That pattern looks so familiar. :) Existential types seem to fit in to the type system really well so I never got why it is not part of the standard.
Hi Oleg,
On Sat, Aug 11, 2012 at 08:14:47AM -0000, oleg@okmij.org wrote:
> I'd like to point out that the only operation we can do on the first
> argument of MkFoo is to show to it. This is all we can ever do:
> we have no idea of its type but we know we can show it and get a
> String. Why not to apply show to start with (it won't be evaluated
> until required anyway)?
It's only a test case. The real thing is for a game and will be
something like:
class EntityT e where
update :: e -> e
render :: e -> IO ()
handleEvent :: e -> Event -> e
getBound :: e -> Maybe Bound
data Entity = forall e. (EntityT e) => Entity e
data Level = Level {
entities = [Entity],
...
}
Greetings,
Daniel
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