Control.Monad.ListT

A list monad transformer / a monadic list.

Monadic list example: A program which reads numbers from the user and accumulates them.

 import Control.Monad.ListT (ListT)
 import Data.List.Class (execute, joinM, repeat, scanl, takeWhile)
 import Prelude hiding (repeat, scanl, takeWhile)

 main =
   execute . joinM . fmap print .
   scanl (+) 0 .
   fmap (fst . head) .
   takeWhile (not . null) .
   fmap reads .
   joinM $ (repeat getLine :: ListT IO (IO String))

Documentation

data ListItem l a

Constructors

Nil

Cons

Fields

headL :: a

tailL :: l a

newtype ListT m a

Constructors

ListT

Fields

runListT :: m (ListItem (ListT m) a)

Instances

MonadTrans ListT

MonadReader s m => MonadReader s (ListT m)

MonadState s m => MonadState s (ListT m)

MonadError e m => MonadError e (ListT m)

Monad m => Monad (ListT m)

Monad m => Functor (ListT m)

Monad m => MonadPlus (ListT m)

Monad m => Applicative (ListT m)

MonadIO m => MonadIO (ListT m)

Monad m => List (ListT m)

Monad m => Monoid (ListT m a)

foldrListT :: Monad m => (a -> m b -> m b) -> m b -> ListT m a -> m b

foldr for ListT