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

[Julien Fischer]

On Fri, 28 Sep 2007, Mark Brown wrote:

> 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.

I pretty sure there is already code to check that the type variables
are distinct.

Julien.
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