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

[Bulat Ziganshin]

Hello haskell-cafe,

now i'm reading Haskell' proposals and found that these two things
considered as different:

http://hackage.haskell.org/trac/haskell-prime/wiki/ExistentialQuantification
http://hackage.haskell.org/trac/haskell-prime/wiki/PolymorphicComponents

can you please explain me what is the difference between

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

and

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

?

-- 
Best regards,
 Bulat                          mailto:Bulat.Ziganshin at gmail.com