David Menendez wrote:
On Thu, Dec 11, 2008 at 1:48 PM, Andrew Coppin
<andrewcop...@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).
So how is
foo :: ((forall b. a -> m b) -> m a) -> m a
different from
bar :: forall b. ((a -> m b) -> m a) -> m a
then?
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