Re[2]: [Haskell-cafe] what is a difference between existential quantification and polymorhic field?

Hello Ross, Thursday, September 21, 2006, 12:55:40 PM, you wrote:

...

data Ex = forall a. Num a => Ex a

and

data Po = Po (forall a. Num a => a)

Consider the types of the constructors:

Ex :: forall a. (Num a) => a -> Ex Po :: (forall a. (Num a) => a) -> Po

sorry, Ross, can you give me a more detailed explanation? it seems that Po argument is existential by itself, but i don't understand that all this mean also, ghc66 adds impredicative polymorphism. how it differs from unqualified existentials? -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com