Add `vhash-fold-right'.

* module/ice-9/vlist.scm (vhash-fold-right): New procedure.

* test-suite/tests/vlist.test ("vhash")["vhash-fold-right"]: New test.

* doc/ref/api-compound.texi (VHashes): Document `vhash-fold-right'.

doc/ref/api-compound.texi

@@ -1,7 +1,7 @@
 @c -*-texinfo-*-
 @c This is part of the GNU Guile Reference Manual.
-@c Copyright (C)  1996, 1997, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2009, 2010
-@c   Free Software Foundation, Inc.
+@c Copyright (C)  1996, 1997, 2000, 2001, 2002, 2003, 2004, 2005, 2006,
+@c   2007, 2009, 2010, 2011  Free Software Foundation, Inc.
 @c See the file guile.texi for copying conditions.
 
 @node Compound Data Types
@@ -3294,8 +3294,9 @@ Again the choice of @var{hash-proc} must be consistent with previous calls to
 @end deffn
 
 @deffn {Scheme Procedure} vhash-fold proc vhash
-Fold over the key/pair elements of @var{vhash}.  For each pair call @var{proc}
-as @code{(@var{proc} key value result)}.
+@deffnx {Scheme Procedure} vhash-fold-right proc vhash
+Fold over the key/value elements of @var{vhash} in the given direction.
+For each pair call @var{proc} as @code{(@var{proc} key value result)}.
 @end deffn
 
 @deffn {Scheme Procedure} vhash-fold* proc init key vhash [equal? [hash]]

module/ice-9/vlist.scm

@@ -33,7 +33,7 @@
             vhash? vhash-cons vhash-consq vhash-consv
             vhash-assoc vhash-assq vhash-assv
             vhash-delete vhash-delq vhash-delv
-            vhash-fold
+            vhash-fold vhash-fold-right
             vhash-fold* vhash-foldq* vhash-foldv*
             alist->vhash))
 
@@ -560,6 +560,16 @@ with @var{equal?}."
               seed
               vhash))
 
+(define (vhash-fold-right proc seed vhash)
+  "Fold over the key/pair elements of @var{vhash}, starting from the 0th
+element.  For each pair call @var{proc} as @code{(@var{proc} key value
+result)}."
+  (vlist-fold-right (lambda (key+value result)
+                      (proc (car key+value) (cdr key+value)
+                            result))
+                    seed
+                    vhash))
+
 (define* (alist->vhash alist #:optional (hash hash))
   "Return the vhash corresponding to @var{alist}, an association list."
   (fold-right (lambda (pair result)

test-suite/tests/vlist.test

@@ -301,6 +301,13 @@
            (alist  (fold alist-cons '() keys values)))
       (equal? alist (reverse (vhash-fold alist-cons '() vh)))))
 
+  (pass-if "vhash-fold-right"
+    (let* ((keys   '(a b c d e f g d h i))
+           (values '(1 2 3 4 5 6 7 0 8 9))
+           (vh     (fold vhash-cons vlist-null keys values))
+           (alist  (fold alist-cons '() keys values)))
+      (equal? alist (vhash-fold-right alist-cons '() vh))))
+
   (pass-if "alist->vhash"
     (let* ((keys   '(a b c d e f g d h i))
            (values '(1 2 3 4 5 6 7 0 8 9))