Re: [Haskell-cafe] Solved but strange error in type inference

As I understand it, both ways work.

legSome ((LegGram g)::LegGram nt t s) ntV

If you compile this without ScopedTypeVariables extension, GHC will remind you of it:

Illegal signature in pattern: LegGram nt t s Use -XScopedTypeVariables to permit it

So another solution is to avoid the ugly redundancy is:

legSome :: forall nt t s . LegGram nt t s -> nt -> Either String ([t], s)