02.10.2011 19:55, David Barbour пишет:
Use TypeFamilies.
{-# LANGUAGE TypeFamilies #}
...
type family FType a :: *
type instance FType Char = Float
type instance FType Double = Int
class ExampleClass a where
f :: a -> FType a
Better to include type in class.
class ExampleClass a where
type FType a
f :: a -> FType a
instance ExampleClass Char where
type FType Char = Float
f char = ...
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