[Haskell-cafe] Rank-2 types and class constraints

[Stefan Holdermans]

Hi,

Just out of curiosity (I cannot come up with a practical example):  Why 
doesn't the following piece of code type check in GHC (with 
extensions)?

 > foo :: (forall a . (Eq a) => a) -> Integer
 > foo =  undefined

It seems like the type-class constraint is playing a decisive rôle 
here, since the following does check.

 > bar :: (forall a . a) -> Integer
 > bar =  undefined

TIA,

Stefan