Hi, Mitar wrote:
I would like to do that to remove repeating code like:
from<- newChan for<- newChan let nerve = Nerve (Axon from) (AxonAny for)
which I have to write again and again just to make types work out. Why I cannot move that into the function?
One option is to write a little library of functions which create axons and nerves: newAxon :: Impulse i => IO (Axon (Chan i) i AxonConductive) newAxon = do chan <- newChan return (Axon chan) newAxonAny :: IO (Axon (Chan i) AnyImpulse AxonConductive) newAxonAny = do chan <- newChan return (AxonAny chan) newNoAxon :: Monad m => m (Axon (Chan i) i AxonNotConductive) newNoAxon = do return NoAxon newNerve :: Monad m => m (Axon a a' b) -> m (Axon c c' d) -> m (Nerve a a' b c c' d) newNerve newFrom newFor = do from <- newFrom for <- newFor return (Nerve from for) Note that newNerve does not take Axons, but rather monadic actions which create Axons. Now, you can use something like nerve <- newNerve newAxon newAxonAny to create a concrete nerve. Tillmann PS. It might be an interesting exercise to use either liftM and liftM2 (from Control.Monad) or the (<$>) and (<*>) operators from Control.Applicative to implement these functions without do notation. PPS. Crosspost removed. I don't want to post to mailing lists which I do not read.