14 Sep
2006
14 Sep
'06
12:02 p.m.
Hello Brian, Thursday, September 14, 2006, 7:43:55 PM, you wrote:
Even if the compiler did know, by some other means, that a Node had been wrapped, Haskell doesn't support true existentials
whereas you'd really need an existential:
getCommon :: (forall gc. Node gc) -> Common
they are supported in ghc 6.6 with name of "impredicative polymorphism", section 7.4.9 or 7.4.10 of new user manual -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com