[m-rev.] Tiny addition to store.m

[Ralph Becket]

Estimated hours taken: 1
Branches: main

A useful addition to store.m.

library/store.m:
	Added copy_mutvar/4.
	Fixed an over-long line.

Index: library/store.m
===================================================================
RCS file: /home/mercury1/repository/mercury/library/store.m,v
retrieving revision 1.34
diff -u -r1.34 store.m
--- library/store.m	14 Jun 2002 10:18:55 -0000	1.34
+++ library/store.m	29 Jan 2003 01:21:48 -0000
@@ -62,6 +62,14 @@
 :- pred store__new_mutvar(T, generic_mutvar(T, S), S, S) <= store(S).
 :- mode store__new_mutvar(in, out, di, uo) is det.
 
+	% copy_mutvar(OldMutvar, NewMutvar, S0, S)
+	% is equivalent to the sequence
+	% 	get_mutvar(OldMutvar, Value, S0, S1),
+	% 	new_mutvar(NewMutvar, Value, S1, S )
+:- pred store__copy_mutvar(generic_mutvar(T, S), generic_mutvar(T, S), S, S)
+		<= store(S).
+:- mode store__copy_mutvar(in, out, di, uo) is det.
+
 	% lookup the value stored in a given mutable variable
 :- pred store__get_mutvar(generic_mutvar(T, S), T, S, S) <= store(S).
 :- mode store__get_mutvar(in, out, di, uo) is det.
@@ -302,6 +310,10 @@
 	% matching foreign_proc version.
 	{ private_builtin__sorry("store__new_mutvar") }.
 
+copy_mutvar(Mutvar, Copy) -->
+	get_mutvar(Mutvar, Value),
+	new_mutvar(Value, Copy).
+
 get_mutvar(_, _) -->
 	% This version is only used for back-ends for which there is no
 	% matching foreign_proc version.
@@ -316,7 +328,8 @@
 						S, S) <= store(S).
 :- mode store__unsafe_new_uninitialized_mutvar(out, di, uo) is det.
 
-:- pragma foreign_proc("C", unsafe_new_uninitialized_mutvar(Mutvar::out, S0::di, S::uo),
+:- pragma foreign_proc("C",
+		unsafe_new_uninitialized_mutvar(Mutvar::out, S0::di, S::uo),
 		[will_not_call_mercury, promise_pure],
 "
 	MR_incr_hp_msg(Mutvar, 1, MR_PROC_LABEL, ""store:mutvar/2"");
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