Version 2 (modified by blamario, 4 years ago) |
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# Package monad-coroutine

This library, implemented by the `Control.Monad.Coroutine` module, provides a limited coroutine functionality in Haskell. The centerpiece of the approach is the monad transformer `Coroutine`, which transforms an arbitrary monadic computation into a suspendable and resumable one. The basic definition is simple:

newtype Coroutine s m r = Coroutine {resume :: m (Either (s (Coroutine s m r)) r)} instance (Functor s, Monad m) => Monad (Coroutine s m) where return = Coroutine . return . Right t >>= f = Coroutine (resume t >>= either (return . Left . fmap (>>= f)) (resume . f))

The Coroutine transformer type is parameterized by a functor. The functor in question wraps the resumption of a suspended coroutine, and it can carry other information as well. Module `Control.Monad.Coroutine.SuspensionFunctors` exports some useful functors, one of which is `Yield`:

data Yield x y = Yield x y instance Functor (Yield x) where fmap f (Yield x y) = Yield x (f y)