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

[Simon Taylor]

On 26-Jul-2002, Simon Taylor <stayl at cs.mu.OZ.AU> wrote:
> 
> Estimated hours taken: 5
> Branches: main
> 
> compiler/typecheck.m:
> 	Fix a bug in the handling of superclass constraints where
> 	some of the argument variables of the subclass don't appear
> 	in the superclass constraint, such as in class `bar' below.
> 	:- typeclass foo(T, U) <= bar(T, U).
> 	:- typeclass bar(T, U) <= baz(T).
> 
> 	When calling a method of baz with a universal constraint in
> 	the predicate declaration of foo(A, B), the variable B
> 	was not being substituted correctly in the constraint
> 	proofs, resulting in an abort in polymorphism.

I've committed this (it's needed to compile the analysis framework).

Simon.
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