Safe Haskell	Safe
Language	Haskell98

Control.Monad.ListT

Description

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.Funcs (repeatM)
import Data.List.Class (execute, scanl, takeWhile, mapL)
import Prelude hiding (scanl, takeWhile)

main =
    execute . mapL print .
    scanl (+) 0 .
    fmap (fst . head) .
    takeWhile (not . null) .
    fmap reads $ repeatM getLine

Note: The transformers package also has a ListT type, which oddly enough it is not a list monad transformer. This module was deliberately named differently from transformers's module.

Documentation

newtype ListT m a Source #

Constructors

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

Instances

MonadTrans ListT Source #
Methods lift :: Monad m => m a -> ListT m a #
Monad m => Monad (ListT m) Source #
Methods (>>=) :: ListT m a -> (a -> ListT m b) -> ListT m b # (>>) :: ListT m a -> ListT m b -> ListT m b # return :: a -> ListT m a # fail :: String -> ListT m a #
Monad m => Functor (ListT m) Source #
Methods fmap :: (a -> b) -> ListT m a -> ListT m b # (<$) :: a -> ListT m b -> ListT m a #
Monad m => Applicative (ListT m) Source #
Methods pure :: a -> ListT m a # (<>) :: ListT m (a -> b) -> ListT m a -> ListT m b # (>) :: ListT m a -> ListT m b -> ListT m b # (<*) :: ListT m a -> ListT m b -> ListT m a #
MonadIO m => MonadIO (ListT m) Source #
Methods liftIO :: IO a -> ListT m a #
Monad m => Alternative (ListT m) Source #
Methods empty :: ListT m a # (<\|>) :: ListT m a -> ListT m a -> ListT m a # some :: ListT m a -> ListT m [a] # many :: ListT m a -> ListT m [a] #
Monad m => MonadPlus (ListT m) Source #
Methods mzero :: ListT m a # mplus :: ListT m a -> ListT m a -> ListT m a #
Monad m => List (ListT m) Source #
Associated Types type ItemM (ListT m :: * -> ) :: -> * Source # Methods runList :: ListT m a -> ItemM (ListT m) (ListItem (ListT m) a) Source # joinL :: ItemM (ListT m) (ListT m a) -> ListT m a Source # cons :: a -> ListT m a -> ListT m a Source #
Eq (m (ListItem (ListT m) a)) => Eq (ListT m a) Source #
Methods (==) :: ListT m a -> ListT m a -> Bool # (/=) :: ListT m a -> ListT m a -> Bool #
Ord (m (ListItem (ListT m) a)) => Ord (ListT m a) Source #
Methods compare :: ListT m a -> ListT m a -> Ordering # (<) :: ListT m a -> ListT m a -> Bool # (<=) :: ListT m a -> ListT m a -> Bool # (>) :: ListT m a -> ListT m a -> Bool # (>=) :: ListT m a -> ListT m a -> Bool # max :: ListT m a -> ListT m a -> ListT m a # min :: ListT m a -> ListT m a -> ListT m a #
Read (m (ListItem (ListT m) a)) => Read (ListT m a) Source #
Methods readsPrec :: Int -> ReadS (ListT m a) # readList :: ReadS [ListT m a] # readPrec :: ReadPrec (ListT m a) # readListPrec :: ReadPrec [ListT m a] #
Show (m (ListItem (ListT m) a)) => Show (ListT m a) Source #
Methods showsPrec :: Int -> ListT m a -> ShowS # show :: ListT m a -> String # showList :: [ListT m a] -> ShowS #
Monad m => Monoid (ListT m a) Source #
Methods mempty :: ListT m a # mappend :: ListT m a -> ListT m a -> ListT m a # mconcat :: [ListT m a] -> ListT m a #
type ItemM (ListT m) Source #
type ItemM (ListT m) = m