Safe Haskell | Safe |
---|---|

Language | Haskell2010 |

Extra functions for Control.Monad. These functions provide looping, list operations and booleans. If you need a wider selection of monad loops and list generalisations, see monad-loops.

## Synopsis

- module Control.Monad
- whenJust :: Applicative m => Maybe a -> (a -> m ()) -> m ()
- whenJustM :: Monad m => m (Maybe a) -> (a -> m ()) -> m ()
- whenMaybe :: Applicative m => Bool -> m a -> m (Maybe a)
- whenMaybeM :: Monad m => m Bool -> m a -> m (Maybe a)
- unit :: m () -> m ()
- maybeM :: Monad m => m b -> (a -> m b) -> m (Maybe a) -> m b
- fromMaybeM :: Monad m => m a -> m (Maybe a) -> m a
- eitherM :: Monad m => (a -> m c) -> (b -> m c) -> m (Either a b) -> m c
- loop :: (a -> Either a b) -> a -> b
- loopM :: Monad m => (a -> m (Either a b)) -> a -> m b
- whileM :: Monad m => m Bool -> m ()
- whileJustM :: (Monad m, Monoid a) => m (Maybe a) -> m a
- untilJustM :: Monad m => m (Maybe a) -> m a
- partitionM :: Monad m => (a -> m Bool) -> [a] -> m ([a], [a])
- concatMapM :: Monad m => (a -> m [b]) -> [a] -> m [b]
- concatForM :: Monad m => [a] -> (a -> m [b]) -> m [b]
- mconcatMapM :: (Monad m, Monoid b) => (a -> m b) -> [a] -> m b
- mapMaybeM :: Monad m => (a -> m (Maybe b)) -> [a] -> m [b]
- findM :: Monad m => (a -> m Bool) -> [a] -> m (Maybe a)
- firstJustM :: Monad m => (a -> m (Maybe b)) -> [a] -> m (Maybe b)
- fold1M :: (Partial, Monad m) => (a -> a -> m a) -> [a] -> m a
- fold1M_ :: (Partial, Monad m) => (a -> a -> m a) -> [a] -> m ()
- whenM :: Monad m => m Bool -> m () -> m ()
- unlessM :: Monad m => m Bool -> m () -> m ()
- ifM :: Monad m => m Bool -> m a -> m a -> m a
- notM :: Functor m => m Bool -> m Bool
- (||^) :: Monad m => m Bool -> m Bool -> m Bool
- (&&^) :: Monad m => m Bool -> m Bool -> m Bool
- orM :: Monad m => [m Bool] -> m Bool
- andM :: Monad m => [m Bool] -> m Bool
- anyM :: Monad m => (a -> m Bool) -> [a] -> m Bool
- allM :: Monad m => (a -> m Bool) -> [a] -> m Bool

# Documentation

module Control.Monad

whenJust :: Applicative m => Maybe a -> (a -> m ()) -> m () Source #

whenJustM :: Monad m => m (Maybe a) -> (a -> m ()) -> m () Source #

Like `whenJust`

, but where the test can be monadic.

whenMaybeM :: Monad m => m Bool -> m a -> m (Maybe a) Source #

Like `whenMaybe`

, but where the test can be monadic.

The identity function which requires the inner argument to be `()`

. Useful for functions
with overloaded return types.

\(x :: Maybe ()) -> unit x == x

maybeM :: Monad m => m b -> (a -> m b) -> m (Maybe a) -> m b Source #

Monadic generalisation of `maybe`

.

eitherM :: Monad m => (a -> m c) -> (b -> m c) -> m (Either a b) -> m c Source #

Monadic generalisation of `either`

.

# Loops

untilJustM :: Monad m => m (Maybe a) -> m a Source #

# Lists

partitionM :: Monad m => (a -> m Bool) -> [a] -> m ([a], [a]) Source #

A version of `partition`

that works with a monadic predicate.

partitionM (Just . even) [1,2,3] == Just ([2], [1,3]) partitionM (const Nothing) [1,2,3] == Nothing

concatMapM :: Monad m => (a -> m [b]) -> [a] -> m [b] Source #

A version of `concatMap`

that works with a monadic predicate.

concatForM :: Monad m => [a] -> (a -> m [b]) -> m [b] Source #

Like `concatMapM`

, but has its arguments flipped, so can be used
instead of the common `fmap concat $ forM`

pattern.

mconcatMapM :: (Monad m, Monoid b) => (a -> m b) -> [a] -> m b Source #

A version of `mconcatMap`

that works with a monadic predicate.

mapMaybeM :: Monad m => (a -> m (Maybe b)) -> [a] -> m [b] Source #

A version of `mapMaybe`

that works with a monadic predicate.

findM :: Monad m => (a -> m Bool) -> [a] -> m (Maybe a) Source #

Like `find`

, but where the test can be monadic.

findM (Just . isUpper) "teST" == Just (Just 'S') findM (Just . isUpper) "test" == Just Nothing findM (Just . const True) ["x",undefined] == Just (Just "x")

firstJustM :: Monad m => (a -> m (Maybe b)) -> [a] -> m (Maybe b) Source #

Like `findM`

, but also allows you to compute some additional information in the predicate.

fold1M :: (Partial, Monad m) => (a -> a -> m a) -> [a] -> m a Source #

A variant of `foldM`

that has no base case, and thus may only be applied to non-empty lists.

fold1M (\x y -> Just x) [] == undefined fold1M (\x y -> Just $ x + y) [1, 2, 3] == Just 6

fold1M_ :: (Partial, Monad m) => (a -> a -> m a) -> [a] -> m () Source #

Like `fold1M`

but discards the result.

# Booleans

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

Like `unless`

, but where the test can be monadic.

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

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 Source #

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)