[m-rev.] array.m changes to increase completeness guarantees

[Peter Moulder]

Estimated hours taken: 0.5

library/array.m:
	Improve completeness guarantees by using if-then-else's to ensure that
	operations that can throw an exception are really conditional on bounds
	checks.
	This also allows us to call the `unsafe' (unchecked) versions directly.


Index: array.m
===================================================================
RCS file: /home/mercury1/repository/mercury/library/array.m,v
retrieving revision 1.123
diff -d -u -r1.123 library/array.m
--- library/array.m	11 Jun 2003 12:55:49 -0000	1.123
+++ library/array.m	8 Aug 2003 05:58:39 -0000
@@ -382,9 +382,14 @@
 :- pragma export(array_equal(in, in), "ML_array_equal").
 
 array_equal(Array1, Array2) :-
-	array__size(Array1, Size),
-	array__size(Array2, Size),
-	array__equal_elements(0, Size, Array1, Array2).
+	( if
+		array__size(Array1, Size),
+		array__size(Array2, Size)
+	then
+		array__equal_elements(0, Size, Array1, Array2)
+	else
+		fail
+	).
 
 :- pred array__equal_elements(int, int, array(T), array(T)).
 :- mode array__equal_elements(in, in, in, in) is semidet.
@@ -656,16 +661,25 @@
 	Min =< Index, Index =< Max.
 
 array__semidet_lookup(Array, Index, Item) :-
-	array__in_bounds(Array, Index),
-	array__lookup(Array, Index, Item).
+	( if array__in_bounds(Array, Index) then
+		array__unsafe_lookup(Array, Index, Item)
+	else
+		fail
+	).
 
 array__semidet_set(Array0, Index, Item, Array) :-
-	array__in_bounds(Array0, Index),
-	array__set(Array0, Index, Item, Array).
+	( if array__in_bounds(Array0, Index) then
+		array__unsafe_set(Array0, Index, Item, Array)
+	else
+		fail
+	).
 
 array__semidet_slow_set(Array0, Index, Item, Array) :-
-	array__in_bounds(Array0, Index),
-	array__slow_set(Array0, Index, Item, Array).
+	( if array__in_bounds(Array0, Index) then
+		array__slow_set(Array0, Index, Item, Array)
+	else
+		fail
+	).
 
 array__slow_set(Array0, Index, Item, Array) :-
 	array__copy(Array0, Array1),
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