I must admit, I haven't looked into arrows in a great deal of detail, perhaps I should.
Daniel 2011/12/22 Ertugrul Söylemez <e...@ertes.de>: > Daniel Waterworth <da.waterwo...@gmail.com> wrote: > >> I made this simple state machine combinator library today. I think it >> works as a simple example of a good use for GADTs. >> >> https://gist.github.com/1507107 > > Aren't your examples all special cases of the generic automaton arrow? > There are two ways to represent it, both with their advantages and > disadvantages: > > newtype Auto a b = Auto (a -> (b, Auto a b)) > > countFrom :: Int -> Auto a Int > countFrom n = Auto (\_ -> (n, countFrom (succ n))) > > or: > > data Auto a b = forall s. Auto s ((a, s) -> (b, s)) > > countFrom :: Int -> Auto a Int > countFrom n0 = Auto n0 (\(_, s) -> (s, succ s)) > > These state machines have local state and can be composed using > applicative and arrow interfaces: > > liftA2 (+) (countFrom 3) (countFrom 5) > > proc x -> do > n1 <- countFrom 10 -< () > n2 <- someOtherMachine -< x > anotherMachine -< n1 + n2 > > > Greets, > Ertugrul > > > -- > nightmare = unsafePerformIO (getWrongWife >>= sex) > http://ertes.de/ > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
