I would expect this to work, maybe with some additional notation (a la
ScopedTypeVariables)
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE MultiParamTypeClasses #-}
class Foo a b | a -> b
class Foo a b => Bar a where
foo :: a -> b -> c
The type family equivalent works as expected:
{-# LANGUAGE TypeFamilies #-}
class Foo a where
type T a :: *
class Bar a where
foo :: a -> T a -> c
I can't use type families because the `Foo' I'm using is in an external library.
Is there any way to achieve what I want without adding `b' to `Bar'?
--
Francesco * Often in error, never in doubt
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