Oh, that is my fault - I was sure that I specified the extension and it didn't help. It really works with Overlapping&Undecidable. Thank you! On Wed, Feb 27, 2013 at 10:36 PM, Aleksey Khudyakov < alexey.skladnoy@gmail.com> wrote:
On 27.02.2013 17:35, Dmitry Kulagin wrote:
Hi Aleksey,
Unfortunately, your solution does not work for me (ghc 7.6.2). I reduced the problem to:
-- | Type class for type equality. class TypeEq (a :: α) (b :: α) (eq :: Bool) | a b -> eq instance TypeEq a a True -- instance TypeEq a b False instance eq ~ False => TypeEq a b eq
You need to add pragma {-# LANGUAGE OverlappingInstances #-} to the file where instances defined. Without it GHC will complain about overlap and unlike other extensions won't recommend pragma