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

Roman Leshchinskiy rl at cse.unsw.edu.au
Sat Apr 17 06:46:47 EDT 2010

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.


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