Safe Haskell	Safe
Language	Haskell2010

MonadUtils

Description

Utilities related to Monad and Applicative classes Mostly for backwards compatability.

Synopsis

Documentation

class Functor f => Applicative f where Source

A functor with application, providing operations to

embed pure expressions (pure), and
sequence computations and combine their results (<*>).

A minimal complete definition must include implementations of these functions satisfying 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

The other methods have the following default definitions, which may be overridden with equivalent specialized implementations:

```
u *> v = pure (const id) <*> u <*> v
```
```
u <* v = pure const <*> u <*> v
```

As a consequence of these laws, the Functor instance for f will satisfy

```
fmap f x = pure f <*> x
```

If f is also a Monad, it should satisfy

```
pure = return
```
```
(<*>) = ap
```

(which implies that pure and <*> satisfy the applicative functor laws).

Minimal complete definition

pure, (<*>)

Methods

pure :: a -> f a Source

Lift a value.

(<*>) :: f (a -> b) -> f a -> f b infixl 4 Source

Sequential application.

(*>) :: f a -> f b -> f b infixl 4 Source

Sequence actions, discarding the value of the first argument.

(<*) :: f a -> f b -> f a infixl 4 Source

Sequence actions, discarding the value of the second argument.

Instances

Applicative []
Applicative IO
Applicative Q
Applicative Id
Applicative P
Applicative ZipList
Applicative STM
Applicative First
Applicative Last
Applicative ReadPrec
Applicative ReadP
Applicative Maybe
Applicative Seq
Applicative VM
Applicative SimpleUniqueMonad
Applicative Pair
Applicative UniqSM
Applicative P
Applicative OccCheckResult
Applicative LlvmM
Applicative NatM
Applicative FCode
Applicative CmmParse
Applicative Hsc
Applicative Ghc
Applicative CompPipeline
Applicative TcPluginM
Applicative CoreM
Applicative VM
Applicative SimplM
Applicative TcS
Applicative CpsRn
Applicative ((->) a)
Applicative (Either e)
Monoid a => Applicative ((,) a)
Applicative (ST s)
Applicative (StateL s)
Applicative (StateR s)
Applicative (ST s)
Monoid m => Applicative (Const m)
Monad m => Applicative (WrappedMonad m)
Arrow a => Applicative (ArrowMonad a)
Applicative (Proxy *)
Applicative (State s)
Monad m => Applicative (CheckingFuelMonad m)
Monad m => Applicative (InfiniteFuelMonad m)
Monad m => Applicative (UniqueMonadT m)
Applicative (MaybeErr err)
(Monad m, Functor m) => Applicative (MaybeT m)
Applicative (State s)
Applicative (CmdLineP s)
Monad m => Applicative (EwM m)
Applicative (IOEnv m)
Applicative (RegM freeRegs)
Applicative m => Applicative (GhcT m)
Arrow a => Applicative (WrappedArrow a b)
Applicative f => Applicative (Alt * f)
(Functor m, Monad m) => Applicative (StateT s m)
Monad m => Applicative (Stream m a)
Typeable ((* -> *) -> Constraint) Applicative

(<$>) :: Functor f => (a -> b) -> f a -> f b infixl 4 Source

An infix synonym for fmap.

Examples

Convert from a Maybe Int to a Maybe String using show:

>>> show <$> Nothing
Nothing
>>> show <$> Just 3
Just "3"

Convert from an Either Int Int to an Either Int String using show:

>>> show <$> Left 17
Left 17
>>> show <$> Right 17
Right "17"

Double each element of a list:

>>> (*2) <$> [1,2,3]
[2,4,6]

Apply even to the second element of a pair:

>>> even <$> (2,2)
(2,True)

class Monad m => MonadFix m where Source

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 (liftM h . f) = 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 a Source

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.

Instances

MonadFix []
MonadFix IO
MonadFix Maybe
MonadFix UniqSM
MonadFix Ghc
MonadFix ((->) r)
MonadFix (Either e)
MonadFix (ST s)
MonadFix (ST s)
MonadFix m => MonadFix (StateT s m)

class Monad m => MonadIO m where Source

Monads in which IO computations may be embedded. Any monad built by applying a sequence of monad transformers to the IO monad will be an instance of this class.

Instances should satisfy the following laws, which state that liftIO is a transformer of monads:

```
liftIO . return = return
```

liftIO (m >>= f) = liftIO m >>= (liftIO . f)

Methods

liftIO :: IO a -> m a Source

Lift a computation from the IO monad.

Instances

MonadIO IO
MonadIO Hsc
MonadIO Ghc
MonadIO CompPipeline
MonadIO CoreM
MonadIO VM
MonadIO SimplM
MonadIO (IOEnv env)
MonadIO m => MonadIO (GhcT m)
MonadIO m => MonadIO (StateT s m)
Typeable ((* -> *) -> Constraint) MonadIO

liftIO1 :: MonadIO m => (a -> IO b) -> a -> m b Source

Lift an IO operation with 1 argument into another monad

liftIO2 :: MonadIO m => (a -> b -> IO c) -> a -> b -> m c Source

Lift an IO operation with 2 arguments into another monad

liftIO3 :: MonadIO m => (a -> b -> c -> IO d) -> a -> b -> c -> m d Source

Lift an IO operation with 3 arguments into another monad

liftIO4 :: MonadIO m => (a -> b -> c -> d -> IO e) -> a -> b -> c -> d -> m e Source

Lift an IO operation with 4 arguments into another monad

zipWith3M :: Monad m => (a -> b -> c -> m d) -> [a] -> [b] -> [c] -> m [d] Source

zipWith3M_ :: Monad m => (a -> b -> c -> m d) -> [a] -> [b] -> [c] -> m () Source

zipWithAndUnzipM :: Monad m => (a -> b -> m (c, d)) -> [a] -> [b] -> m ([c], [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

mapAccumLM Source

Arguments

:: Monad m
=> (acc -> x -> m (acc, y))	combining funcction
-> acc	initial 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

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

Monadic version of fmap

fmapEitherM :: Monad m => (a -> m b) -> (c -> m d) -> Either a c -> m (Either b d) Source

Monadic version of fmap

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

Monadic version of any, aborts the computation at the first True value

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

Monad version of all, aborts the computation at the first False value

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

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 a Source

Monadic version of foldr

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

Monadic version of fmap specialised for Maybe

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

Monadic version of when, taking the condition in the monad