[m-dev.] trivial diff: use implication in typecheck

[David Glen JEFFERY]

Estimated hours taken: 0.1

compiler/typecheck.m:
	Change some code to use universal quantification and implication
	rather than a less inteligible series of negations and
	implicit existential quantifications. (This code was previously
	commented out because SICStus wouldn't accept it).

Index: compiler/typecheck.m
===================================================================
RCS file: /home/staff/zs/imp/mercury/compiler/typecheck.m,v
retrieving revision 1.279
diff -u -t -r1.279 typecheck.m
--- compiler/typecheck.m	2000/09/16 00:08:04	1.279
+++ compiler/typecheck.m	2000/08/23 07:48:22
@@ -445,7 +445,7 @@
                         PredInfo4),
 
                 %
-                % Split the inferred type class constraints into those that
+                % Split the inferred type class constraints into those 
                 % that apply only to the head variables, and those that
                 % apply to type variables which occur only in the body.
                 %
@@ -4227,19 +4227,10 @@
 :- mode check_satisfiability(in, in) is semidet.
 
 check_satisfiability(Constraints, HeadTypeParams) :-
-        % SICStus doesn't allow the following syntax
-        % all [C] list__member(C, Constraints) => (
-        %       C = constraint(_ClassName, Types),
-        %       term__contains_var_list(Types, TVar),
-        %       not list__member(TVar, HeadTypeParams)
-        % ).
-        \+ (
-                list__member(C, Constraints),
-                \+ (
-                        C = constraint(_ClassName, Types),
-                        term__contains_var_list(Types, TVar),
-                        \+ list__member(TVar, HeadTypeParams)
-                )
+        all [C] list__member(C, Constraints) => (
+                C = constraint(_ClassName, Types),
+                term__contains_var_list(Types, TVar),
+                not list__member(TVar, HeadTypeParams)
         ).
 
 %-----------------------------------------------------------------------------%


dgj
-- 
David Jeffery (dgj at cs.mu.oz.au) | If your thesis is utterly vacuous
PhD student,                    | Use first-order predicate calculus.
Dept. of Comp. Sci. & Soft. Eng.|     With sufficient formality
The University of Melbourne     |     The sheerist banality
Australia                       | Will be hailed by the critics: "Miraculous!"
                                |     -- Anon.
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