reverse!", 2, 0, 0,
            (SCM revhead, SCM tail),
	    "Reverse @var{rev-head}, append @var{tail} to it, and return the\n"
	    "result.  This is equivalent to @code{(append! (reverse!\n"
	    "@var{rev-head}) @var{tail})}, but its implementation is more\n"
	    "efficient.\n"
	    "\n"
	    "@example\n"
	    "(append-reverse! (list 1 2 3) '(4 5 6)) @result{} (3 2 1 4 5 6)\n"
	    "@end example\n"
	    "\n"
	    "@var{rev-head} may be modified in order to produce the result.")
#define FUNC_NAME s_scm_srfi1_append_reverse_x
{
  SCM newtail;

  while (scm_is_pair (revhead))
    {
      /* take the first cons cell from revhead */
      newtail = revhead;
      revhead = SCM_CDR (revhead);

      /* make it the new start of tail, appending the previous */
      SCM_SETCDR (newtail, tail);
      tail = newtail;
    }
  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (revhead), revhead, SCM_ARG1, FUNC_NAME,
                   "list");
  return tail;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_break, "break", 2, 0, 0,
            (SCM pred, SCM lst),
	    "Return two values, the longest initial prefix of @var{lst}\n"
	    "whose elements all fail the predicate @var{pred}, and the\n"
	    "remainder of @var{lst}.\n"
	    "\n"
	    "Note that the name @code{break} conflicts with the @code{break}\n"
	    "binding established by @code{while}.  Applications wanting to\n"
	    "use @code{break} from within a @code{while} loop will need to\n"
	    "make a new define under a different name.")
#define FUNC_NAME s_scm_srfi1_break
{
  SCM ret, *p;

  SCM_ASSERT (scm_is_true (scm_procedure_p (pred)), pred, SCM_ARG1, FUNC_NAME);

  ret = SCM_EOL;
  p = &ret;
  for ( ; scm_is_pair (lst); lst = SCM_CDR (lst))
    {
      SCM elem = SCM_CAR (lst);
      if (scm_is_true (scm_call_1 (pred, elem)))
        goto done;

      /* want this elem, tack it onto the end of ret */
      *p = scm_cons (elem, SCM_EOL);
      p = SCM_CDRLOC (*p);
    }
  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (lst), lst, SCM_ARG2, FUNC_NAME, "list");

 done:
  return scm_values (scm_list_2 (ret, lst));
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_break_x, "break!", 2, 0, 0,
            (SCM pred, SCM lst),
	    "Return two values, the longest initial prefix of @var{lst}\n"
	    "whose elements all fail the predicate @var{pred}, and the\n"
	    "remainder of @var{lst}.  @var{lst} may be modified to form the\n"
	    "return.")
#define FUNC_NAME s_scm_srfi1_break_x
{
  SCM upto, *p;

  SCM_ASSERT (scm_is_true (scm_procedure_p (pred)), pred, SCM_ARG1, FUNC_NAME);

  p = &lst;
  for (upto = lst; scm_is_pair (upto); upto = SCM_CDR (upto))
    {
      if (scm_is_true (scm_call_1 (pred, SCM_CAR (upto))))
        goto done;

      /* want this element */
      p = SCM_CDRLOC (upto);
    }
  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (upto), lst, SCM_ARG2, FUNC_NAME, "list");

 done:
  *p = SCM_EOL;
  return scm_values (scm_list_2 (lst, upto));
}
#undef FUNC_NAME


SCM
scm_srfi1_car_plus_cdr (SCM pair)
{
  CACHE_VAR (car_plus_cdr, "car+cdr");
  return scm_call_1 (car_plus_cdr, pair);
}

SCM_DEFINE (scm_srfi1_concatenate, "concatenate", 1, 0, 0,
            (SCM lstlst),
	    "Construct a list by appending all lists in @var{lstlst}.\n"
	    "\n"
	    "@code{concatenate} is the same as @code{(apply append\n"
	    "@var{lstlst})}.  It exists because some Scheme implementations\n"
	    "have a limit on the number of arguments a function takes, which\n"
	    "the @code{apply} might exceed.  In Guile there is no such\n"
	    "limit.")
#define FUNC_NAME s_scm_srfi1_concatenate
{
  SCM_VALIDATE_LIST (SCM_ARG1, lstlst);
  return scm_append (lstlst);
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_concatenate_x, "concatenate!", 1, 0, 0,
            (SCM lstlst),
	    "Construct a list by appending all lists in @var{lstlst}.  Those\n"
	    "lists may be modified to produce the result.\n"
	    "\n"
	    "@code{concatenate!} is the same as @code{(apply append!\n"
	    "@var{lstlst})}.  It exists because some Scheme implementations\n"
	    "have a limit on the number of arguments a function takes, which\n"
	    "the @code{apply} might exceed.  In Guile there is no such\n"
	    "limit.")
#define FUNC_NAME s_scm_srfi1_concatenate
{
  SCM_VALIDATE_LIST (SCM_ARG1, lstlst);
  return scm_append_x (lstlst);
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_count, "count", 2, 0, 1,
            (SCM pred, SCM list1, SCM rest),
	    "Return a count of the number of times @var{pred} returns true\n"
	    "when called on elements from the given lists.\n"
	    "\n"
	    "@var{pred} is called with @var{N} parameters @code{(@var{pred}\n"
	    "@var{elem1} @dots{} @var{elemN})}, each element being from the\n"
	    "corresponding @var{list1} @dots{} @var{lstN}.  The first call is\n"
	    "with the first element of each list, the second with the second\n"
	    "element from each, and so on.\n"
	    "\n"
	    "Counting stops when the end of the shortest list is reached.\n"
	    "At least one list must be non-circular.")
#define FUNC_NAME s_scm_srfi1_count
{
  long  count;
  SCM   lst;
  int   argnum;
  SCM_VALIDATE_REST_ARGUMENT (rest);

  count = 0;

  if (scm_is_null (rest))
    {
      /* one list */
      SCM_ASSERT (scm_is_true (scm_procedure_p (pred)), pred, SCM_ARG1, FUNC_NAME);

      for ( ; scm_is_pair (list1); list1 = SCM_CDR (list1))
        count += scm_is_true (scm_call_1 (pred, SCM_CAR (list1)));

      /* check below that list1 is a proper list, and done */
    end_list1:
      lst = list1;
      argnum = 2;
    }
  else if (scm_is_pair (rest) && scm_is_null (SCM_CDR (rest)))
    {
      /* two lists */
      SCM list2;

      SCM_ASSERT (scm_is_true (scm_procedure_p (pred)), pred, SCM_ARG1, FUNC_NAME);

      list2 = SCM_CAR (rest);
      for (;;)
        {
          if (! scm_is_pair (list1))
            goto end_list1;
          if (! scm_is_pair (list2))
            {
              lst = list2;
              argnum = 3;
              break;
            }
          count += scm_is_true (scm_call_2
				(pred, SCM_CAR (list1), SCM_CAR (list2)));
          list1 = SCM_CDR (list1);
          list2 = SCM_CDR (list2);
        }
    }
  else
    {
      /* three or more lists */
      SCM  vec, args, a;
      size_t  len, i;

      /* vec is the list arguments */
      vec = scm_vector (scm_cons (list1, rest));
      len = SCM_SIMPLE_VECTOR_LENGTH (vec);

      /* args is the argument list to pass to pred, same length as vec,
         re-used for each call */
      args = scm_make_list (SCM_I_MAKINUM (len), SCM_UNDEFINED);

      for (;;)
        {
          /* first elem of each list in vec into args, and step those
             vec entries onto their next element */
          for (i = 0, a = args, argnum = 2;
               i < len;
               i++, a = SCM_CDR (a), argnum++)
            {
              lst = SCM_SIMPLE_VECTOR_REF (vec, i);  /* list argument */
              if (! scm_is_pair (lst))
                goto check_lst_and_done;
              SCM_SETCAR (a, SCM_CAR (lst));  /* arg for pred */
              SCM_SIMPLE_VECTOR_SET (vec, i, SCM_CDR (lst));  /* rest of lst */
            }

          count += scm_is_true (scm_apply (pred, args, SCM_EOL));
        }
    }

 check_lst_and_done:
  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (lst), lst, argnum, FUNC_NAME, "list");
  return scm_from_long (count);
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_delete, "delete", 2, 1, 0,
            (SCM x, SCM lst, SCM pred),
	    "Return a list containing the elements of @var{lst} but with\n"
	    "those equal to @var{x} deleted.  The returned elements will be\n"
	    "in the same order as they were in @var{lst}.\n"
	    "\n"
	    "Equality is determined by @var{pred}, or @code{equal?} if not\n"
	    "given.  An equality call is made just once for each element,\n"
	    "but the order in which the calls are made on the elements is\n"
	    "unspecified.\n"
	    "\n"
	    "The equality calls are always @code{(pred x elem)}, ie.@: the\n"
	    "given @var{x} is first.  This means for instance elements\n"
	    "greater than 5 can be deleted with @code{(delete 5 lst <)}.\n"
	    "\n"
	    "@var{lst} is not modified, but the returned list might share a\n"
	    "common tail with @var{lst}.")
#define FUNC_NAME s_scm_srfi1_delete
{
  SCM  ret, *p, keeplst;
  int  count;

  if (SCM_UNBNDP (pred))
    return scm_delete (x, lst);

  SCM_ASSERT (scm_is_true (scm_procedure_p (pred)), pred, SCM_ARG3, FUNC_NAME);

  /* ret is the return list being constructed.  p is where to append to it,
     initially &ret then SCM_CDRLOC of the last pair.  lst progresses as
     elements are considered.

     Elements to be retained are not immediately copied, instead keeplst is
     the last pair in lst which is to be retained but not yet copied, count
     is how many from there are wanted.  When there's no more deletions, *p
     can be set to keeplst to share the remainder of the original lst.  (The
     entire original lst if there's no deletions at all.)  */

  keeplst = lst;
  count = 0;
  p = &ret;

  for ( ; scm_is_pair (lst); lst = SCM_CDR (lst))
    {
      if (scm_is_true (scm_call_2 (pred, x, SCM_CAR (lst))))
        {
          /* delete this element, so copy those at keeplst */
          p = list_copy_part (keeplst, count, p);
          keeplst = SCM_CDR (lst);
          count = 0;
        }
      else
        {
          /* keep this element */
          count++;
        }
    }

  /* final retained elements */
  *p = keeplst;

  /* demand that lst was a proper list */
  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (lst), lst, SCM_ARG2, FUNC_NAME, "list");

  return ret;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_delete_x, "delete!", 2, 1, 0,
            (SCM x, SCM lst, SCM pred),
	    "Return a list containing the elements of @var{lst} but with\n"
	    "those equal to @var{x} deleted.  The returned elements will be\n"
	    "in the same order as they were in @var{lst}.\n"
	    "\n"
	    "Equality is determined by @var{pred}, or @code{equal?} if not\n"
	    "given.  An equality call is made just once for each element,\n"
	    "but the order in which the calls are made on the elements is\n"
	    "unspecified.\n"
	    "\n"
	    "The equality calls are always @code{(pred x elem)}, ie.@: the\n"
	    "given @var{x} is first.  This means for instance elements\n"
	    "greater than 5 can be deleted with @code{(delete 5 lst <)}.\n"
	    "\n"
	    "@var{lst} may be modified to construct the returned list.")
#define FUNC_NAME s_scm_srfi1_delete_x
{
  SCM walk;
  SCM *prev;

  if (SCM_UNBNDP (pred))
    return scm_delete_x (x, lst);

  SCM_ASSERT (scm_is_true (scm_procedure_p (pred)), pred, SCM_ARG3, FUNC_NAME);

  for (prev = &lst, walk = lst;
       scm_is_pair (walk);
       walk = SCM_CDR (walk))
    {
      if (scm_is_true (scm_call_2 (pred, x, SCM_CAR (walk))))
	*prev = SCM_CDR (walk);
      else
	prev = SCM_CDRLOC (walk);
    }

  /* demand the input was a proper list */
  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (walk), walk, SCM_ARG2, FUNC_NAME,"list");
  return lst;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_delete_duplicates, "delete-duplicates", 1, 1, 0,
	    (SCM lst, SCM pred),
	    "Return a list containing the elements of @var{lst} but without\n"
	    "duplicates.\n"
	    "\n"
	    "When elements are equal, only the first in @var{lst} is\n"
	    "retained.  Equal elements can be anywhere in @var{lst}, they\n"
	    "don't have to be adjacent.  The returned list will have the\n"
	    "retained elements in the same order as they were in @var{lst}.\n"
	    "\n"
	    "Equality is determined by @var{pred}, or @code{equal?} if not\n"
	    "given.  Calls @code{(pred x y)} are made with element @var{x}\n"
	    "being before @var{y} in @var{lst}.  A call is made at most once\n"
	    "for each combination, but the sequence of the calls across the\n"
	    "elements is unspecified.\n"
	    "\n"
	    "@var{lst} is not modified, but the return might share a common\n"
	    "tail with @var{lst}.\n"
	    "\n"
	    "In the worst case, this is an @math{O(N^2)} algorithm because\n"
	    "it must check each element against all those preceding it.  For\n"
	    "long lists it is more efficient to sort and then compare only\n"
	    "adjacent elements.")
#define FUNC_NAME s_scm_srfi1_delete_duplicates
{
  scm_t_trampoline_2 equal_p;
  SCM  ret, *p, keeplst, item, l;
  int  count, i;

  /* ret is the new list constructed.  p is where to append, initially &ret
     then SCM_CDRLOC of the last pair.  lst is advanced as each element is
     considered.

     Elements retained are not immediately appended to ret, instead keeplst
     is the last pair in lst which is to be kept but is not yet copied.
     Initially this is the first pair of lst, since the first element is
     always retained.

     *p is kept set to keeplst, so ret (inclusive) to lst (exclusive) is all
     the elements retained, making the equality search loop easy.

     If an item must be deleted, elements from keeplst (inclusive) to lst
     (exclusive) must be copied and appended to ret.  When there's no more
     deletions, *p is left set to keeplst, so ret shares structure with the
     original lst.  (ret will be the entire original lst if there are no
     deletions.)  */

  /* skip to end if an empty list (or something invalid) */
  ret = SCM_EOL;

  if (SCM_UNBNDP (pred))
    equal_p = equal_trampoline;
  else
    {
      SCM_VALIDATE_PROC (SCM_ARG2, pred);
      equal_p = scm_call_2;
    }

  keeplst = lst;
  count = 0;
  p = &ret;

  for ( ; scm_is_pair (lst); lst = SCM_CDR (lst))
    {
      item = SCM_CAR (lst);

      /* look for item in "ret" list */
      for (l = ret; scm_is_pair (l); l = SCM_CDR (l))
        {
          if (scm_is_true (equal_p (pred, SCM_CAR (l), item)))
            {
              /* "item" is a duplicate, so copy keeplst onto ret */
            duplicate:
              p = list_copy_part (keeplst, count, p);

              keeplst = SCM_CDR (lst);  /* elem after the one deleted */
              count = 0;
              goto next_elem;
            }
        }

      /* look for item in "keeplst" list
         be careful traversing, in case nasty code changed the cdrs */
      for (i = 0,       l = keeplst;
           i < count && scm_is_pair (l);
           i++,         l = SCM_CDR (l))
        if (scm_is_true (equal_p (pred, SCM_CAR (l), item)))
          goto duplicate;

      /* keep this element */
      count++;

    next_elem:
      ;
    }
  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (lst), lst, SCM_ARG1, FUNC_NAME, "list");

  /* share tail of keeplst items */
  *p = keeplst;

  return ret;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_delete_duplicates_x, "delete-duplicates!", 1, 1, 0,
	    (SCM lst, SCM pred),
	    "Return a list containing the elements of @var{lst} but without\n"
	    "duplicates.\n"
	    "\n"
	    "When elements are equal, only the first in @var{lst} is\n"
	    "retained.  Equal elements can be anywhere in @var{lst}, they\n"
	    "don't have to be adjacent.  The returned list will have the\n"
	    "retained elements in the same order as they were in @var{lst}.\n"
	    "\n"
	    "Equality is determined by @var{pred}, or @code{equal?} if not\n"
	    "given.  Calls @code{(pred x y)} are made with element @var{x}\n"
	    "being before @var{y} in @var{lst}.  A call is made at most once\n"
	    "for each combination, but the sequence of the calls across the\n"
	    "elements is unspecified.\n"
	    "\n"
	    "@var{lst} may be modified to construct the returned list.\n"
	    "\n"
	    "In the worst case, this is an @math{O(N^2)} algorithm because\n"
	    "it must check each element against all those preceding it.  For\n"
	    "long lists it is more efficient to sort and then compare only\n"
	    "adjacent elements.")
#define FUNC_NAME s_scm_srfi1_delete_duplicates_x
{
  scm_t_trampoline_2 equal_p;
  SCM  ret, endret, item, l;

  /* ret is the return list, constructed from the pairs in lst.  endret is
     the last pair of ret, initially the first pair.  lst is advanced as
     elements are considered.  */

  /* skip to end if an empty list (or something invalid) */
  ret = lst;
  if (scm_is_pair (lst))
    {
      if (SCM_UNBNDP (pred))
        equal_p = equal_trampoline;
      else
        {
          SCM_VALIDATE_PROC (SCM_ARG2, pred);
          equal_p = scm_call_2;
        }

      endret = ret;

      /* loop over lst elements starting from second */
      for (;;)
        {
          lst = SCM_CDR (lst);
          if (! scm_is_pair (lst))
            break;
          item = SCM_CAR (lst);

          /* is item equal to any element from ret to endret (inclusive)? */
          l = ret;
          for (;;)
            {
              if (scm_is_true (equal_p (pred, SCM_CAR (l), item)))
                break;  /* equal, forget this element */

              if (scm_is_eq (l, endret))
                {
                  /* not equal to any, so append this pair */
                  SCM_SETCDR (endret, lst);
                  endret = lst;
                  break;
                }
              l = SCM_CDR (l);
            }
        }

      /* terminate, in case last element was deleted */
      SCM_SETCDR (endret, SCM_EOL);
    }

  /* demand that lst was a proper list */
  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (lst), lst, SCM_ARG1, FUNC_NAME, "list");

  return ret;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_drop_right, "drop-right", 2, 0, 0,
            (SCM lst, SCM n),
	    "Return a new list containing all except the last @var{n}\n"
	    "elements of @var{lst}.")
#define FUNC_NAME s_scm_srfi1_drop_right
{
  SCM tail = scm_list_tail (lst, n);
  SCM ret = SCM_EOL;
  SCM *rend = &ret;
  while (scm_is_pair (tail))
    {
      *rend = scm_cons (SCM_CAR (lst), SCM_EOL);
      rend = SCM_CDRLOC (*rend);
      
      lst = SCM_CDR (lst);
      tail = SCM_CDR (tail);
    }
  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P(tail), tail, SCM_ARG1, FUNC_NAME, "list");
  return ret;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_drop_right_x, "drop-right!", 2, 0, 0,
            (SCM lst, SCM n),
	    "Return the a list containing the @var{n} last elements of\n"
	    "@var{lst}.  @var{lst} may be modified to build the return.")
#define FUNC_NAME s_scm_srfi1_drop_right_x
{
  SCM tail, *p;

  if (scm_is_eq (n, SCM_INUM0))
    return lst;

  tail = scm_list_tail (lst, n);
  p = &lst;

  /* p and tail work along the list, p being the cdrloc of the cell n steps
     behind tail */
  for ( ; scm_is_pair (tail); tail = SCM_CDR (tail))
    p = SCM_CDRLOC (*p);

  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P(tail), tail, SCM_ARG1, FUNC_NAME, "list");

  *p = SCM_EOL;
  return lst;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_drop_while, "drop-while", 2, 0, 0,
            (SCM pred, SCM lst),
	    "Drop the longest initial prefix of @var{lst} whose elements all\n"
	    "satisfy the predicate @var{pred}.")
#define FUNC_NAME s_scm_srfi1_drop_while
{
  SCM_VALIDATE_PROC (SCM_ARG1, pred);

  for ( ; scm_is_pair (lst); lst = SCM_CDR (lst))
    if (scm_is_false (scm_call_1 (pred, SCM_CAR (lst))))
      goto done;

  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (lst), lst, SCM_ARG2, FUNC_NAME, "list");
 done:
  return lst;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_eighth, "eighth", 1, 0, 0,
            (SCM lst),
	    "Return the eighth element of @var{lst}.")
#define FUNC_NAME s_scm_srfi1_eighth
{
  return scm_list_ref (lst, SCM_I_MAKINUM (7));
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_fifth, "fifth", 1, 0, 0,
            (SCM lst),
	    "Return the fifth element of @var{lst}.")
#define FUNC_NAME s_scm_srfi1_fifth
{
  return scm_list_ref (lst, SCM_I_MAKINUM (4));
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_filter_map, "filter-map", 2, 0, 1,
            (SCM proc, SCM list1, SCM rest),
	    "Apply @var{proc} to to the elements of @var{list1} @dots{} and\n"
	    "return a list of the results as per SRFI-1 @code{map}, except\n"
	    "that any @code{#f} results are omitted from the list returned.")
#define FUNC_NAME s_scm_srfi1_filter_map
{
  SCM  ret, *loc, elem, newcell, lst;
  int  argnum;

  SCM_VALIDATE_REST_ARGUMENT (rest);

  ret = SCM_EOL;
  loc = &ret;

  if (scm_is_null (rest))
    {
      /* one list */
      SCM_VALIDATE_PROC (SCM_ARG1, proc);

      for ( ; scm_is_pair (list1); list1 = SCM_CDR (list1))
        {
          elem = scm_call_1 (proc, SCM_CAR (list1));
          if (scm_is_true (elem))
            {
              newcell = scm_cons (elem, SCM_EOL);
              *loc = newcell;
              loc = SCM_CDRLOC (newcell);
            }
        }

      /* check below that list1 is a proper list, and done */
    end_list1:
      lst = list1;
      argnum = 2;
    }
  else if (scm_is_null (SCM_CDR (rest)))
    {
      /* two lists */
      SCM list2 = SCM_CAR (rest);
      SCM_VALIDATE_PROC (SCM_ARG1, proc);

      for (;;)
        {
          if (! scm_is_pair (list1))
            goto end_list1;
          if (! scm_is_pair (list2))
            {
              lst = list2;
              argnum = 3;
              goto check_lst_and_done;
            }
          elem = scm_call_2 (proc, SCM_CAR (list1), SCM_CAR (list2));
          if (scm_is_true (elem))
            {
              newcell = scm_cons (elem, SCM_EOL);
              *loc = newcell;
              loc = SCM_CDRLOC (newcell);
            }
          list1 = SCM_CDR (list1);
          list2 = SCM_CDR (list2);
        }
    }
  else
    {
      /* three or more lists */
      SCM  vec, args, a;
      size_t len, i;

      /* vec is the list arguments */
      vec = scm_vector (scm_cons (list1, rest));
      len = SCM_SIMPLE_VECTOR_LENGTH (vec);

      /* args is the argument list to pass to proc, same length as vec,
         re-used for each call */
      args = scm_make_list (SCM_I_MAKINUM (len), SCM_UNDEFINED);

      for (;;)
        {
          /* first elem of each list in vec into args, and step those
             vec entries onto their next element */
          for (i = 0, a = args, argnum = 2;
               i < len;
               i++, a = SCM_CDR (a), argnum++)
            {
              lst = SCM_SIMPLE_VECTOR_REF (vec, i);  /* list argument */
              if (! scm_is_pair (lst))
                goto check_lst_and_done;
              SCM_SETCAR (a, SCM_CAR (lst));  /* arg for proc */
              SCM_SIMPLE_VECTOR_SET (vec, i, SCM_CDR (lst));  /* rest of lst */
            }

          elem = scm_apply (proc, args, SCM_EOL);
          if (scm_is_true (elem))
            {
              newcell = scm_cons (elem, SCM_EOL);
              *loc = newcell;
              loc = SCM_CDRLOC (newcell);
            }
        }
    }

 check_lst_and_done:
  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (lst), lst, argnum, FUNC_NAME, "list");
  return ret;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_find, "find", 2, 0, 0,
            (SCM pred, SCM lst),
	    "Return the first element of @var{lst} which satisfies the\n"
	    "predicate @var{pred}, or return @code{#f} if no such element is\n"
	    "found.")
#define FUNC_NAME s_scm_srfi1_find
{
  SCM_VALIDATE_PROC (SCM_ARG1, pred);

  for ( ; scm_is_pair (lst); lst = SCM_CDR (lst))
    {
      SCM elem = SCM_CAR (lst);
      if (scm_is_true (scm_call_1 (pred, elem)))
        return elem;
    }
  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (lst), lst, SCM_ARG2, FUNC_NAME, "list");

  return SCM_BOOL_F;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_find_tail, "find-tail", 2, 0, 0,
            (SCM pred, SCM lst),
	    "Return the first pair of @var{lst} whose @sc{car} satisfies the\n"
	    "predicate @var{pred}, or return @code{#f} if no such element is\n"
	    "found.")
#define FUNC_NAME s_scm_srfi1_find_tail
{
  SCM_VALIDATE_PROC (SCM_ARG1, pred);

  for ( ; scm_is_pair (lst); lst = SCM_CDR (lst))
    if (scm_is_true (scm_call_1 (pred, SCM_CAR (lst))))
      return lst;
  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (lst), lst, SCM_ARG2, FUNC_NAME, "list");

  return SCM_BOOL_F;
}
#undef FUNC_NAME

SCM
scm_srfi1_fold (SCM proc, SCM init, SCM list1, SCM rest)
{
  CACHE_VAR (fold, "fold");
  return scm_apply_3 (fold, proc, init, list1, rest);
}

SCM
scm_srfi1_last (SCM lst)
{
  CACHE_VAR (last, "last");
  return scm_call_1 (last, lst);
}

SCM_DEFINE (scm_srfi1_length_plus, "length+", 1, 0, 0,
            (SCM lst),
	    "Return the length of @var{lst}, or @code{#f} if @var{lst} is\n"
	    "circular.")
#define FUNC_NAME s_scm_srfi1_length_plus
{
  long len = scm_ilength (lst);
  return (len >= 0 ? SCM_I_MAKINUM (len) : SCM_BOOL_F);
}
#undef FUNC_NAME


SCM
scm_srfi1_list_index (SCM pred, SCM list1, SCM rest)
{
  CACHE_VAR (list_index, "list-index");
  return scm_apply_2 (list_index, pred, list1, rest);
}

/* This routine differs from the core list-copy in allowing improper lists.
   Maybe the core could allow them similarly.  */

SCM_DEFINE (scm_srfi1_list_copy, "list-copy", 1, 0, 0, 
            (SCM lst),
	    "Return a copy of the given list @var{lst}.\n"
	    "\n"
	    "@var{lst} can be a proper or improper list.  And if @var{lst}\n"
	    "is not a pair then it's treated as the final tail of an\n"
	    "improper list and simply returned.")
#define FUNC_NAME s_scm_srfi1_list_copy
{
  SCM newlst;
  SCM * fill_here;
  SCM from_here;

  newlst = lst;
  fill_here = &newlst;
  from_here = lst;

  while (scm_is_pair (from_here))
    {
      SCM c;
      c = scm_cons (SCM_CAR (from_here), SCM_CDR (from_here));
      *fill_here = c;
      fill_here = SCM_CDRLOC (c);
      from_here = SCM_CDR (from_here);
    }
  return newlst;
}
#undef FUNC_NAME

SCM
scm_srfi1_list_tabulate (SCM n, SCM proc)
{
  CACHE_VAR (list_tabulate, "list-tabulate");
  return scm_call_2 (list_tabulate, n, proc);
}

SCM_DEFINE (scm_srfi1_lset_adjoin, "lset-adjoin", 2, 0, 1,
            (SCM equal, SCM lst, SCM rest),
	    "Add to @var{list} any of the given @var{elem}s not already in\n"
	    "the list.  @var{elem}s are @code{cons}ed onto the start of\n"
	    "@var{list} (so the return shares a common tail with\n"
	    "@var{list}), but the order they're added is unspecified.\n"
	    "\n"
	    "The given @var{=} procedure is used for comparing elements,\n"
	    "called as @code{(@var{=} listelem elem)}, ie.@: the second\n"
	    "argument is one of the given @var{elem} parameters.\n"
	    "\n"
	    "@example\n"
	    "(lset-adjoin eqv? '(1 2 3) 4 1 5) @result{} (5 4 1 2 3)\n"
	    "@end example")
#define FUNC_NAME s_scm_srfi1_lset_adjoin
{
  SCM l, elem;

  SCM_VALIDATE_PROC (SCM_ARG1, equal);
  SCM_VALIDATE_REST_ARGUMENT (rest);

  /* It's not clear if duplicates among the `rest' elements are meant to be
     cast out.  The spec says `=' is called as (= list-elem rest-elem),
     suggesting perhaps not, but the reference implementation shows the
     "list" at each stage as including those "rest" elements already added.
     The latter corresponds to what's described for lset-union, so that's
     what's done here.  */

  for ( ; scm_is_pair (rest); rest = SCM_CDR (rest))
    {
      elem = SCM_CAR (rest);

      for (l = lst; scm_is_pair (l); l = SCM_CDR (l))
        if (scm_is_true (scm_call_2 (equal, SCM_CAR (l), elem)))
          goto next_elem; /* elem already in lst, don't add */

      SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P(l), lst, SCM_ARG2, FUNC_NAME, "list");

      /* elem is not equal to anything already in lst, add it */
      lst = scm_cons (elem, lst);

    next_elem:
      ;
    }

  return lst;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_lset_difference_x, "lset-difference!", 2, 0, 1,
            (SCM equal, SCM lst, SCM rest),
	    "Return @var{lst} with any elements in the lists in @var{rest}\n"
	    "removed (ie.@: subtracted).  For only one @var{lst} argument,\n"
	    "just that list is returned.\n"
	    "\n"
	    "The given @var{equal} procedure is used for comparing elements,\n"
	    "called as @code{(@var{equal} elem1 elemN)}.  The first argument\n"
	    "is from @var{lst} and the second from one of the subsequent\n"
	    "lists.  But exactly which calls are made and in what order is\n"
	    "unspecified.\n"
	    "\n"
	    "@example\n"
	    "(lset-difference! eqv? (list 'x 'y))           @result{} (x y)\n"
	    "(lset-difference! eqv? (list 1 2 3) '(3 1))    @result{} (2)\n"
	    "(lset-difference! eqv? (list 1 2 3) '(3) '(2)) @result{} (1)\n"
	    "@end example\n"
	    "\n"
	    "@code{lset-difference!} may modify @var{lst} to form its\n"
	    "result.")
#define FUNC_NAME s_scm_srfi1_lset_difference_x
{
  SCM ret, *pos, elem, r, b;
  int argnum;

  SCM_VALIDATE_PROC (SCM_ARG1, equal);
  SCM_VALIDATE_REST_ARGUMENT (rest);

  ret = SCM_EOL;
  pos = &ret;
  for ( ; scm_is_pair (lst); lst = SCM_CDR (lst))
    {
      elem = SCM_CAR (lst);

      for (r = rest, argnum = SCM_ARG3;
           scm_is_pair (r);
           r = SCM_CDR (r), argnum++)
        {
          for (b = SCM_CAR (r); scm_is_pair (b); b = SCM_CDR (b))
            if (scm_is_true (scm_call_2 (equal, elem, SCM_CAR (b))))
              goto next_elem; /* equal to elem, so drop that elem */

          SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (b), b, argnum, FUNC_NAME,"list");
        }

      /* elem not equal to anything in later lists, so keep it */
      *pos = lst;
      pos = SCM_CDRLOC (lst);

    next_elem:
      ;
    }
  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (lst), lst, SCM_ARG2, FUNC_NAME, "list");

  *pos = SCM_EOL;
  return ret;
}
#undef FUNC_NAME


/* Typechecking for multi-argument MAP and FOR-EACH.

   Verify that each element of the vector ARGV, except for the first,
   is a list and return minimum length.  Attribute errors to WHO,
   and claim that the i'th element of ARGV is WHO's i+2'th argument.  */
static inline int
check_map_args (SCM argv,
		long len,
		SCM gf,
		SCM proc,
		SCM args,
		const char *who)
{
  long i;
  SCM elt;

  for (i = SCM_SIMPLE_VECTOR_LENGTH (argv) - 1; i >= 1; i--)
    {
      long elt_len;
      elt = SCM_SIMPLE_VECTOR_REF (argv, i);

      if (!(scm_is_null (elt) || scm_is_pair (elt)))
	goto check_map_error;
	
      elt_len = srfi1_ilength (elt);
      if (elt_len < -1)
	goto check_map_error;

      if (len < 0 || (elt_len >= 0 && elt_len < len))
	len = elt_len;
    }

  if (len < 0)
    {
      /* i == 0 */
      elt = SCM_EOL;
    check_map_error:
      if (gf)
	scm_apply_generic (gf, scm_cons (proc, args));
      else
	scm_wrong_type_arg (who, i + 2, elt);
    }

  scm_remember_upto_here_1 (argv);
  return len;
}


SCM_GPROC (s_srfi1_map, "map", 2, 0, 1, scm_srfi1_map, g_srfi1_map);

/* Note: Currently, scm_srfi1_map applies PROC to the argument list(s)
   sequentially, starting with the first element(s).  This is used in
   the Scheme procedure `map-in-order', which guarantees sequential
   behaviour, is implemented using scm_map.  If the behaviour changes,
   we need to update `map-in-order'.
*/

SCM 
scm_srfi1_map (SCM proc, SCM arg1, SCM args)
#define FUNC_NAME s_srfi1_map
{
  long i, len;
  SCM res = SCM_EOL;
  SCM *pres = &res;

  len = srfi1_ilength (arg1);
  SCM_GASSERTn ((scm_is_null (arg1) || scm_is_pair (arg1)) && len >= -1,
		g_srfi1_map,
		scm_cons2 (proc, arg1, args), SCM_ARG2, s_srfi1_map);
  SCM_VALIDATE_REST_ARGUMENT (args);
  if (scm_is_null (args))
    {
      SCM_GASSERT2 (scm_is_true (scm_procedure_p (proc)), g_srfi1_map,
                    proc, arg1, SCM_ARG1, s_srfi1_map);
      SCM_GASSERT2 (len >= 0, g_srfi1_map, proc, arg1, SCM_ARG2, s_srfi1_map);
      while (SCM_NIMP (arg1))
	{
	  *pres = scm_list_1 (scm_call_1 (proc, SCM_CAR (arg1)));
	  pres = SCM_CDRLOC (*pres);
	  arg1 = SCM_CDR (arg1);
	}
      return res;
    }
  if (scm_is_null (SCM_CDR (args)))
    {
      SCM arg2 = SCM_CAR (args);
      int len2 = srfi1_ilength (arg2);
      SCM_GASSERTn (scm_is_true (scm_procedure_p (proc)), g_srfi1_map,
		    scm_cons2 (proc, arg1, args), SCM_ARG1, s_srfi1_map);
      if (len < 0 || (len2 >= 0 && len2 < len))
	len = len2;
      SCM_GASSERTn ((scm_is_null (arg2) || scm_is_pair (arg2))
		    && len >= 0 && len2 >= -1,
		    g_srfi1_map,
		    scm_cons2 (proc, arg1, args),
		    len2 >= 0 ? SCM_ARG2 : SCM_ARG3,
		    s_srfi1_map);
      while (len > 0)
	{
	  *pres = scm_list_1 (scm_call_2 (proc, SCM_CAR (arg1), SCM_CAR (arg2)));
	  pres = SCM_CDRLOC (*pres);
	  arg1 = SCM_CDR (arg1);
	  arg2 = SCM_CDR (arg2);
	  --len;
	}
      return res;
    }
  args = scm_vector (arg1 = scm_cons (arg1, args));
  len = check_map_args (args, len, g_srfi1_map, proc, arg1, s_srfi1_map);
  while (len > 0)
    {
      arg1 = SCM_EOL;
      for (i = SCM_SIMPLE_VECTOR_LENGTH (args) - 1; i >= 0; i--)
	{
	  SCM elt = SCM_SIMPLE_VECTOR_REF (args, i);
	  arg1 = scm_cons (SCM_CAR (elt), arg1);
	  SCM_SIMPLE_VECTOR_SET (args, i, SCM_CDR (elt));
	}
      *pres = scm_list_1 (scm_apply (proc, arg1, SCM_EOL));
      pres = SCM_CDRLOC (*pres);
      --len;
    }
  return res;
}
#undef FUNC_NAME

SCM_REGISTER_PROC (s_srfi1_map_in_order, "map-in-order", 2, 0, 1, scm_srfi1_map);

SCM_GPROC (s_srfi1_for_each, "for-each", 2, 0, 1, scm_srfi1_for_each, g_srfi1_for_each);

SCM 
scm_srfi1_for_each (SCM proc, SCM arg1, SCM args)
#define FUNC_NAME s_srfi1_for_each
{
  long i, len;
  len = srfi1_ilength (arg1);
  SCM_GASSERTn ((scm_is_null (arg1) || scm_is_pair (arg1)) && len >= -1,
		g_srfi1_for_each, scm_cons2 (proc, arg1, args),
		SCM_ARG2, s_srfi1_for_each);
  SCM_VALIDATE_REST_ARGUMENT (args);
  if (scm_is_null (args))
    {
      SCM_GASSERT2 (scm_is_true (scm_procedure_p (proc)), g_srfi1_for_each,
                    proc, arg1, SCM_ARG1, s_srfi1_for_each);
      SCM_GASSERT2 (len >= 0, g_srfi1_for_each, proc, arg1,
		    SCM_ARG2, s_srfi1_map);
      while (SCM_NIMP (arg1))
	{
	  scm_call_1 (proc, SCM_CAR (arg1));
	  arg1 = SCM_CDR (arg1);
	}
      return SCM_UNSPECIFIED;
    }
  if (scm_is_null (SCM_CDR (args)))
    {
      SCM arg2 = SCM_CAR (args);
      int len2 = srfi1_ilength (arg2);
      SCM_GASSERTn (scm_is_true (scm_procedure_p (proc)), g_srfi1_for_each,
		    scm_cons2 (proc, arg1, args), SCM_ARG1, s_srfi1_for_each);
      if (len < 0 || (len2 >= 0 && len2 < len))
	len = len2;
      SCM_GASSERTn ((scm_is_null (arg2) || scm_is_pair (arg2))
		    && len >= 0 && len2 >= -1,
		    g_srfi1_for_each,
		    scm_cons2 (proc, arg1, args),
		    len2 >= 0 ? SCM_ARG2 : SCM_ARG3,
		    s_srfi1_for_each);
      while (len > 0)
	{
	  scm_call_2 (proc, SCM_CAR (arg1), SCM_CAR (arg2));
	  arg1 = SCM_CDR (arg1);
	  arg2 = SCM_CDR (arg2);
	  --len;
	}
      return SCM_UNSPECIFIED;
    }
  args = scm_vector (arg1 = scm_cons (arg1, args));
  len = check_map_args (args, len, g_srfi1_for_each, proc, arg1,
			s_srfi1_for_each);
  while (len > 0)
    {
      arg1 = SCM_EOL;
      for (i = SCM_SIMPLE_VECTOR_LENGTH (args) - 1; i >= 0; i--)
	{
	  SCM elt = SCM_SIMPLE_VECTOR_REF (args, i);
	  arg1 = scm_cons (SCM_CAR (elt), arg1);
	  SCM_SIMPLE_VECTOR_SET (args, i, SCM_CDR (elt));
	}
      scm_apply (proc, arg1, SCM_EOL);
      --len;
    }
  return SCM_UNSPECIFIED;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_member, "member", 2, 1, 0,
           (SCM x, SCM lst, SCM pred),
	    "Return the first sublist of @var{lst} whose @sc{car} is equal\n"
	    "to @var{x}.  If @var{x} does not appear in @var{lst}, return\n"
	    "@code{#f}.\n"
	    "\n"
	    "Equality is determined by @code{equal?}, or by the equality\n"
	    "predicate @var{=} if given.  @var{=} is called @code{(= @var{x}\n"
	    "elem)}, ie.@: with the given @var{x} first, so for example to\n"
	    "find the first element greater than 5,\n"
	    "\n"
	    "@example\n"
	    "(member 5 '(3 5 1 7 2 9) <) @result{} (7 2 9)\n"
	    "@end example\n"
	    "\n"
	    "This version of @code{member} extends the core @code{member} by\n"
	    "accepting an equality predicate.")
#define FUNC_NAME s_scm_srfi1_member
{
  scm_t_trampoline_2 equal_p;
  SCM_VALIDATE_LIST (2, lst);
  if (SCM_UNBNDP (pred))
    equal_p = equal_trampoline;
  else
    {
      SCM_VALIDATE_PROC (SCM_ARG3, pred);
      equal_p = scm_call_2;
    }
  for (; !SCM_NULL_OR_NIL_P (lst); lst = SCM_CDR (lst))
    {
      if (scm_is_true (equal_p (pred, x, SCM_CAR (lst))))
	return lst;
    }
  return SCM_BOOL_F;
}
#undef FUNC_NAME

SCM_DEFINE (scm_srfi1_assoc, "assoc", 2, 1, 0,
	    (SCM key, SCM alist, SCM pred),
	    "Behaves like @code{assq} but uses third argument @var{pred?}\n"
	    "for key comparison.  If @var{pred?} is not supplied,\n"
	    "@code{equal?} is used.  (Extended from R5RS.)\n")
#define FUNC_NAME s_scm_srfi1_assoc
{
  SCM ls = alist;
  scm_t_trampoline_2 equal_p;
  if (SCM_UNBNDP (pred))
    equal_p = equal_trampoline;
  else
    {
      SCM_VALIDATE_PROC (SCM_ARG3, pred);
      equal_p = scm_call_2;
    }
  for(; scm_is_pair (ls); ls = SCM_CDR (ls)) 
    {
      SCM tmp = SCM_CAR (ls);
      SCM_ASSERT_TYPE (scm_is_pair (tmp), alist, SCM_ARG2, FUNC_NAME,
		       "association list");
      if (scm_is_true (equal_p (pred, key, SCM_CAR (tmp))))
	return tmp;
    }
  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (ls), alist, SCM_ARG2, FUNC_NAME,
		   "association list");
  return SCM_BOOL_F;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_ninth, "ninth", 1, 0, 0,
            (SCM lst),
	    "Return the ninth element of @var{lst}.")
#define FUNC_NAME s_scm_srfi1_ninth
{
  return scm_list_ref (lst, scm_from_int (8));
}
#undef FUNC_NAME

SCM
scm_srfi1_not_pair_p (SCM obj)
{
  CACHE_VAR (not_pair_p, "not-pair?");
  return scm_call_1 (not_pair_p, obj);
}

SCM_DEFINE (scm_srfi1_partition, "partition", 2, 0, 0,
	    (SCM pred, SCM list),
	    "Partition the elements of @var{list} with predicate @var{pred}.\n"
	    "Return two values: the list of elements satifying @var{pred} and\n"
	    "the list of elements @emph{not} satisfying @var{pred}.  The order\n"
	    "of the output lists follows the order of @var{list}.  @var{list}\n"
	    "is not mutated.  One of the output lists may share memory with @var{list}.\n")
#define FUNC_NAME s_scm_srfi1_partition
{
  /* In this implementation, the output lists don't share memory with
     list, because it's probably not worth the effort. */
  SCM orig_list = list;
  SCM kept = scm_cons(SCM_EOL, SCM_EOL);
  SCM kept_tail = kept;
  SCM dropped = scm_cons(SCM_EOL, SCM_EOL);
  SCM dropped_tail = dropped;
  
  SCM_VALIDATE_PROC (SCM_ARG1, pred);
  
  for (; !SCM_NULL_OR_NIL_P (list); list = SCM_CDR(list)) {
    SCM elt, new_tail;

    /* Make sure LIST is not a dotted list.  */
    SCM_ASSERT (scm_is_pair (list), orig_list, SCM_ARG2, FUNC_NAME);

    elt = SCM_CAR (list);
    new_tail = scm_cons (SCM_CAR (list), SCM_EOL);

    if (scm_is_true (scm_call_1 (pred, elt))) {
      SCM_SETCDR(kept_tail, new_tail);
      kept_tail = new_tail;
    }
    else {
      SCM_SETCDR(dropped_tail, new_tail);
      dropped_tail = new_tail;
    }
  }
  /* re-use the initial conses for the values list */
  SCM_SETCAR(kept, SCM_CDR(kept));
  SCM_SETCDR(kept, dropped);
  SCM_SETCAR(dropped, SCM_CDR(dropped));
  SCM_SETCDR(dropped, SCM_EOL);
  return scm_values(kept);
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_partition_x, "partition!", 2, 0, 0,
            (SCM pred, SCM lst),
	    "Split @var{lst} into those elements which do and don't satisfy\n"
	    "the predicate @var{pred}.\n"
	    "\n"
	    "The return is two values (@pxref{Multiple Values}), the first\n"
	    "being a list of all elements from @var{lst} which satisfy\n"
	    "@var{pred}, the second a list of those which do not.\n"
	    "\n"
	    "The elements in the result lists are in the same order as in\n"
	    "@var{lst} but the order in which the calls @code{(@var{pred}\n"
	    "elem)} are made on the list elements is unspecified.\n"
	    "\n"
	    "@var{lst} may be modified to construct the return lists.")
#define FUNC_NAME s_scm_srfi1_partition_x
{
  SCM  tlst, flst, *tp, *fp;

  SCM_ASSERT (scm_is_true (scm_procedure_p (pred)), pred, SCM_ARG1, FUNC_NAME);

  /* tlst and flst are the lists of true and false elements.  tp and fp are
     where to store to append to them, initially &tlst and &flst, then
     SCM_CDRLOC of the last pair in the respective lists.  */

  tlst = SCM_EOL;
  flst = SCM_EOL;
  tp = &tlst;
  fp = &flst;

  for ( ; scm_is_pair (lst); lst = SCM_CDR (lst))
    {
      if (scm_is_true (scm_call_1 (pred, SCM_CAR (lst))))
        {
          *tp = lst;
          tp = SCM_CDRLOC (lst);
        }
      else
        {
          *fp = lst;
          fp = SCM_CDRLOC (lst);
        }
    }

  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (lst), lst, SCM_ARG2, FUNC_NAME, "list");

  /* terminate whichever didn't get the last element(s) */
  *tp = SCM_EOL;
  *fp = SCM_EOL;

  return scm_values (scm_list_2 (tlst, flst));
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_reduce, "reduce", 3, 0, 0,
            (SCM proc, SCM def, SCM lst),
	    "@code{reduce} is a variant of @code{fold}, where the first call\n"
	    "to @var{proc} is on two elements from @var{lst}, rather than\n"
	    "one element and a given initial value.\n"
	    "\n"
	    "If @var{lst} is empty, @code{reduce} returns @var{def} (this is\n"
	    "the only use for @var{def}).  If @var{lst} has just one element\n"
	    "then that's the return value.  Otherwise @var{proc} is called\n"
	    "on the elements of @var{lst}.\n"
	    "\n"
	    "Each @var{proc} call is @code{(@var{proc} @var{elem}\n"
	    "@var{previous})}, where @var{elem} is from @var{lst} (the\n"
	    "second and subsequent elements of @var{lst}), and\n"
	    "@var{previous} is the return from the previous call to\n"
	    "@var{proc}.  The first element of @var{lst} is the\n"
	    "@var{previous} for the first call to @var{proc}.\n"
	    "\n"
	    "For example, the following adds a list of numbers, the calls\n"
	    "made to @code{+} are shown.  (Of course @code{+} accepts\n"
	    "multiple arguments and can add a list directly, with\n"
	    "@code{apply}.)\n"
	    "\n"
	    "@example\n"
	    "(reduce + 0 '(5 6 7)) @result{} 18\n"
	    "\n"
	    "(+ 6 5)  @result{} 11\n"
	    "(+ 7 11) @result{} 18\n"
	    "@end example\n"
	    "\n"
	    "@code{reduce} can be used instead of @code{fold} where the\n"
	    "@var{init} value is an ``identity'', meaning a value which\n"
	    "under @var{proc} doesn't change the result, in this case 0 is\n"
	    "an identity since @code{(+ 5 0)} is just 5.  @code{reduce}\n"
	    "avoids that unnecessary call.")
#define FUNC_NAME s_scm_srfi1_reduce
{
  SCM ret;
  SCM_VALIDATE_PROC (SCM_ARG1, proc);
  ret = def;  /* if lst is empty */
  if (scm_is_pair (lst))
    {
      ret = SCM_CAR (lst);  /* if lst has one element */

      for (lst = SCM_CDR (lst); scm_is_pair (lst); lst = SCM_CDR (lst))
        ret = scm_call_2 (proc, SCM_CAR (lst), ret);
    }

  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (lst), lst, SCM_ARG3, FUNC_NAME, "list");
  return ret;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_reduce_right, "reduce-right", 3, 0, 0,
            (SCM proc, SCM def, SCM lst),
	    "@code{reduce-right} is a variant of @code{fold-right}, where\n"
	    "the first call to @var{proc} is on two elements from @var{lst},\n"
	    "rather than one element and a given initial value.\n"
	    "\n"
	    "If @var{lst} is empty, @code{reduce-right} returns @var{def}\n"
	    "(this is the only use for @var{def}).  If @var{lst} has just\n"
	    "one element then that's the return value.  Otherwise @var{proc}\n"
	    "is called on the elements of @var{lst}.\n"
	    "\n"
	    "Each @var{proc} call is @code{(@var{proc} @var{elem}\n"
	    "@var{previous})}, where @var{elem} is from @var{lst} (the\n"
	    "second last and then working back to the first element of\n"
	    "@var{lst}), and @var{previous} is the return from the previous\n"
	    "call to @var{proc}.  The last element of @var{lst} is the\n"
	    "@var{previous} for the first call to @var{proc}.\n"
	    "\n"
	    "For example, the following adds a list of numbers, the calls\n"
	    "made to @code{+} are shown.  (Of course @code{+} accepts\n"
	    "multiple arguments and can add a list directly, with\n"
	    "@code{apply}.)\n"
	    "\n"
	    "@example\n"
	    "(reduce-right + 0 '(5 6 7)) @result{} 18\n"
	    "\n"
	    "(+ 6 7)  @result{} 13\n"
	    "(+ 5 13) @result{} 18\n"
	    "@end example\n"
	    "\n"
	    "@code{reduce-right} can be used instead of @code{fold-right}\n"
	    "where the @var{init} value is an ``identity'', meaning a value\n"
	    "which under @var{proc} doesn't change the result, in this case\n"
	    "0 is an identity since @code{(+ 7 0)} is just 5.\n"
	    "@code{reduce-right} avoids that unnecessary call.\n"
	    "\n"
	    "@code{reduce} should be preferred over @code{reduce-right} if\n"
	    "the order of processing doesn't matter, or can be arranged\n"
	    "either way, since @code{reduce} is a little more efficient.")
#define FUNC_NAME s_scm_srfi1_reduce_right
{
  /* To work backwards across a list requires either repeatedly traversing
     to get each previous element, or using some memory for a reversed or
     random-access form.  Repeated traversal might not be too terrible, but
     is of course quadratic complexity and hence to be avoided in case LST
     is long.  A vector is preferred over a reversed list since it's more
     compact and is less work for the gc to collect.  */

  SCM vec, ret;
  ssize_t len, i;
  SCM_VALIDATE_PROC (SCM_ARG1, proc);
  if (SCM_NULL_OR_NIL_P (lst))
    return def;

  vec = scm_vector (lst);
  len = SCM_SIMPLE_VECTOR_LENGTH (vec);

  ret = SCM_SIMPLE_VECTOR_REF (vec, len-1);
  for (i = len-2; i >= 0; i--)
    ret = scm_call_2 (proc, SCM_SIMPLE_VECTOR_REF (vec, i), ret);

  return ret;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_remove, "remove", 2, 0, 0,
	    (SCM pred, SCM list),
	    "Return a list containing all elements from @var{lst} which do\n"
	    "not satisfy the predicate @var{pred}.  The elements in the\n"
	    "result list have the same order as in @var{lst}.  The order in\n"
	    "which @var{pred} is applied to the list elements is not\n"
	    "specified.")
#define FUNC_NAME s_scm_srfi1_remove
{
  SCM walk;
  SCM *prev;
  SCM res = SCM_EOL;
  SCM_VALIDATE_PROC (SCM_ARG1, pred);
  SCM_VALIDATE_LIST (2, list);
  
  for (prev = &res, walk = list;
       scm_is_pair (walk);
       walk = SCM_CDR (walk))
    {
      if (scm_is_false (scm_call_1 (pred, SCM_CAR (walk))))
	{
	  *prev = scm_cons (SCM_CAR (walk), SCM_EOL);
	  prev = SCM_CDRLOC (*prev);
	}
    }

  return res;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_remove_x, "remove!", 2, 0, 0,
	    (SCM pred, SCM list),
	    "Return a list containing all elements from @var{list} which do\n"
	    "not satisfy the predicate @var{pred}.  The elements in the\n"
	    "result list have the same order as in @var{list}.  The order in\n"
	    "which @var{pred} is applied to the list elements is not\n"
	    "specified.  @var{list} may be modified to build the return\n"
	    "list.")
#define FUNC_NAME s_scm_srfi1_remove_x
{
  SCM walk;
  SCM *prev;
  SCM_VALIDATE_PROC (SCM_ARG1, pred);
  SCM_VALIDATE_LIST (2, list);
  
  for (prev = &list, walk = list;
       scm_is_pair (walk);
       walk = SCM_CDR (walk))
    {
      if (scm_is_false (scm_call_1 (pred, SCM_CAR (walk))))
	prev = SCM_CDRLOC (walk);
      else
	*prev = SCM_CDR (walk);
    }

  return list;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_seventh, "seventh", 1, 0, 0,
            (SCM lst),
	    "Return the seventh element of @var{lst}.")
#define FUNC_NAME s_scm_srfi1_seventh
{
  return scm_list_ref (lst, scm_from_int (6));
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_sixth, "sixth", 1, 0, 0,
            (SCM lst),
	    "Return the sixth element of @var{lst}.")
#define FUNC_NAME s_scm_srfi1_sixth
{
  return scm_list_ref (lst, scm_from_int (5));
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_span, "span", 2, 0, 0,
            (SCM pred, SCM lst),
	    "Return two values, the longest initial prefix of @var{lst}\n"
	    "whose elements all satisfy the predicate @var{pred}, and the\n"
	    "remainder of @var{lst}.")
#define FUNC_NAME s_scm_srfi1_span
{
  SCM ret, *p;

  SCM_ASSERT (scm_is_true (scm_procedure_p (pred)), pred, SCM_ARG1, FUNC_NAME);

  ret = SCM_EOL;
  p = &ret;
  for ( ; scm_is_pair (lst); lst = SCM_CDR (lst))
    {
      SCM elem = SCM_CAR (lst);
      if (scm_is_false (scm_call_1 (pred, elem)))
        goto done;

      /* want this elem, tack it onto the end of ret */
      *p = scm_cons (elem, SCM_EOL);
      p = SCM_CDRLOC (*p);
    }
  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (lst), lst, SCM_ARG2, FUNC_NAME, "list");

 done:
  return scm_values (scm_list_2 (ret, lst));
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_span_x, "span!", 2, 0, 0,
            (SCM pred, SCM lst),
	    "Return two values, the longest initial prefix of @var{lst}\n"
	    "whose elements all satisfy the predicate @var{pred}, and the\n"
	    "remainder of @var{lst}.  @var{lst} may be modified to form the\n"
	    "return.")
#define FUNC_NAME s_scm_srfi1_span_x
{
  SCM upto, *p;

  SCM_ASSERT (scm_is_true (scm_procedure_p (pred)), pred, SCM_ARG1, FUNC_NAME);

  p = &lst;
  for (upto = lst; scm_is_pair (upto); upto = SCM_CDR (upto))
    {
      if (scm_is_false (scm_call_1 (pred, SCM_CAR (upto))))
        goto done;

      /* want this element */
      p = SCM_CDRLOC (upto);
    }
  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (upto), lst, SCM_ARG2, FUNC_NAME, "list");

 done:
  *p = SCM_EOL;
  return scm_values (scm_list_2 (lst, upto));
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_split_at, "split-at", 2, 0, 0,
            (SCM lst, SCM n),
	    "Return two values (multiple values), being a list of the\n"
	    "elements before index @var{n} in @var{lst}, and a list of those\n"
	    "after.")
#define FUNC_NAME s_scm_srfi1_split_at
{
  size_t nn;
  /* pre is a list of elements before the i split point, loc is the CDRLOC
     of the last cell, ie. where to store to append to it */
  SCM pre = SCM_EOL;
  SCM *loc = &pre;

  for (nn = scm_to_size_t (n); nn != 0; nn--)
    {
      SCM_VALIDATE_CONS (SCM_ARG1, lst);

      *loc = scm_cons (SCM_CAR (lst), SCM_EOL);
      loc = SCM_CDRLOC (*loc);
      lst = SCM_CDR(lst);
    }
  return scm_values (scm_list_2 (pre, lst));
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_split_at_x, "split-at!", 2, 0, 0,
            (SCM lst, SCM n),
	    "Return two values (multiple values), being a list of the\n"
	    "elements before index @var{n} in @var{lst}, and a list of those\n"
	    "after.  @var{lst} is modified to form those values.")
#define FUNC_NAME s_scm_srfi1_split_at
{
  size_t nn;
  SCM upto = lst;
  SCM *loc = &lst;

  for (nn = scm_to_size_t (n); nn != 0; nn--)
    {
      SCM_VALIDATE_CONS (SCM_ARG1, upto);

      loc = SCM_CDRLOC (upto);
      upto = SCM_CDR (upto);
    }

  *loc = SCM_EOL;
  return scm_values (scm_list_2 (lst, upto));
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_take_x, "take!", 2, 0, 0,
            (SCM lst, SCM n),
	    "Return a list containing the first @var{n} elements of\n"
	    "@var{lst}.")
#define FUNC_NAME s_scm_srfi1_take_x
{
  long nn;
  SCM pos;

  nn = scm_to_signed_integer (n, 0, LONG_MAX);
  if (nn == 0)
    return SCM_EOL;

  pos = scm_list_tail (lst, scm_from_long (nn - 1));

  /* Must have at least one cell left, mustn't have reached the end of an
     n-1 element list.  SCM_VALIDATE_CONS here gives the same error as
     scm_list_tail does on say an n-2 element list, though perhaps a range
     error would make more sense (for both).  */
  SCM_VALIDATE_CONS (SCM_ARG1, pos);

  SCM_SETCDR (pos, SCM_EOL);
  return lst;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_take_right, "take-right", 2, 0, 0,
            (SCM lst, SCM n),
	    "Return the a list containing the @var{n} last elements of\n"
	    "@var{lst}.")
#define FUNC_NAME s_scm_srfi1_take_right
{
  SCM tail = scm_list_tail (lst, n);
  while (scm_is_pair (tail))
    {
      lst = SCM_CDR (lst);
      tail = SCM_CDR (tail);
    }
  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P(tail), tail, SCM_ARG1, FUNC_NAME, "list");
  return lst;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_take_while, "take-while", 2, 0, 0,
            (SCM pred, SCM lst),
	    "Return a new list which is the longest initial prefix of\n"
	    "@var{lst} whose elements all satisfy the predicate @var{pred}.")
#define FUNC_NAME s_scm_srfi1_take_while
{
  SCM ret, *p;

  SCM_ASSERT (scm_is_true (scm_procedure_p (pred)), pred, SCM_ARG1, FUNC_NAME);

  ret = SCM_EOL;
  p = &ret;
  for ( ; scm_is_pair (lst); lst = SCM_CDR (lst))
    {
      SCM elem = SCM_CAR (lst);
      if (scm_is_false (scm_call_1 (pred, elem)))
        goto done;

      /* want this elem, tack it onto the end of ret */
      *p = scm_cons (elem, SCM_EOL);
      p = SCM_CDRLOC (*p);
    }
  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (lst), lst, SCM_ARG2, FUNC_NAME, "list");

 done:
  return ret;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_take_while_x, "take-while!", 2, 0, 0,
            (SCM pred, SCM lst),
	    "Return the longest initial prefix of @var{lst} whose elements\n"
	    "all satisfy the predicate @var{pred}.  @var{lst} may be\n"
	    "modified to form the return.")
#define FUNC_NAME s_scm_srfi1_take_while_x
{
  SCM upto, *p;

  SCM_ASSERT (scm_is_true (scm_procedure_p (pred)), pred, SCM_ARG1, FUNC_NAME);

  p = &lst;
  for (upto = lst; scm_is_pair (upto); upto = SCM_CDR (upto))
    {
      if (scm_is_false (scm_call_1 (pred, SCM_CAR (upto))))
        goto done;

      /* want this element */
      p = SCM_CDRLOC (upto);
    }
  SCM_ASSERT_TYPE (SCM_NULL_OR_NIL_P (upto), lst, SCM_ARG2, FUNC_NAME, "list");

 done:
  *p = SCM_EOL;
  return lst;
}
#undef FUNC_NAME


SCM_DEFINE (scm_srfi1_tenth, "tenth", 1, 0, 0,
            (SCM lst),
	    "Return the tenth element of @var{lst}.")
#define FUNC_NAME s_scm_srfi1_tenth
{
  return scm_list_ref (lst, scm_from_int (9));
}
#undef FUNC_NAME


SCM
scm_srfi1_xcons (SCM d, SCM a)
{
  CACHE_VAR (xcons, "xcons");
  return scm_call_2 (xcons, d, a);
}


void
scm_init_srfi_1 (void)
{
  SCM the_root_module = scm_lookup_closure_module (SCM_BOOL_F);
#ifndef SCM_MAGIC_SNARFER
#include "srfi/srfi-1.x"
#endif
  scm_c_extend_primitive_generic
    (SCM_VARIABLE_REF (scm_c_module_lookup (the_root_module, "map")),
     SCM_VARIABLE_REF (scm_c_lookup ("map")));
  scm_c_extend_primitive_generic
    (SCM_VARIABLE_REF (scm_c_module_lookup (the_root_module, "for-each")),
     SCM_VARIABLE_REF (scm_c_lookup ("for-each")));
}

/* End of srfi-1.c.  */