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.

- forkMapM :: (a -> IO b) -> [a] -> IO [Either SomeException b]
- forkMapM_ :: (a -> IO b) -> [a] -> IO [Maybe SomeException]
- forkMapM__ :: (a -> IO b) -> [a] -> IO ()
- whileM :: Monad m => m Bool -> m a -> m [a]
- whileM' :: (Monad m, MonadPlus f) => m Bool -> m a -> m (f a)
- whileM_ :: Monad m => m Bool -> m a -> m ()
- iterateWhile :: Monad m => (a -> Bool) -> m a -> m a
- untilM :: Monad m => m a -> m Bool -> m [a]
- untilM' :: (Monad m, MonadPlus f) => m a -> m Bool -> m (f a)
- untilM_ :: Monad m => m a -> m Bool -> m ()
- iterateUntil :: Monad m => (a -> Bool) -> m a -> m a
- whileJust :: Monad m => m (Maybe a) -> (a -> m b) -> m [b]
- whileJust' :: (Monad m, MonadPlus f) => m (Maybe a) -> (a -> m b) -> m (f b)
- whileJust_ :: Monad m => m (Maybe a) -> (a -> m b) -> m ()
- untilJust :: Monad m => m (Maybe a) -> m a
- unfoldM :: Monad m => m (Maybe a) -> m [a]
- unfoldM' :: (Monad m, MonadPlus f) => m (Maybe a) -> m (f a)
- unfoldM_ :: Monad m => m (Maybe a) -> m ()
- unfoldWhileM :: Monad m => (a -> Bool) -> m a -> m [a]
- unfoldWhileM' :: (Monad m, MonadPlus f) => (a -> Bool) -> m a -> m (f a)
- unfoldrM :: Monad m => (a -> m (Maybe (b, a))) -> a -> m [b]
- unfoldrM' :: (Monad m, MonadPlus f) => (a -> m (Maybe (b, a))) -> a -> m (f b)
- concatM :: Monad m => [a -> m a] -> a -> m a
- andM :: Monad m => [m Bool] -> m Bool
- orM :: Monad m => [m Bool] -> m Bool
- anyPM :: Monad m => [a -> m Bool] -> a -> m Bool
- allPM :: Monad m => [a -> m Bool] -> a -> m Bool
- anyM :: Monad m => (a -> m Bool) -> [a] -> m Bool
- allM :: Monad m => (a -> m Bool) -> [a] -> m Bool
- dropWhileM :: Monad m => (a -> m Bool) -> [a] -> m [a]
- trimM :: Monad m => (a -> m Bool) -> [a] -> m [a]
- firstM :: Monad m => (a -> m Bool) -> [a] -> m (Maybe a)
- atomLoop :: STM a -> IO ()
- forkAtomLoop :: STM a -> IO ThreadId
- waitFor :: (a -> Bool) -> STM a -> STM a
- waitForTrue :: STM Bool -> STM ()
- waitForJust :: STM (Maybe a) -> STM a
- waitForEvent :: (a -> Bool) -> TChan a -> STM a

# Documentation

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

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]Source

like `forkMapM`

but without bothering to keep the return values

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

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]Source

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)Source

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 ()Source

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 aSource

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

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

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 => m a -> m Bool -> m ()Source

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 aSource

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

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

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

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

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

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

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)Source

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]Source

See `Data.List.unfoldr`

. This is a monad-friendly version of that.

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

See `Data.List.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 aSource

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.

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

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 BoolSource

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 BoolSource

short-circuit `any`

with a "monadic predicate".

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

short-circuit `all`

with a "monadic predicate".

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

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

like `dropWhileM`

but trims both ends of the list.

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

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

waitFor :: (a -> Bool) -> STM a -> STM aSource

`retry`

until the given condition is true of
the given value. Then return the value that satisfied the condition.

waitForJust :: STM (Maybe a) -> STM aSource