17 Dec
2009
17 Dec
'09
2:10 p.m.
{-# LANGUAGE GADTs, TypeFamilies #-} module Assoc where data EqD k where EqD :: Eq k => EqD k class MyClass k where data AssociatedType k :: * evidence :: AssociatedType k -> EqD (AssociatedType k) eq :: MyClass k => AssociatedType k -> AssociatedType k -> Bool -- eq k1 k2 = k1 == k2 -- doesn't work eq k1 k2 = case evidence k1 of EqD -> k1 == k2 -- works fine On 17 Dec 2009, at 16:37, Stephen Lavelle wrote:
class MyClass k where type AssociatedType k :: *