Safe Haskell	Safe-Inferred

Control.Monad.Loops

Description

A collection of loop operators for use in monads (mostly in stateful ones).

There is a general naming pattern for many of these: Functions with names ending in _ discard the results of the loop body as in the standard Prelude mapM functions.

Functions with names ending in ' collect their results into MonadPlus containers. Note that any short-circuit effect that those types' MonadPlus instances may provide in a lazy context (such as the instance for Maybe) will _not_ cause execution to short-circuit in these loops.

Functions with names ending in neither of those will generally return just plain old lists.

Synopsis

Documentation

forkMapM :: (a -> IO b) -> [a] -> IO [Either SomeException b]

Like mapM, but run all the actions in parallel threads, collecting up the results and returning them all. Does not return until all actions finish.

forkMapM_ :: (a -> IO b) -> [a] -> IO [Maybe SomeException]

like forkMapM but without bothering to keep the return values

forkMapM__ :: (a -> IO b) -> [a] -> IO ()

like forkMapM_ but not even bothering to track success or failure of the child threads. Still waits for them all though.

whileM :: Monad m => m Bool -> m a -> m [a]

Execute an action repeatedly as long as the given boolean expression returns True. The condition is evaluated before the loop body. Collects the results into a list.

whileM' :: (Monad m, MonadPlus f) => m Bool -> m a -> m (f a)

Execute an action repeatedly as long as the given boolean expression returns True. The condition is evaluated before the loop body. Collects the results into an arbitrary MonadPlus value.

whileM_ :: Monad m => m Bool -> m a -> m ()

Execute an action repeatedly as long as the given boolean expression returns True. The condition is evaluated before the loop body. Discards results.

iterateWhile :: Monad m => (a -> Bool) -> m a -> m a

Execute an action repeatedly until its result fails to satisfy a predicate, and return that result (discarding all others).

iterateM_ :: Monad m => (a -> m a) -> a -> m b

Execute an action forever, feeding the result of each execution as the input to the next.

untilM :: Monad m => m a -> m Bool -> m [a]

Execute an action repeatedly until the condition expression returns True. The condition is evaluated after the loop body. Collects results into a list. Parameters are arranged for infix usage. eg. do {...} untilM_ ...

untilM' :: (Monad m, MonadPlus f) => m a -> m Bool -> m (f a)

Execute an action repeatedly until the condition expression returns True. The condition is evaluated after the loop body. Collects results into a MonadPlus value. Parameters are arranged for infix usage. eg. do {...} untilM_ ...

untilM_ :: Monad m => m a -> m Bool -> m ()

Execute an action repeatedly until the condition expression returns True. The condition is evaluated after the loop body. Discards results. Parameters are arranged for infix usage. eg. do {...} untilM_ ...

iterateUntil :: Monad m => (a -> Bool) -> m a -> m a

Execute an action repeatedly until its result satisfies a predicate, and return that result (discarding all others).

whileJust :: Monad m => m (Maybe a) -> (a -> m b) -> m [b]

As long as the supplied Maybe expression returns Just _, the loop body will be called and passed the value contained in the Just. Results are collected into a list.

whileJust' :: (Monad m, MonadPlus f) => m (Maybe a) -> (a -> m b) -> m (f b)

As long as the supplied Maybe expression returns Just _, the loop body will be called and passed the value contained in the Just. Results are collected into an arbitrary MonadPlus container.

whileJust_ :: Monad m => m (Maybe a) -> (a -> m b) -> m ()

As long as the supplied Maybe expression returns Just _, the loop body will be called and passed the value contained in the Just. Results are discarded.

untilJust :: Monad m => m (Maybe a) -> m a

Run the supplied Maybe computation repeatedly until it returns a value. Returns that value.

unfoldM :: Monad m => m (Maybe a) -> m [a]

The supplied Maybe expression will be repeatedly called until it returns Nothing. All values returned are collected into a list.

unfoldM' :: (Monad m, MonadPlus f) => m (Maybe a) -> m (f a)

The supplied Maybe expression will be repeatedly called until it returns Nothing. All values returned are collected into an arbitrary MonadPlus thing.

unfoldM_ :: Monad m => m (Maybe a) -> m ()

The supplied Maybe expression will be repeatedly called until it returns Nothing. All values returned are discarded.

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

Repeatedly evaluates the second argument until the value satisfies the given predicate, and returns a list of all values that satisfied the predicate. Discards the final one (which failed the predicate).

unfoldWhileM' :: (Monad m, MonadPlus f) => (a -> Bool) -> m a -> m (f a)

Repeatedly evaluates the second argument until the value satisfies the given predicate, and returns a MonadPlus collection of all values that satisfied the predicate. Discards the final one (which failed the predicate).

unfoldrM :: Monad m => (a -> m (Maybe (b, a))) -> a -> m [b]

See unfoldr. This is a monad-friendly version of that.

unfoldrM' :: (Monad m, MonadPlus f) => (a -> m (Maybe (b, a))) -> a -> m (f b)

See unfoldr. This is a monad-friendly version of that, with a twist. Rather than returning a list, it returns any MonadPlus type of your choice.

concatM :: Monad m => [a -> m a] -> a -> m a

Compose a list of monadic actions into one action. Composes using (>=>) - that is, the output of each action is fed to the input of the one after it in the list.

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

short-circuit and for values of type Monad m => m Bool

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

short-circuit or for values of type Monad m => m Bool

anyPM :: Monad m => [a -> m Bool] -> a -> m Bool

short-circuit any with a list of "monadic predicates". Tests the value presented against each predicate in turn until one passes, then returns True without any further processing. If none passes, returns False.

allPM :: Monad m => [a -> m Bool] -> a -> m Bool

short-circuit all with a list of "monadic predicates". Tests the value presented against each predicate in turn until one fails, then returns False. if none fail, returns True.

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

short-circuit any with a "monadic predicate".

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

short-circuit all with a "monadic predicate".

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

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

like dropWhileM but trims both ends of the list.

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

return the first value from a list, if any, satisfying the given predicate.

minimaOnByM :: Monad m => (a -> m b) -> (b -> b -> m Ordering) -> [a] -> m [a]

maximaOnByM :: Monad m => (a -> m b) -> (b -> b -> m Ordering) -> [a] -> m [a]

minimaByM :: Monad m => (a -> a -> m Ordering) -> [a] -> m [a]