Implement list folding functions.

* include/mailutils/list.h (mu_list_folder_t): New typedef.
(mu_list_fold, mu_list_rfold): New functions.
* libmailutils/list/fold.c: New file.
* libmailutils/list/rfold.c: New file.
* libmailutils/list/Makefile.am (liblist_la_SOURCES): Add fold.c and
rfold.c
* libmailutils/list/gmap.c (mu_list_gmap): Access list elements directly,
instead of using iterators.
* libmailutils/tests/list.at: Add test cases for list folding.
* libmailutils/tests/listop.c: Add fold and rfold commands.

@@ -238,7 +238,10 @@ typedef int (*mu_list_mapper_t) (void **_itmv, size_t _itmc, void *_call_data);
    and until all elements from the array have been visited.
 
    Mu_list_gmap returns 0 on success and a non-zero error code on failure.
-   If _map returns non-zero, its return value is propagated to the caller. */
+   If _map returns non-zero, its return value is propagated to the caller.
+
+   The _map function is not allowed to alter the _list.
+*/
    
 int mu_list_gmap (mu_list_t _list, mu_list_mapper_t _map, size_t _nelem,
 		  void *_data);
@@ -263,11 +266,56 @@ int mu_list_gmap (mu_list_t _list, mu_list_mapper_t _map, size_t _nelem,
    MU_LIST_MAP_SKIP bit set, the _itmv[0] element is appended to the new
    list.  If it has MU_LIST_MAP_STOP bit set, iteration is stopped
    immediately and any remaining elements in _list are ignored.
+
+   The mapper function (_map) is not allowed to alter the _list.
 */
 
 int mu_list_map (mu_list_t _list, mu_list_mapper_t _map,
 		 void *_data, size_t _nelem,
 		 mu_list_t *_res);
+
+  /* List fold */
+
+typedef int (*mu_list_folder_t) (void *_item, void *_data,
+				 void *_prev, void **_ret);
+
+  /* mu_list_fold iterates over list elements from first to last.
+     For each element it calls _fold with the following arguments:
+
+       _item     -  the current list element,
+       _data     -  call-specific data,
+       _prev     -  on the first call, _init; on subsequent calls,
+                    points to the value returned from the previous call
+		    to _fold in the _ret varialble,
+       _ret      -  memory location where to store the result of this
+                    call.
+
+     When all elements have been visited, mu_list_fold stores the result
+     of the last _fold invocation (as returned in *_ret) in the memory
+     location pointed to by _return_value.
+
+     If _fold returns a non-zero value, mu_list_fold stops iteration and
+     returns this value.  The *_return_value is filled in this case as
+     well.
+
+     Possible return codes:
+
+       0                   - success,
+       EINVAL              - _list or _fold is NULL,
+       MU_ERR_OUT_PTR_NULL - _return_code is NULL
+       other value         - non-zero value returned by _fold.
+
+     The _fold function is not allowed to alter the list it is being applied
+     to.
+       
+     The mu_list_rfold acts similarly, except that it iterates over list
+     elements from last to first.
+  */
+int mu_list_fold (mu_list_t _list, mu_list_folder_t _fold, void *_data,
+		  void *_init, void *_return_value);
+int mu_list_rfold (mu_list_t _list, mu_list_folder_t _fold, void *_data,
+		   void *_init, void *_return_value);
+  
 #ifdef __cplusplus
 }
 #endif

@@ -25,6 +25,7 @@ liblist_la_SOURCES = \
  create.c\
  destroy.c\
  empty.c\
+ fold.c\
  foreach.c\
  get.c\
  getcomp.c\
@@ -39,6 +40,7 @@ liblist_la_SOURCES = \
  prepend.c\
  remove.c\
  replace.c\
+ rfold.c\
  setcomp.c\
  setdestr.c\
  slice.c\

+/* GNU Mailutils -- a suite of utilities for electronic mail
+   Copyright (C) 2011 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, see 
+   <http://www.gnu.org/licenses/>. */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+#include <stdlib.h>
+#include <mailutils/errno.h>
+#include <mailutils/sys/list.h>
+
+int
+mu_list_fold (mu_list_t list, mu_list_folder_t fold, void *data, void *prev,
+	      void *return_value)
+{
+  struct list_data *current;
+  int status = 0;
+  
+  if (list == NULL || fold == NULL)
+    return EINVAL;
+  if (return_value == NULL)
+    return MU_ERR_OUT_PTR_NULL;
+
+  for (current = list->head.next; current != &list->head;
+       current = current->next)
+    {
+      status = fold (current->item, data, prev, &prev);
+      if (status)
+	break;
+    }
+  *(void **) return_value = prev;
+  return status;
+}

@@ -27,28 +27,21 @@ int
 mu_list_gmap (mu_list_t list, mu_list_mapper_t map, size_t nelem, void *data)
 {
   int rc;
-  int status;
-  mu_iterator_t itr;
+  struct list_data *current;
   void **buf;
   size_t i;
   
   if (!list || !map || nelem == 0)
     return EINVAL;
-  rc = mu_list_get_iterator (list, &itr);
-  if (rc)
-    return status;
   buf = calloc (nelem, sizeof (buf[0]));
   if (!buf)
+    return ENOMEM;
+
+  i = 0;
+  for (current = list->head.next; current != &list->head;
+       current = current->next)
     {
-      mu_iterator_destroy (&itr);
-      return ENOMEM;
-    }
-  for (i = 0, mu_iterator_first (itr); !mu_iterator_is_done (itr);
-       mu_iterator_next (itr))
-    {
-      void *item;
-      mu_iterator_current (itr, &item);
-      buf[i++] = item;
+      buf[i++] = current->item;
       if (i == nelem)
 	{
 	  i = 0;
@@ -59,7 +52,6 @@ mu_list_gmap (mu_list_t list, mu_list_mapper_t map, size_t nelem, void *data)
     }
   if (rc == 0 && i > 0 && i < nelem)
     rc = map (buf, i, data);
-  mu_iterator_destroy (&itr);
   free (buf);
   return rc;
 }

+/* GNU Mailutils -- a suite of utilities for electronic mail
+   Copyright (C) 2011 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, see 
+   <http://www.gnu.org/licenses/>. */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+#include <stdlib.h>
+#include <mailutils/errno.h>
+#include <mailutils/sys/list.h>
+
+int
+mu_list_rfold (mu_list_t list, mu_list_folder_t fold, void *data, void *prev,
+	       void *return_value)
+{
+  struct list_data *current;
+  int status = 0;
+  
+  if (list == NULL || fold == NULL)
+    return EINVAL;
+  if (return_value == NULL)
+    return MU_ERR_OUT_PTR_NULL;
+
+  for (current = list->head.prev; current != &list->head;
+       current = current->prev)
+    {
+      status = fold (current->item, data, prev, &prev);
+      if (status)
+	break;
+    }
+  *(void **) return_value = prev;
+  return status;
+}

@@ -388,6 +388,62 @@ ti
 ])
 
 m4_popdef([MU_TEST_KEYWORDS])
+# ------------------------------------------------------------
+# Fold
+# ------------------------------------------------------------
+
+m4_define([MU_TEST_GROUP],[Fold])
+m4_pushdef([MU_TEST_KEYWORDS],MU_TEST_KEYWORDS[ fold])
+
+TESTLIST([empty list],[],
+[fold
+],
+[NULL
+])
+
+TESTLIST([one element],[],
+[add en
+fold
+],
+[en
+])
+
+TESTLIST([many elements],[],
+[add en to tre fire fem
+fold
+],
+[entotrefirefem
+])
+
+m4_popdef([MU_TEST_KEYWORDS])
+# ------------------------------------------------------------
+# Reverse Fold
+# ------------------------------------------------------------
+
+m4_define([MU_TEST_GROUP],[Reverse Fold])
+m4_pushdef([MU_TEST_KEYWORDS],MU_TEST_KEYWORDS[ rfold])
+
+TESTLIST([empty list],[],
+[rfold
+],
+[NULL
+])
+
+TESTLIST([one element],[],
+[add en
+rfold
+],
+[en
+])
+
+TESTLIST([many elements],[],
+[add en to tre fire fem
+rfold
+],
+[femfiretretoen
+])
+
+m4_popdef([MU_TEST_KEYWORDS])
 
 dnl ------------------------------------------------------------
 dnl Cleanup

@@ -720,6 +720,60 @@ tail (size_t argc, mu_list_t list)
     printf ("%s\n", text);
 }
 
+static int
+fold_concat (void *item, void *data, void *prev, void **ret)
+{
+  char *s;
+  size_t len = strlen (item);
+  size_t prevlen = 0;
+  
+  if (prev)
+    prevlen = strlen (prev);
+
+  s = realloc (prev, len + prevlen + 1);
+  if (!s)
+    abort ();
+  strcpy (s + prevlen, item);
+  *ret = s;
+  return 0;
+}
+
+void
+fold (mu_list_t list)
+{
+  char *text = NULL;
+  int rc;
+
+  rc = mu_list_fold (list, fold_concat, NULL, NULL, &text);
+  if (rc)
+    mu_diag_funcall (MU_DIAG_ERROR, "mu_list_fold", NULL, rc);
+  else if (text)
+    {
+      printf ("%s\n", text);
+      free (text);
+    }
+  else
+    printf ("NULL\n");
+}
+
+void
+rfold (mu_list_t list)
+{
+  char *text = NULL;
+  int rc;
+
+  rc = mu_list_rfold (list, fold_concat, NULL, NULL, &text);
+  if (rc)
+    mu_diag_funcall (MU_DIAG_ERROR, "mu_list_fold", NULL, rc);
+  else if (text)
+    {
+      printf ("%s\n", text);
+      free (text);
+    }
+  else
+    printf ("NULL\n");
+}
+  
 void
 help ()
 {
@@ -739,6 +793,8 @@ help ()
   printf ("ictl ins item [item*]\n");
   printf ("ictl dir [backwards|forwards]\n");
   printf ("map [-replace] NAME [ARGS]\n");
+  printf ("fold\n");
+  printf ("rfold\n");
   printf ("print\n");
   printf ("slice [-replace] num [num...]\n");
   printf ("quit\n");
@@ -813,6 +869,10 @@ shell (mu_list_t list)
 	    print (list);
 	  else if (strcmp (ws.ws_wordv[0], "cur") == 0)
 	    cur (num, itr[num]);
+	  else if (strcmp (ws.ws_wordv[0], "fold") == 0)
+	    fold (list);
+	  else if (strcmp (ws.ws_wordv[0], "rfold") == 0)
+	    rfold (list);
 	  else if (strcmp (ws.ws_wordv[0], "map") == 0)
 	    {
 	      int i;