28 Feb
2011
28 Feb
'11
6:34 a.m.
On 2/28/11 6:01 AM, Yves Parès wrote:
takeC :: Int -> Compoz a b -> (exists c. Compoz a c) dropC :: Int -> Compoz a b -> (exists c. Compoz c b)
What does 'exists' means? To create a rank-2 type can't you use:
takeC :: Int -> Compoz a b -> (forall c. Compoz a c)
??
For any A and T, foo :: A -> (forall b. T b) is identical to foo :: forall b. (A -> T b) More technically, they're isomorphic--- in System F or any other gritty language that makes you explicitly pass types around. Since Haskell handles type passing implicitly, the isomorphism looks like identity. -- Live well, ~wren