[Haskell-cafe] Strange error with type classes + associated types
byorgey at seas.upenn.edu
Mon Apr 19 00:02:12 EDT 2010
Thanks for looking into this! Making (:-*) into a proper type seems
promising. I did try wrapping (:-*) in a newtype but that didn't
help (although I didn't expect it to).
I see you just uploaded a new version of vector-space; what's new in
On Sat, Apr 17, 2010 at 10:28:45AM -0700, Conal Elliott wrote:
> Oh! I'd completely forgotten about this idea. Looking at Data.LinearMap in
> vector-space, I see a comment about exactly this ambiguity, as well as the
> start of a new module that wraps a data type around the linear map
> representation. I don't recall whether I got stuck or just distracted.
> On Sat, Apr 17, 2010 at 3:46 AM, Roman Leshchinskiy <rl at cse.unsw.edu.au>wrote:
> > On 17/04/2010, at 11:00, Conal Elliott wrote:
> > > I'm unsure now, but I think I tried making Basis a data type (not syn)
> > and ran into the problem I mentioned above. The Basis *synonyms* also have
> > HasTrie instances, which is crucially important. If we switch to
> > (injective) data types, then we lose the HasTrie instances. I'd be okay
> > with defining HasTrie instances (preferably via "deriving") for the
> > associated Basis data types, but I couldn't figure out how to. Maybe it's
> > not possible currently, or maybe I just didn't know how.
> > Could you perhaps make (:-*) a proper type rather than a synonym? That
> > would help with the ambiguity.
> > Roman
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