Daniel Waterworth <[email protected]> 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/
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