[mercury-users] type class bug?

[Julien Fischer]

On Thu, 22 Jun 2006, Nicholas Nethercote wrote:

> Hi,
>
> I'm trying to use a type class.
>
> I have these declarations:
>
>    :- typeclass pstr(T) where [ func pstr(T) = string ].
>
>    :- instance pstr(raw_item)  where [ func(pstr/1) is pstr_raw_item  ].
>    :- instance pstr(type_expr) where [ func(pstr/1) is pstr_type_expr ].
>    %:- instance pstr(expr)      where [ func(pstr/1) is pstr_expr      ].
>
> This compiles fine.
>
> If I uncomment the last line, I get this error:

...

Does the error go away if you change the instance decls to:

	:- instance pstr(pair(raw_type_expr, src_locn)).
	:- instance pstr(pair(raw_expr, src_locn)).

Julien.
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