[m-dev.] instance declarations

[Mark Brown]

On 05-Mar-2006, Ian MacLarty <maclarty at cs.mu.OZ.AU> wrote:
> Do we still need the restriction that types in instance declarations 
> must be functors with distinct variables as arguments, even when some 
> of those arguments are functionally dependent on other ones?

The restriction is there for implementation reasons.  We definitely plan
to relax it, but it is a non-trivial amount of work to do so.

> Surely 
> you just need the arguments in the domain of the functional dependency 
> to be functors?

See Jones' paper for a better description of the restrictions.

Note that Jones' restrictions are tighter than they need to be, and we
may relax them further in future.  But for the moment, we plan to implement
them that way, and then decide afterwards how much further to go.

Cheers,
Mark.

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