Re: [Haskell-cafe] A curios monad

On Thu, Dec 11, 2008 at 1:48 PM, Andrew Coppin <andrewcoppin@btinternet.com> wrote:

BTW, does anybody know how rank-N types are different from existential types?

You mean the Haskell extensions? ExistentialQuantification lets you define types such as, data SomeNum = forall a. Num a => SomeNum a RankNTypes lets you nest foralls arbitrarily deep in type signatures, callCC :: ((forall b. a -> m b) -> m a) -> m a -- this is rank-3 RankNTypes implies ExistentialQuantification (among others). -- Dave Menendez <dave@zednenem.com> <http://www.eyrie.org/~zednenem/>