On Mon, Jan 5, 2009 at 10:09 AM, Peter Verswyvelen
Classic FRP ("CFRP", like Fran, FAL, Reactive, Grapefruit?...) exposes signals as first class values.
Arrow based FRP ("AFRP", like Fruit, Yampa...) hides signals as first class values; instead the signal transformers are the first class values.
Can I conclude that it would theoretically be possible to translate an AFRP function into a CFRP function? I.e. is AFRP a subset of CFRP?
Why don't you check yourself? AFRP, if I recall correctly, has Arrow and ArrowLoop. So the combinators we need follow: Using a ~> b as shorthand for Behavior a -> Behavior b. -- From Arrow arr :: (a -> b) -> (a ~> b) first :: (a ~> b) -> ((a,c) ~> (b,c)) (>>>) :: (a ~> b) -> (b ~> c) -> (a ~> c) arr = fmap first f ac = liftA2 (,) (f (fst <$> ac)) (snd <$> ac) (>>>) = (>>>) -- From ArrowLoop loop :: ((a,c) ~> (b,c)) -> (a ~> b) loop f a = let bc = f (liftA2 (,) a (snd <$> bc)) in fst <$> bc So that's a positive on all the arrow combinators. You have to check the supplied primitives, too, such as integral and pswitch. Once you do that, you could even implement a ClassicFRP arrow and use that instead of the Yampa arrow, so the client code wouldn't need to be changed at all. What I have just described is the ideal situation. Here are some of the practicalities you might run into: * AFRP models events as signals of Maybe. Semantically speaking, signals of Maybe don't have nice eventy properties, such as discrete occurrences, so you might have some difficulty translating between the two. I'm currently exploring an arrow model that accounts for events properly, but that probably doesn't help you. * The above "loop" combinator is key to eliminating quadratic behavior in certain classic FRP situations, and I believe the reason arrows were explored to begin with. See "Plugging a Space Leak with an Arrow" by Hudak and Liu[1] for more. In Fran-like systems, there is another fix for this leak, in exchange for loss of perfect reactivity (making a "discrete memo table" of sorts). [1] www.cs.yale.edu/~hl293/download/*leak*.pdfhttp://www.cs.yale.edu/%7Ehl293/download/leak.pdf
Thanks, Peter _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe