> On Jun 17, 2018, at 10:01 AM, sasa bogicevic <[email protected]> wrote:
>
> So I guess that we need to check if one of the kinds of two types we are
> comparing defaults to * (or Type if you will) and then
> add new warning that will be more descriptive as to why the failure happened.
> Maybe there is a way to check if what we are
> comparing are actually type families so that would make the job easier I
> guess.
I don't think the problem is particular to `Type` or defaulting. Instead, the
problem is when one of the two mismatched types is a type family application
where the type family has equations that pattern-match on an invisible
parameter, and it's that invisible-parameter matching that's gone awry. Now
that I think about it, detecting these particular conditions might be tricky:
you might need to edit code in FamInstEnv that does type family equation lookup
to return diagnostic information if a match fails. (I would look at
reduceTyFamApp_maybe, and perhaps it can return something more interesting than
Nothing in the failure case.)
>
> Richard Eisenberg offered some help on this but I am not sure how to grab
> hold of him so I'd appreciate any help I could get.
>
Just email! :)
Thanks for looking into this!
Richard
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