Re: [Haskell-cafe] Pattern synonyms and explicit forall.

The end of your error message:

| 63 | pattern Any a <- Some a | ^

Appears to have program text (a mono-directional pattern binding) that doesn't correspond to the program text you quote. Whereas

pattern Any :: forall a. a -> Some

pattern Any a = Some

Is a implicitly bi-directional pattern binding that will never work. (The free var `a` on LHS does not appear in RHS.) I'm suspecting the explicit forall is not much to do with it.