coroutine forever

forever.hs

module Main where
import Control.Monad.State
import Control.Monad.Coroutine
import Control.Monad.Coroutine.SuspensionFunctors

crst :: Coroutine (Yield Int) (StateT Int IO) Int
crst = do v<-lift get;yield v;lift(modify(+1));liftIO(putStr "動く">>print(v*10)); return (v*10)

runT :: MonadIO m=>Coroutine (Yield Int) m Int -> m Int
runT c = resume c>>=g where
  g(Right e) = liftIO(putStr "foreverなら動かない">>print e)>> return e
  g(Left(Yield e c))=do
    liftIO(print e)
    if e >= 3 then return e else runT c

main = do
  evalStateT (runT crst) 1
  evalStateT (runT $ forever crst) 1

1
動く10
foreverなら動かない10
1
動く10
2
動く20
3