[m-rev.] For review: Introduce stack.mamber/2 to standard library.

[Paul Bone]

For review by anyone.

Estimated Hours taken: 0.2
Branches: main

Introduce stack.member(Elem, Stack), which is true of Elem is somewhere
within the stack Stack.

library/stack.m:
	As above'

NEWS:
	Announce the change.

Index: NEWS
===================================================================
RCS file: /home/mercury1/repository/mercury/NEWS,v
retrieving revision 1.497
diff -u -p -b -r1.497 NEWS
--- NEWS	23 Sep 2008 06:42:24 -0000	1.497
+++ NEWS	11 Oct 2008 07:02:09 -0000
@@ -122,6 +122,9 @@ Changes to the Mercury standard library:
 * We have changed the interface of the ops module to make lookups of operators
   more efficient.
 
+* The following predicates have been added to the stack module:
+    stack.member/2
+
 * We have added io.update_globals/3 which allows for atomic updates to
   the globals field in the I/O state in the presence of multiple threads.
 
Index: library/stack.m
===================================================================
RCS file: /home/mercury1/repository/mercury/library/stack.m,v
retrieving revision 1.26
diff -u -p -b -r1.26 stack.m
--- library/stack.m	2 Jun 2008 04:55:00 -0000	1.26
+++ library/stack.m	11 Oct 2008 06:58:21 -0000
@@ -82,6 +82,10 @@
 :- pred stack.depth(stack(T)::in, int::out) is det.
 :- func stack.depth(stack(T)) = int.
 
+    % 'stack.member(Elem, Stack)' is true iff 'Elem' is contained in the stack.
+    %
+:- pred stack.member(T::in, stack(T)::in) is semidet.
+
 %--------------------------------------------------------------------------%
 %--------------------------------------------------------------------------%
 
@@ -135,6 +139,9 @@ stack.det_pop(Stack0, Elem, Stack) :-
 stack.depth(stack(Elems), Depth) :-
 	list.length(Elems, Depth).
 
+stack.member(Elem, stack(List)) :-
+    list.member(Elem, List).
+
 %--------------------------------------------------------------------------%
 %--------------------------------------------------------------------------%
 % Ralph Becket <rwab1 at cl.cam.ac.uk> 29/04/99
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