ghc-6.12.3: The GHC APISource codeContentsIndex
MonadUtils
Description
Utilities related to Monad and Applicative classes Mostly for backwards compatability.
Synopsis
class Functor f => Applicative f where
pure :: a -> f a
(<*>) :: f (a -> b) -> f a -> f b
(*>) :: f a -> f b -> f b
(<*) :: f a -> f b -> f a
(<$>) :: Functor f => (a -> b) -> f a -> f b
class Monad m => MonadFix m where
mfix :: (a -> m a) -> m a
class Monad m => MonadIO m where
liftIO :: IO a -> m a
liftIO1 :: MonadIO m => (a -> IO b) -> a -> m b
liftIO2 :: MonadIO m => (a -> b -> IO c) -> a -> b -> m c
liftIO3 :: MonadIO m => (a -> b -> c -> IO d) -> a -> b -> c -> m d
liftIO4 :: MonadIO m => (a -> b -> c -> d -> IO e) -> a -> b -> c -> d -> m e
zipWith3M :: Monad m => (a -> b -> c -> m d) -> [a] -> [b] -> [c] -> m [d]
mapAndUnzipM :: Monad m => (a -> m (b, c)) -> [a] -> m ([b], [c])
mapAndUnzip3M :: Monad m => (a -> m (b, c, d)) -> [a] -> m ([b], [c], [d])
mapAndUnzip4M :: Monad m => (a -> m (b, c, d, e)) -> [a] -> m ([b], [c], [d], [e])
mapAccumLM :: Monad m => (acc -> x -> m (acc, y)) -> acc -> [x] -> m (acc, [y])
mapSndM :: Monad m => (b -> m c) -> [(a, b)] -> m [(a, c)]
concatMapM :: Monad m => (a -> m [b]) -> [a] -> m [b]
mapMaybeM :: Monad m => (a -> m (Maybe b)) -> [a] -> m [b]
anyM :: Monad m => (a -> m Bool) -> [a] -> m Bool
allM :: Monad m => (a -> m Bool) -> [a] -> m Bool
foldlM :: Monad m => (a -> b -> m a) -> a -> [b] -> m a
foldlM_ :: Monad m => (a -> b -> m a) -> a -> [b] -> m ()
foldrM :: Monad m => (b -> a -> m a) -> a -> [b] -> m a
maybeMapM :: Monad m => (a -> m b) -> Maybe a -> m (Maybe b)
Documentation
class Functor f => Applicative f whereSource

A functor with application.

Instances should satisfy the following laws:

identity
pure id <*> v = v
composition
pure (.) <*> u <*> v <*> w = u <*> (v <*> w)
homomorphism
pure f <*> pure x = pure (f x)
interchange
u <*> pure y = pure ($ y) <*> u
ignore left value
u *> v = pure (const id) <*> u <*> v
ignore right value
u <* v = pure const <*> u <*> v

The Functor instance should satisfy

fmap f x = pure f <*> x

If f is also a Monad, define pure = return and (<*>) = ap.

Minimal complete definition: pure and <*>.

Methods
pure :: a -> f aSource
Lift a value.
(<*>) :: f (a -> b) -> f a -> f bSource
Sequential application.
(*>) :: f a -> f b -> f bSource
Sequence actions, discarding the value of the first argument.
(<*) :: f a -> f b -> f aSource
Sequence actions, discarding the value of the second argument.
show/hide Instances
(<$>) :: Functor f => (a -> b) -> f a -> f bSource
An infix synonym for fmap.
class Monad m => MonadFix m whereSource

Monads having fixed points with a 'knot-tying' semantics. Instances of MonadFix should satisfy the following laws:

purity
mfix (return . h) = return (fix h)
left shrinking (or tightening)
mfix (\x -> a >>= \y -> f x y) = a >>= \y -> mfix (\x -> f x y)
sliding
mfix (Control.Monad.liftM h . f) = Control.Monad.liftM h (mfix (f . h)), for strict h.
nesting
mfix (\x -> mfix (\y -> f x y)) = mfix (\x -> f x x)

This class is used in the translation of the recursive do notation supported by GHC and Hugs.

Methods
mfix :: (a -> m a) -> m aSource
The fixed point of a monadic computation. mfix f executes the action f only once, with the eventual output fed back as the input. Hence f should not be strict, for then mfix f would diverge.
show/hide Instances
class Monad m => MonadIO m whereSource
Methods
liftIO :: IO a -> m aSource
show/hide Instances
liftIO1 :: MonadIO m => (a -> IO b) -> a -> m bSource
Lift an IO operation with 1 argument into another monad
liftIO2 :: MonadIO m => (a -> b -> IO c) -> a -> b -> m cSource
Lift an IO operation with 2 arguments into another monad
liftIO3 :: MonadIO m => (a -> b -> c -> IO d) -> a -> b -> c -> m dSource
Lift an IO operation with 3 arguments into another monad
liftIO4 :: MonadIO m => (a -> b -> c -> d -> IO e) -> a -> b -> c -> d -> m eSource
Lift an IO operation with 4 arguments into another monad
zipWith3M :: Monad m => (a -> b -> c -> m d) -> [a] -> [b] -> [c] -> m [d]Source
mapAndUnzipM :: Monad m => (a -> m (b, c)) -> [a] -> m ([b], [c])Source
The mapAndUnzipM function maps its first argument over a list, returning the result as a pair of lists. This function is mainly used with complicated data structures or a state-transforming monad.
mapAndUnzip3M :: Monad m => (a -> m (b, c, d)) -> [a] -> m ([b], [c], [d])Source
mapAndUnzipM for triples
mapAndUnzip4M :: Monad m => (a -> m (b, c, d, e)) -> [a] -> m ([b], [c], [d], [e])Source
mapAccumLMSource
:: Monad m
=> acc -> x -> m (acc, y)combining funcction
-> accinitial state
-> [x]inputs
-> m (acc, [y])final state, outputs
Monadic version of mapAccumL
mapSndM :: Monad m => (b -> m c) -> [(a, b)] -> m [(a, c)]Source
Monadic version of mapSnd
concatMapM :: Monad m => (a -> m [b]) -> [a] -> m [b]Source
Monadic version of concatMap
mapMaybeM :: Monad m => (a -> m (Maybe b)) -> [a] -> m [b]Source
Monadic version of mapMaybe
anyM :: Monad m => (a -> m Bool) -> [a] -> m BoolSource
Monadic version of any, aborts the computation at the first True value
allM :: Monad m => (a -> m Bool) -> [a] -> m BoolSource
Monad version of all, aborts the computation at the first False value
foldlM :: Monad m => (a -> b -> m a) -> a -> [b] -> m aSource
Monadic version of foldl
foldlM_ :: Monad m => (a -> b -> m a) -> a -> [b] -> m ()Source
Monadic version of foldl that discards its result
foldrM :: Monad m => (b -> a -> m a) -> a -> [b] -> m aSource
Monadic version of foldr
maybeMapM :: Monad m => (a -> m b) -> Maybe a -> m (Maybe b)Source
Monadic version of fmap specialised for Maybe
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