[m-rev.] for review: add list.cons/3 to list.m

[Julien Fischer]

Add a predicate list.cons/3 to list.m.  This is sometimes
useful with higher-order code and it can make code that
uses state variables more concise.


NEWS:
	Mention these changes.

library/list.m:
	Add the predicate list.cons/3 and export the function
	version that was already there.
library/std_util:
	Remove the cons predicate needed by builtin_solutions/2
	and use the one added above.

Julien.

Index: NEWS
===================================================================
RCS file: /home/mercury1/repository/mercury/NEWS,v
retrieving revision 1.328
diff -u -r1.328 NEWS
--- NEWS	20 Feb 2004 08:00:08 -0000	1.328
+++ NEWS	18 Mar 2004 04:33:21 -0000
@@ -160,6 +160,10 @@
 * We've added some new predicates, list__map2_foldl, list__map_foldl3,
   and list__foldl4 to list.m.

+* We've added a predicate, list__cons/3 to list.m.  This is sometimes
+  useful with higher-order code.  It can also be useful with state
+  variables.  We've also added a function version.
+
 * We've added some new predicates, map__common_subset and map__foldl3,
   to map.m.

Index: library/list.m
===================================================================
RCS file: /home/mercury1/repository/mercury/library/list.m,v
retrieving revision 1.117
diff -u -r1.117 list.m
--- library/list.m	15 Mar 2004 23:49:32 -0000	1.117
+++ library/list.m	18 Mar 2004 04:08:32 -0000
@@ -60,6 +60,12 @@

 :- pred list__is_not_empty(list(T)::in) is semidet.

+	% list__cons(X, Y, Z) <=> Z = [X | Y].
+	%
+:- pred list__cons(T, list(T), list(T)).
+:- mode list__cons(in, in, out) is det.
+:- func list__cons(T, list(T)) = list(T).
+
 	% Standard append predicate:
 	% list__append(Start, End, List) is true iff
 	% `List' is the result of concatenating `Start' and `End'.
@@ -746,6 +752,10 @@

 list__is_not_empty([_ | _]).

+list__cons(H, T, [H | T]).
+
+list__cons(H, T) = [H | T].
+
 list__append([], Ys, Ys).
 list__append([X | Xs], Ys, [X | Zs]) :-
 	list__append(Xs, Ys, Zs).
@@ -1486,10 +1496,7 @@

 empty_list = [].

-:- func cons(T, list(T)) = list(T).
-:- pragma export((cons(in, in) = (out)), "ML_cons").
-
-cons(H, T) = [H | T].
+:- pragma export((list__cons(in, in) = (out)), "ML_cons").

 %-----------------------------------------------------------------------------%
 %-----------------------------------------------------------------------------%
Index: library/std_util.m
===================================================================
RCS file: /home/mercury1/repository/mercury/library/std_util.m,v
retrieving revision 1.292
diff -u -r1.292 std_util.m
--- library/std_util.m	15 Mar 2004 06:50:16 -0000	1.292
+++ library/std_util.m	18 Mar 2004 04:08:19 -0000
@@ -1467,11 +1467,7 @@
 	is det. /* really cc_multi */

 builtin_solutions(Generator, UnsortedList) :-
-	builtin_aggregate(Generator, cons, [], UnsortedList).
-
-:- pred cons(T::in, list(T)::in, list(T)::out) is det.
-
-cons(H, T, [H | T]).
+	builtin_aggregate(Generator, list__cons, [], UnsortedList).

 %-----------------------------------------------------------------------------%


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