Re: [Haskell-cafe] Non-atomic "atoms" for type-level programming

29 Apr 2009


      Hi again,

Tillmann Rendel wrote:
...
{-# LANGUAGE TypeFamilies #-}
  module D (ok) where
    import A
    import B
data D client = D client
type family Label client
    type instance A.Label (D client) = D.Label client
    type instance B.Label (D client) = D.Label client
ok :: client -> [D.Label client]
    ok client = [ A.z (D client), B.z (D client)]
Oh, and note that I do not need UndecidableInstances here, because I 
match against the explicit module identity D.

   Tillmann