[mercury-users] type class bug?

Nicholas Nethercote njn at csse.unimelb.edu.au
Thu Jun 22 18:44:49 AEST 2006

On Thu, 22 Jun 2006, Mark Brown wrote:

> It's a known limitation in the typeclass system when using equivalence
> types.  Unfortunately, Julien's suggestion won't work because of another
> limitation: the arguments of instances must be of the form foo(A, B, ...).
> Try defining the above types as:
> 	:- type type_expr ---> raw_type_expr - src_locn.
> 	:- type expr ---> raw_expr - src_locn.
> Or something similar using a better constructor than '-'/2.

Hmm, that's frustrating.  I'd rather not have to change my data structures 
to workaround compiler shortcomings.  How fundamental is the shortcoming --
how hard would it be to implement?  I'm just curious.

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