[Haskell-cafe] Sound typeable via type families?

[Wolfgang Jeltsch]

Am Freitag, 28. März 2008 05:21 schrieb Dan Doel:
> […]

> However, obviously, this depends on overlapping instances (if there's some
> other way, I'd be happy to know; if type inequality contexts are available,
> I wasn't able to find them), and I've heard that type families don't play
> well with overlap. Does that not apply to data families? Will this
> construction still work in 6.10 and beyond?
>
> Also, this doesn't seem to be a suitable basis for Dynamic. Trying to
> extend the GADT solution presented resulted in errors unless incoherent
> instances were turned on (clearly not a good sign), and even then, it
> didn't actually work. Is it possible to do better, and come away with
> something that will actually work for Dynamic, and be sound?

I don’t know exactly whether this helps here but with open type families you 
will be able to define a type-level type equality decision.  See the mail at 
<http://www.haskell.org/pipermail/glasgow-haskell-users/2007-October/013271.html>.

> […]

Best wishes,
Wolfgang