Re: Liberalising IncoherentInstances

29 Jul 2013

      ...
AntC  writes:
Uh-oh, quoted the wrong example. I mean:

Starting with:

    class C a b | a -> b where foo :: a -> b
    instance C [a] [a] where foo = id

    t11 = \x -> foo [x]     -- t11 :: t -> [t]

I then added:

    instance C [Char] [Char] where foo = id
                     -- more specific!
    t12 = \x -> [x]  -- t12 :: C [t] [t] => t -> [t]
                     -- more polymorphic!