[Haskell-cafe] Strange error with type classes + associated types

[Brent Yorgey]

On Thu, Apr 15, 2010 at 12:48:20AM +1000, Roman Leshchinskiy wrote:
> 
> > 
> > Right, this seems weird to me.  Why is there still a 'u' mentioned in
> > the constraints?  Actually, I don't even see why there ought to be
> > both v and v1.  The type of (*.*) mentions three type variables, u, v, and w:
> > 
> > (*.*)  :: (HasBasis  u, HasTrie  (Basis  u), 
> >           HasBasis  v, HasTrie  (Basis  v), 
> >           VectorSpace  w, 
> >           Scalar  v ~ Scalar  w) 
> >       => (v :-*  w) -> (u :-*  v) -> u :-*  w
> 
> Note that (:-*) is a type synonym:
> 
> type :-* u v = MSum (Basis u :->: v)

Aha!  That's what I was missing.  Thanks for the insight, Roman.  I
guess it's time to go bug Conal... =)

-Brent