Haskus.Utils.Monad

Utils for Monads

Documentation

class MonadIO m => MonadInIO m where

Methods

liftWith :: (forall c. (a -> IO c) -> IO c) -> (a -> m b) -> m b

Lift with*-like functions into IO (alloca, etc.)

liftWith2 :: (forall c. (a -> b -> IO c) -> IO c) -> (a -> b -> m e) -> m e

Lift with*-like functions into IO (alloca, etc.)

Instances

MonadInIO IO

Defined in Haskus.Utils.Monad

Methods

liftWith :: (forall c. (a -> IO c) -> IO c) -> (a -> IO b) -> IO b

liftWith2 :: (forall c. (a -> b -> IO c) -> IO c) -> (a -> b -> IO e) -> IO e

MonadInIO m => MonadInIO (StateT s m)

Defined in Haskus.Utils.Monad

Methods

liftWith :: (forall c. (a -> IO c) -> IO c) -> (a -> StateT s m b) -> StateT s m b

liftWith2 :: (forall c. (a -> b -> IO c) -> IO c) -> (a -> b -> StateT s m e) -> StateT s m e

module Control.Monad

module Control.Monad.IO.Class

module Control.Monad.Trans.Class

whileM :: Monad m => m Bool -> m ()

Keep running an operation until it becomes False. As an example:

whileM $ do sleep 0.1; notM $ doesFileExist "foo.txt"
readFile "foo.txt"

If you need some state persisted between each test, use loopM.

loop :: (a -> Either a b) -> a -> b

A looping operation, where the predicate returns Left as a seed for the next loop or Right to abort the loop.

loop (\x -> if x < 10 then Left $ x * 2 else Right $ show x) 1 == "16"

loopM :: Monad m => (a -> m (Either a b)) -> a -> m b

A monadic version of loop, where the predicate returns Left as a seed for the next loop or Right to abort the loop.

whenM :: Monad m => m Bool -> m () -> m ()

Like when, but where the test can be monadic.

unlessM :: Monad m => m Bool -> m () -> m ()

Like unless, but where the test can be monadic.

ifM :: Monad m => m Bool -> m a -> m a -> m a

Like if, but where the test can be monadic.

notM :: Functor m => m Bool -> m Bool

Like not, but where the test can be monadic.

anyM :: Monad m => (a -> m Bool) -> [a] -> m Bool

A version of any lifted to a monad. Retains the short-circuiting behaviour.

anyM Just [False,True ,undefined] == Just True
anyM Just [False,False,undefined] == undefined
\(f :: Int -> Maybe Bool) xs -> anyM f xs == orM (map f xs)

allM :: Monad m => (a -> m Bool) -> [a] -> m Bool

A version of all lifted to a monad. Retains the short-circuiting behaviour.

allM Just [True,False,undefined] == Just False
allM Just [True,True ,undefined] == undefined
\(f :: Int -> Maybe Bool) xs -> anyM f xs == orM (map f xs)

orM :: Monad m => [m Bool] -> m Bool

A version of or lifted to a monad. Retains the short-circuiting behaviour.

orM [Just False,Just True ,undefined] == Just True
orM [Just False,Just False,undefined] == undefined
\xs -> Just (or xs) == orM (map Just xs)

andM :: Monad m => [m Bool] -> m Bool

A version of and lifted to a monad. Retains the short-circuiting behaviour.

andM [Just True,Just False,undefined] == Just False
andM [Just True,Just True ,undefined] == undefined
\xs -> Just (and xs) == andM (map Just xs)