Twan van Laarhoven wrote:
For reference, here the full signature of the core combinators:
data Event a
data Behavior a
instance Functor Behavior
instance Applicative Behavior
instance Functor Event
instance Monoid (Event a)
filter :: (a -> Bool) -> Event a -> Event a
apply :: Behavior (a -> b) -> Event a -> Event b
accumB :: a -> Event (a -> a) -> Behavior a
The apply and accumB functions are harder. Is the Behavior
implementation for the model really different from the one of the
implementation, which seems to be {initial::a, changes::Event a}? If
not, you could just generalize that type by making the event type a
parameter
data GenBehavior e a = GB a (E a)
If this is not the case,
I have changed the both implementations completely, so this no longer an
option.
then instead of MPTCs you could also try type
families,
class ... => FRP event where
data Behavior event
apply :: Behavior event (a -> b) -> event a -> event b
accumB :: a -> event (a -> a) -> Behavior event a
I don't know whether this is any better than the MPTC approach, though.
Data type families have the advantage that I don't run into problems
with ambiguity. The following seems sensible to me:
class (Functor (Event f), Functor (Behavior f),
Applicative (Behavior f)) => FRP f where
apply :: Behavior f (a -> b) -> Event f a -> Event f b
...
where f is simply a dummy variable to index different FRP implementations.
The problem with this is that I need the FlexibleContexts extension to
do that. There goes Haskell2010 compatibility.
Best regards,
Heinrich Apfelmus
--
http://apfelmus.nfshost.com
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
