[m-rev.] for review: improve check for invalid invalid declarations

[Mark Brown]

On 28-Sep-2007, Peter Ross <pro at missioncriticalit.com> wrote:
> 
> For juliensf or pwa to review.
> 
> ===================================================================
> 
> 
> Estimated hours taken: 4
> Branches: main
> 
> Improve check for invalid instance declarations.
> 
> compiler/check_typeclass.m:
> 	Check that each type in the instance declaration is a type with
> 	no arguments of a polymorphic type whose arguments are all distinct
> 	type variables.

Hmm, there is already code to check this in parse_underived_instance_2
in prog_io_typeclass.m.  I'm a bit puzzled why it apparently isn't working.
Any clue?

In any case, putting the check in the front end pass is a good idea, and
is better than checking during parsing, IMHO.

Cheers,
Mark.

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