On Mon, 13 Aug 2012, Johan Holmquist <holmi...@gmail.com> wrote:
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.
On Aug 12, 2012 10:36 AM, "Daniel Trstenjak" <daniel.trsten...@gmail.com>
wrote:
Does Haskell have a word for "existential type" declaration? I
have the impression, and this must be wrong, that "forall" does
double duty, that is, it declares a "for all" in some sense like
the usual "for all" of the Lower Predicate Calculus, perhaps the
"for all" of system F, or something near it.
oo--JS.
Hi Oleg,
On Sat, Aug 11, 2012 at 08:14:47AM -0000, o...@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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