Re: [Haskell-cafe] Scope of type variables in associated types

21 May 2007

      Matthew Sackman wrote:
...
...
class G a where
          data E a :: *
          wrap :: a -> E a
          unwrap :: E a -> a
I'm afraid not. I really need wrap to take a 'b' and unwrap to return a 'b'.
Talking on #haskell to sjanssen last night, he came up with:
How does

  class F a where
      data B a :: *
      data E a :: *
      wrap :: B a -> E a
      unwrap :: E a -> B a

sound? 'B a' would represent the 'b' in your previous attempt,

  class F a b | a -> b where
  ...

Bertram

Re: [Haskell-cafe] Scope of type variables in associated types

Bertram Felgenhauer