[m-rev.] for review: fix existential typeclass reordering bug

[Simon Taylor]

On 12-Jun-2002, Fergus Henderson <fjh at cs.mu.OZ.AU> wrote:
> On 12-Jun-2002, Simon Taylor <stayl at cs.mu.OZ.AU> wrote:
> > 
> > +	%
> > +	% For code which requires mode reordering, we may have
> > +	% already seen some of the type-infos produced by this
> > +	% call. The type-info locations for those variables will
> > +	% be a type-info
> > +	%
> > +	list__foldl2(polymorphism__maybe_extract_type_info(OldTypeInfoMap),
> > +		TVars, [], ExtraGoals, PolyInfo2, PolyInfo).
> 
> That comment looks incomplete.

--- polymorphism.m	2002/06/11 16:11:27	1.2
+++ polymorphism.m	2002/06/11 16:22:29
@@ -2624,16 +2624,15 @@
 
 	constraint_list_get_tvars(ExistentialConstraints, TVars0),
 	list__sort_and_remove_dups(TVars0, TVars),
-
-	%
-	% For code which requires mode reordering, we may have
-	% already seen some of the type-infos produced by this
-	% call. The type-info locations for those variables will
-	% be a type-info
-	%
 	list__foldl2(polymorphism__maybe_extract_type_info(OldTypeInfoMap),
 		TVars, [], ExtraGoals, PolyInfo2, PolyInfo).
 
+	% For code which requires mode reordering, we may have already
+	% seen uses of some of the type variables produced by this call.
+	% At the point of the use of a type variable that we haven't seen
+	% before, we assume that it is unconstrained. If it turns out that
+	% the type variable is constrained, and the type_info is contained
+	% in a typeclass_info, we need to generate code to extract it here.
 :- pred polymorphism__maybe_extract_type_info(type_info_varmap,
 		tvar, list(hlds_goal), list(hlds_goal),
 		poly_info, poly_info).
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