Safe Haskell	Safe
Language	Haskell2010

MonadUtils

Description

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

Synopsis

class Functor f => Applicative (f :: Type -> Type) where
- pure :: a -> f a
- (<*>) :: f (a -> b) -> f a -> f b
- liftA2 :: (a -> b -> c) -> f a -> f b -> f c
- (*>) :: 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 :: Type -> Type) where
- mfix :: (a -> m a) -> m a
class Monad m => MonadIO (m :: Type -> Type) where
- liftIO :: IO a -> m a
zipWith3M :: Monad m => (a -> b -> c -> m d) -> [a] -> [b] -> [c] -> m [d]
zipWith3M_ :: Monad m => (a -> b -> c -> m d) -> [a] -> [b] -> [c] -> m ()
zipWith4M :: Monad m => (a -> b -> c -> d -> m e) -> [a] -> [b] -> [c] -> [d] -> m [e]
zipWithAndUnzipM :: Monad m => (a -> b -> m (c, d)) -> [a] -> [b] -> m ([c], [d])
mapAndUnzipM :: Applicative 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])
mapAndUnzip5M :: Monad m => (a -> m (b, c, d, e, f)) -> [a] -> m ([b], [c], [d], [e], [f])
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 :: Applicative m => (a -> m (Maybe b)) -> [a] -> m [b]
fmapMaybeM :: Monad m => (a -> m b) -> Maybe a -> m (Maybe b)
fmapEitherM :: Monad m => (a -> m b) -> (c -> m d) -> Either a c -> m (Either b d)
anyM :: Monad m => (a -> m Bool) -> [a] -> m Bool
allM :: Monad m => (a -> m Bool) -> [a] -> m Bool
orM :: Monad m => m Bool -> m Bool -> m Bool
foldlM :: (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m b
foldlM_ :: (Monad m, Foldable t) => (a -> b -> m a) -> a -> t b -> m ()
foldrM :: (Foldable t, Monad m) => (a -> b -> m b) -> b -> t a -> m b
maybeMapM :: Monad m => (a -> m b) -> Maybe a -> m (Maybe b)
whenM :: Monad m => m Bool -> m () -> m ()
unlessM :: Monad m => m Bool -> m () -> m ()
filterOutM :: Applicative m => (a -> m Bool) -> [a] -> m [a]

Documentation

class Functor f => Applicative (f :: Type -> Type) where #

A functor with application, providing operations to

embed pure expressions (pure), and
sequence computations and combine their results (<*> and liftA2).

A minimal complete definition must include implementations of pure and of either <*> or liftA2. If it defines both, then they must behave the same as their default definitions:

(<*>) = liftA2 id

liftA2 f x y = f <$> x <*> y

Further, any definition must satisfy the following:

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 = (id <$ u) <*> v
```
```
u <* v = liftA2 const u v
```

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

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

It may be useful to note that supposing

forall x y. p (q x y) = f x . g y

it follows from the above that

liftA2 p (liftA2 q u v) = liftA2 f u . liftA2 g v

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, ((<*>) | liftA2)

Methods

pure :: a -> f a #

Lift a value.

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

Sequential application.

A few functors support an implementation of <*> that is more efficient than the default one.

liftA2 :: (a -> b -> c) -> f a -> f b -> f c #

Lift a binary function to actions.

Some functors support an implementation of liftA2 that is more efficient than the default one. In particular, if fmap is an expensive operation, it is likely better to use liftA2 than to fmap over the structure and then use <*>.

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

Sequence actions, discarding the value of the first argument.

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

Sequence actions, discarding the value of the second argument.

Instances

Applicative []	Since: base-2.1
Instance details Defined in GHC.Base Methods pure :: a -> [a] # (<>) :: [a -> b] -> [a] -> [b] # liftA2 :: (a -> b -> c) -> [a] -> [b] -> [c] # (>) :: [a] -> [b] -> [b] # (<*) :: [a] -> [b] -> [a] #
Applicative Maybe	Since: base-2.1
Instance details Defined in GHC.Base Methods pure :: a -> Maybe a # (<>) :: Maybe (a -> b) -> Maybe a -> Maybe b # liftA2 :: (a -> b -> c) -> Maybe a -> Maybe b -> Maybe c # (>) :: Maybe a -> Maybe b -> Maybe b # (<*) :: Maybe a -> Maybe b -> Maybe a #
Applicative IO	Since: base-2.1
Instance details Defined in GHC.Base Methods pure :: a -> IO a # (<>) :: IO (a -> b) -> IO a -> IO b # liftA2 :: (a -> b -> c) -> IO a -> IO b -> IO c # (>) :: IO a -> IO b -> IO b # (<*) :: IO a -> IO b -> IO a #
Applicative Par1	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods pure :: a -> Par1 a # (<>) :: Par1 (a -> b) -> Par1 a -> Par1 b # liftA2 :: (a -> b -> c) -> Par1 a -> Par1 b -> Par1 c # (>) :: Par1 a -> Par1 b -> Par1 b # (<*) :: Par1 a -> Par1 b -> Par1 a #
Applicative Complex	Since: base-4.9.0.0
Instance details Defined in Data.Complex Methods pure :: a -> Complex a # (<>) :: Complex (a -> b) -> Complex a -> Complex b # liftA2 :: (a -> b -> c) -> Complex a -> Complex b -> Complex c # (>) :: Complex a -> Complex b -> Complex b # (<*) :: Complex a -> Complex b -> Complex a #
Applicative Min	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods pure :: a -> Min a # (<>) :: Min (a -> b) -> Min a -> Min b # liftA2 :: (a -> b -> c) -> Min a -> Min b -> Min c # (>) :: Min a -> Min b -> Min b # (<*) :: Min a -> Min b -> Min a #
Applicative Max	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods pure :: a -> Max a # (<>) :: Max (a -> b) -> Max a -> Max b # liftA2 :: (a -> b -> c) -> Max a -> Max b -> Max c # (>) :: Max a -> Max b -> Max b # (<*) :: Max a -> Max b -> Max a #
Applicative First	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods pure :: a -> First a # (<>) :: First (a -> b) -> First a -> First b # liftA2 :: (a -> b -> c) -> First a -> First b -> First c # (>) :: First a -> First b -> First b # (<*) :: First a -> First b -> First a #
Applicative Last	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods pure :: a -> Last a # (<>) :: Last (a -> b) -> Last a -> Last b # liftA2 :: (a -> b -> c) -> Last a -> Last b -> Last c # (>) :: Last a -> Last b -> Last b # (<*) :: Last a -> Last b -> Last a #
Applicative Option	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods pure :: a -> Option a # (<>) :: Option (a -> b) -> Option a -> Option b # liftA2 :: (a -> b -> c) -> Option a -> Option b -> Option c # (>) :: Option a -> Option b -> Option b # (<*) :: Option a -> Option b -> Option a #
Applicative ZipList	f '<$>' 'ZipList' xs1 '<>' ... '<>' 'ZipList' xsN = 'ZipList' (zipWithN f xs1 ... xsN) where `zipWithN` refers to the `zipWith` function of the appropriate arity (`zipWith`, `zipWith3`, `zipWith4`, ...). For example: (\a b c -> stimes c [a, b]) <$> ZipList "abcd" <> ZipList "567" <> ZipList [1..] = ZipList (zipWith3 (\a b c -> stimes c [a, b]) "abcd" "567" [1..]) = ZipList {getZipList = ["a5","b6b6","c7c7c7"]} Since: base-2.1
Instance details Defined in Control.Applicative Methods pure :: a -> ZipList a # (<>) :: ZipList (a -> b) -> ZipList a -> ZipList b # liftA2 :: (a -> b -> c) -> ZipList a -> ZipList b -> ZipList c # (>) :: ZipList a -> ZipList b -> ZipList b # (<*) :: ZipList a -> ZipList b -> ZipList a #
Applicative Identity	Since: base-4.8.0.0
Instance details Defined in Data.Functor.Identity Methods pure :: a -> Identity a # (<>) :: Identity (a -> b) -> Identity a -> Identity b # liftA2 :: (a -> b -> c) -> Identity a -> Identity b -> Identity c # (>) :: Identity a -> Identity b -> Identity b # (<*) :: Identity a -> Identity b -> Identity a #
Applicative STM	Since: base-4.8.0.0
Instance details Defined in GHC.Conc.Sync Methods pure :: a -> STM a # (<>) :: STM (a -> b) -> STM a -> STM b # liftA2 :: (a -> b -> c) -> STM a -> STM b -> STM c # (>) :: STM a -> STM b -> STM b # (<*) :: STM a -> STM b -> STM a #
Applicative First	Since: base-4.8.0.0
Instance details Defined in Data.Monoid Methods pure :: a -> First a # (<>) :: First (a -> b) -> First a -> First b # liftA2 :: (a -> b -> c) -> First a -> First b -> First c # (>) :: First a -> First b -> First b # (<*) :: First a -> First b -> First a #
Applicative Last	Since: base-4.8.0.0
Instance details Defined in Data.Monoid Methods pure :: a -> Last a # (<>) :: Last (a -> b) -> Last a -> Last b # liftA2 :: (a -> b -> c) -> Last a -> Last b -> Last c # (>) :: Last a -> Last b -> Last b # (<*) :: Last a -> Last b -> Last a #
Applicative Dual	Since: base-4.8.0.0
Instance details Defined in Data.Semigroup.Internal Methods pure :: a -> Dual a # (<>) :: Dual (a -> b) -> Dual a -> Dual b # liftA2 :: (a -> b -> c) -> Dual a -> Dual b -> Dual c # (>) :: Dual a -> Dual b -> Dual b # (<*) :: Dual a -> Dual b -> Dual a #
Applicative Sum	Since: base-4.8.0.0
Instance details Defined in Data.Semigroup.Internal Methods pure :: a -> Sum a # (<>) :: Sum (a -> b) -> Sum a -> Sum b # liftA2 :: (a -> b -> c) -> Sum a -> Sum b -> Sum c # (>) :: Sum a -> Sum b -> Sum b # (<*) :: Sum a -> Sum b -> Sum a #
Applicative Product	Since: base-4.8.0.0
Instance details Defined in Data.Semigroup.Internal Methods pure :: a -> Product a # (<>) :: Product (a -> b) -> Product a -> Product b # liftA2 :: (a -> b -> c) -> Product a -> Product b -> Product c # (>) :: Product a -> Product b -> Product b # (<*) :: Product a -> Product b -> Product a #
Applicative Down	Since: base-4.11.0.0
Instance details Defined in Data.Ord Methods pure :: a -> Down a # (<>) :: Down (a -> b) -> Down a -> Down b # liftA2 :: (a -> b -> c) -> Down a -> Down b -> Down c # (>) :: Down a -> Down b -> Down b # (<*) :: Down a -> Down b -> Down a #
Applicative ReadPrec	Since: base-4.6.0.0
Instance details Defined in Text.ParserCombinators.ReadPrec Methods pure :: a -> ReadPrec a # (<>) :: ReadPrec (a -> b) -> ReadPrec a -> ReadPrec b # liftA2 :: (a -> b -> c) -> ReadPrec a -> ReadPrec b -> ReadPrec c # (>) :: ReadPrec a -> ReadPrec b -> ReadPrec b # (<*) :: ReadPrec a -> ReadPrec b -> ReadPrec a #
Applicative ReadP	Since: base-4.6.0.0
Instance details Defined in Text.ParserCombinators.ReadP Methods pure :: a -> ReadP a # (<>) :: ReadP (a -> b) -> ReadP a -> ReadP b # liftA2 :: (a -> b -> c) -> ReadP a -> ReadP b -> ReadP c # (>) :: ReadP a -> ReadP b -> ReadP b # (<*) :: ReadP a -> ReadP b -> ReadP a #
Applicative NonEmpty	Since: base-4.9.0.0
Instance details Defined in GHC.Base Methods pure :: a -> NonEmpty a # (<>) :: NonEmpty (a -> b) -> NonEmpty a -> NonEmpty b # liftA2 :: (a -> b -> c) -> NonEmpty a -> NonEmpty b -> NonEmpty c # (>) :: NonEmpty a -> NonEmpty b -> NonEmpty b # (<*) :: NonEmpty a -> NonEmpty b -> NonEmpty a #
Applicative PutM
Instance details Defined in Data.Binary.Put Methods pure :: a -> PutM a # (<>) :: PutM (a -> b) -> PutM a -> PutM b # liftA2 :: (a -> b -> c) -> PutM a -> PutM b -> PutM c # (>) :: PutM a -> PutM b -> PutM b # (<*) :: PutM a -> PutM b -> PutM a #
Applicative Get
Instance details Defined in Data.Binary.Get.Internal Methods pure :: a -> Get a # (<>) :: Get (a -> b) -> Get a -> Get b # liftA2 :: (a -> b -> c) -> Get a -> Get b -> Get c # (>) :: Get a -> Get b -> Get b # (<*) :: Get a -> Get b -> Get a #
Applicative Put
Instance details Defined in Data.ByteString.Builder.Internal Methods pure :: a -> Put a # (<>) :: Put (a -> b) -> Put a -> Put b # liftA2 :: (a -> b -> c) -> Put a -> Put b -> Put c # (>) :: Put a -> Put b -> Put b # (<*) :: Put a -> Put b -> Put a #
Applicative Tree
Instance details Defined in Data.Tree Methods pure :: a -> Tree a # (<>) :: Tree (a -> b) -> Tree a -> Tree b # liftA2 :: (a -> b -> c) -> Tree a -> Tree b -> Tree c # (>) :: Tree a -> Tree b -> Tree b # (<*) :: Tree a -> Tree b -> Tree a #
Applicative Seq	Since: containers-0.5.4
Instance details Defined in Data.Sequence.Internal Methods pure :: a -> Seq a # (<>) :: Seq (a -> b) -> Seq a -> Seq b # liftA2 :: (a -> b -> c) -> Seq a -> Seq b -> Seq c # (>) :: Seq a -> Seq b -> Seq b # (<*) :: Seq a -> Seq b -> Seq a #
Applicative P	Since: base-4.5.0.0
Instance details Defined in Text.ParserCombinators.ReadP Methods pure :: a -> P a # (<>) :: P (a -> b) -> P a -> P b # liftA2 :: (a -> b -> c) -> P a -> P b -> P c # (>) :: P a -> P b -> P b # (<*) :: P a -> P b -> P a #
Applicative Q Source #
Instance details Defined in Language.Haskell.TH.Syntax Methods pure :: a -> Q a # (<>) :: Q (a -> b) -> Q a -> Q b # liftA2 :: (a -> b -> c) -> Q a -> Q b -> Q c # (>) :: Q a -> Q b -> Q b # (<*) :: Q a -> Q b -> Q a #
Applicative PprM Source #
Instance details Defined in Language.Haskell.TH.PprLib Methods pure :: a -> PprM a # (<>) :: PprM (a -> b) -> PprM a -> PprM b # liftA2 :: (a -> b -> c) -> PprM a -> PprM b -> PprM c # (>) :: PprM a -> PprM b -> PprM b # (<*) :: PprM a -> PprM b -> PprM a #
Applicative Pair Source #
Instance details Defined in Pair Methods pure :: a -> Pair a # (<>) :: Pair (a -> b) -> Pair a -> Pair b # liftA2 :: (a -> b -> c) -> Pair a -> Pair b -> Pair c # (>) :: Pair a -> Pair b -> Pair b # (<*) :: Pair a -> Pair b -> Pair a #
Applicative UniqSM Source #
Instance details Defined in UniqSupply Methods pure :: a -> UniqSM a # (<>) :: UniqSM (a -> b) -> UniqSM a -> UniqSM b # liftA2 :: (a -> b -> c) -> UniqSM a -> UniqSM b -> UniqSM c # (>) :: UniqSM a -> UniqSM b -> UniqSM b # (<*) :: UniqSM a -> UniqSM b -> UniqSM a #
Applicative CoreM Source #
Instance details Defined in CoreMonad Methods pure :: a -> CoreM a # (<>) :: CoreM (a -> b) -> CoreM a -> CoreM b # liftA2 :: (a -> b -> c) -> CoreM a -> CoreM b -> CoreM c # (>) :: CoreM a -> CoreM b -> CoreM b # (<*) :: CoreM a -> CoreM b -> CoreM a #
Applicative P Source #
Instance details Defined in Lexer Methods pure :: a -> P a # (<>) :: P (a -> b) -> P a -> P b # liftA2 :: (a -> b -> c) -> P a -> P b -> P c # (>) :: P a -> P b -> P b # (<*) :: P a -> P b -> P a #
Applicative UnifyResultM Source #
Instance details Defined in Unify Methods pure :: a -> UnifyResultM a # (<>) :: UnifyResultM (a -> b) -> UnifyResultM a -> UnifyResultM b # liftA2 :: (a -> b -> c) -> UnifyResultM a -> UnifyResultM b -> UnifyResultM c # (>) :: UnifyResultM a -> UnifyResultM b -> UnifyResultM b # (<*) :: UnifyResultM a -> UnifyResultM b -> UnifyResultM a #
Applicative PV Source #
Instance details Defined in RdrHsSyn Methods pure :: a -> PV a # (<>) :: PV (a -> b) -> PV a -> PV b # liftA2 :: (a -> b -> c) -> PV a -> PV b -> PV c # (>) :: PV a -> PV b -> PV b # (<*) :: PV a -> PV b -> PV a #
Applicative Hsc Source #
Instance details Defined in HscTypes Methods pure :: a -> Hsc a # (<>) :: Hsc (a -> b) -> Hsc a -> Hsc b # liftA2 :: (a -> b -> c) -> Hsc a -> Hsc b -> Hsc c # (>) :: Hsc a -> Hsc b -> Hsc b # (<*) :: Hsc a -> Hsc b -> Hsc a #
Applicative CompPipeline Source #
Instance details Defined in PipelineMonad Methods pure :: a -> CompPipeline a # (<>) :: CompPipeline (a -> b) -> CompPipeline a -> CompPipeline b # liftA2 :: (a -> b -> c) -> CompPipeline a -> CompPipeline b -> CompPipeline c # (>) :: CompPipeline a -> CompPipeline b -> CompPipeline b # (<*) :: CompPipeline a -> CompPipeline b -> CompPipeline a #
Applicative Ghc Source #
Instance details Defined in GhcMonad Methods pure :: a -> Ghc a # (<>) :: Ghc (a -> b) -> Ghc a -> Ghc b # liftA2 :: (a -> b -> c) -> Ghc a -> Ghc b -> Ghc c # (>) :: Ghc a -> Ghc b -> Ghc b # (<*) :: Ghc a -> Ghc b -> Ghc a #
Applicative TcPluginM Source #
Instance details Defined in TcRnTypes Methods pure :: a -> TcPluginM a # (<>) :: TcPluginM (a -> b) -> TcPluginM a -> TcPluginM b # liftA2 :: (a -> b -> c) -> TcPluginM a -> TcPluginM b -> TcPluginM c # (>) :: TcPluginM a -> TcPluginM b -> TcPluginM b # (<*) :: TcPluginM a -> TcPluginM b -> TcPluginM a #
Applicative (Either e)	Since: base-3.0
Instance details Defined in Data.Either Methods pure :: a -> Either e a # (<>) :: Either e (a -> b) -> Either e a -> Either e b # liftA2 :: (a -> b -> c) -> Either e a -> Either e b -> Either e c # (>) :: Either e a -> Either e b -> Either e b # (<*) :: Either e a -> Either e b -> Either e a #
Applicative (U1 :: Type -> Type)	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods pure :: a -> U1 a # (<>) :: U1 (a -> b) -> U1 a -> U1 b # liftA2 :: (a -> b -> c) -> U1 a -> U1 b -> U1 c # (>) :: U1 a -> U1 b -> U1 b # (<*) :: U1 a -> U1 b -> U1 a #
Monoid a => Applicative ((,) a)	For tuples, the `Monoid` constraint on `a` determines how the first values merge. For example, `String`s concatenate: ("hello ", (+15)) <> ("world!", 2002) ("hello world!",2017) Since: base-2.1*
Instance details Defined in GHC.Base Methods pure :: a0 -> (a, a0) # (<>) :: (a, a0 -> b) -> (a, a0) -> (a, b) # liftA2 :: (a0 -> b -> c) -> (a, a0) -> (a, b) -> (a, c) # (>) :: (a, a0) -> (a, b) -> (a, b) # (<*) :: (a, a0) -> (a, b) -> (a, a0) #
Monad m => Applicative (WrappedMonad m)	Since: base-2.1
Instance details Defined in Control.Applicative Methods pure :: a -> WrappedMonad m a # (<>) :: WrappedMonad m (a -> b) -> WrappedMonad m a -> WrappedMonad m b # liftA2 :: (a -> b -> c) -> WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m c # (>) :: WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m b # (<*) :: WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m a #
Arrow a => Applicative (ArrowMonad a)	Since: base-4.6.0.0
Instance details Defined in Control.Arrow Methods pure :: a0 -> ArrowMonad a a0 # (<>) :: ArrowMonad a (a0 -> b) -> ArrowMonad a a0 -> ArrowMonad a b # liftA2 :: (a0 -> b -> c) -> ArrowMonad a a0 -> ArrowMonad a b -> ArrowMonad a c # (>) :: ArrowMonad a a0 -> ArrowMonad a b -> ArrowMonad a b # (<*) :: ArrowMonad a a0 -> ArrowMonad a b -> ArrowMonad a a0 #
Applicative (Proxy :: Type -> Type)	Since: base-4.7.0.0
Instance details Defined in Data.Proxy Methods pure :: a -> Proxy a # (<>) :: Proxy (a -> b) -> Proxy a -> Proxy b # liftA2 :: (a -> b -> c) -> Proxy a -> Proxy b -> Proxy c # (>) :: Proxy a -> Proxy b -> Proxy b # (<*) :: Proxy a -> Proxy b -> Proxy a #
(Functor m, Monad m) => Applicative (MaybeT m)
Instance details Defined in Control.Monad.Trans.Maybe Methods pure :: a -> MaybeT m a # (<>) :: MaybeT m (a -> b) -> MaybeT m a -> MaybeT m b # liftA2 :: (a -> b -> c) -> MaybeT m a -> MaybeT m b -> MaybeT m c # (>) :: MaybeT m a -> MaybeT m b -> MaybeT m b # (<*) :: MaybeT m a -> MaybeT m b -> MaybeT m a #
Applicative (MaybeErr err) Source #
Instance details Defined in Maybes Methods pure :: a -> MaybeErr err a # (<>) :: MaybeErr err (a -> b) -> MaybeErr err a -> MaybeErr err b # liftA2 :: (a -> b -> c) -> MaybeErr err a -> MaybeErr err b -> MaybeErr err c # (>) :: MaybeErr err a -> MaybeErr err b -> MaybeErr err b # (<*) :: MaybeErr err a -> MaybeErr err b -> MaybeErr err a #
Applicative (SetM s)
Instance details Defined in Data.Graph Methods pure :: a -> SetM s a # (<>) :: SetM s (a -> b) -> SetM s a -> SetM s b # liftA2 :: (a -> b -> c) -> SetM s a -> SetM s b -> SetM s c # (>) :: SetM s a -> SetM s b -> SetM s b # (<*) :: SetM s a -> SetM s b -> SetM s a #
Applicative (CmdLineP s) Source #
Instance details Defined in CmdLineParser Methods pure :: a -> CmdLineP s a # (<>) :: CmdLineP s (a -> b) -> CmdLineP s a -> CmdLineP s b # liftA2 :: (a -> b -> c) -> CmdLineP s a -> CmdLineP s b -> CmdLineP s c # (>) :: CmdLineP s a -> CmdLineP s b -> CmdLineP s b # (<*) :: CmdLineP s a -> CmdLineP s b -> CmdLineP s a #
Monad m => Applicative (EwM m) Source #
Instance details Defined in CmdLineParser Methods pure :: a -> EwM m a # (<>) :: EwM m (a -> b) -> EwM m a -> EwM m b # liftA2 :: (a -> b -> c) -> EwM m a -> EwM m b -> EwM m c # (>) :: EwM m a -> EwM m b -> EwM m b # (<*) :: EwM m a -> EwM m b -> EwM m a #
Applicative (IOEnv m) Source #
Instance details Defined in IOEnv Methods pure :: a -> IOEnv m a # (<>) :: IOEnv m (a -> b) -> IOEnv m a -> IOEnv m b # liftA2 :: (a -> b -> c) -> IOEnv m a -> IOEnv m b -> IOEnv m c # (>) :: IOEnv m a -> IOEnv m b -> IOEnv m b # (<*) :: IOEnv m a -> IOEnv m b -> IOEnv m a #
Applicative m => Applicative (GhcT m) Source #
Instance details Defined in GhcMonad Methods pure :: a -> GhcT m a # (<>) :: GhcT m (a -> b) -> GhcT m a -> GhcT m b # liftA2 :: (a -> b -> c) -> GhcT m a -> GhcT m b -> GhcT m c # (>) :: GhcT m a -> GhcT m b -> GhcT m b # (<*) :: GhcT m a -> GhcT m b -> GhcT m a #
Applicative f => Applicative (Rec1 f)	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods pure :: a -> Rec1 f a # (<>) :: Rec1 f (a -> b) -> Rec1 f a -> Rec1 f b # liftA2 :: (a -> b -> c) -> Rec1 f a -> Rec1 f b -> Rec1 f c # (>) :: Rec1 f a -> Rec1 f b -> Rec1 f b # (<*) :: Rec1 f a -> Rec1 f b -> Rec1 f a #
Arrow a => Applicative (WrappedArrow a b)	Since: base-2.1
Instance details Defined in Control.Applicative Methods pure :: a0 -> WrappedArrow a b a0 # (<>) :: WrappedArrow a b (a0 -> b0) -> WrappedArrow a b a0 -> WrappedArrow a b b0 # liftA2 :: (a0 -> b0 -> c) -> WrappedArrow a b a0 -> WrappedArrow a b b0 -> WrappedArrow a b c # (>) :: WrappedArrow a b a0 -> WrappedArrow a b b0 -> WrappedArrow a b b0 # (<*) :: WrappedArrow a b a0 -> WrappedArrow a b b0 -> WrappedArrow a b a0 #
Monoid m => Applicative (Const m :: Type -> Type)	Since: base-2.0.1
Instance details Defined in Data.Functor.Const Methods pure :: a -> Const m a # (<>) :: Const m (a -> b) -> Const m a -> Const m b # liftA2 :: (a -> b -> c) -> Const m a -> Const m b -> Const m c # (>) :: Const m a -> Const m b -> Const m b # (<*) :: Const m a -> Const m b -> Const m a #
Applicative f => Applicative (Ap f)	Since: base-4.12.0.0
Instance details Defined in Data.Monoid Methods pure :: a -> Ap f a # (<>) :: Ap f (a -> b) -> Ap f a -> Ap f b # liftA2 :: (a -> b -> c) -> Ap f a -> Ap f b -> Ap f c # (>) :: Ap f a -> Ap f b -> Ap f b # (<*) :: Ap f a -> Ap f b -> Ap f a #
Applicative f => Applicative (Alt f)	Since: base-4.8.0.0
Instance details Defined in Data.Semigroup.Internal Methods pure :: a -> Alt f a # (<>) :: Alt f (a -> b) -> Alt f a -> Alt f b # liftA2 :: (a -> b -> c) -> Alt f a -> Alt f b -> Alt f c # (>) :: Alt f a -> Alt f b -> Alt f b # (<*) :: Alt f a -> Alt f b -> Alt f a #
(Applicative f, Monad f) => Applicative (WhenMissing f x)	Equivalent to `ReaderT k (ReaderT x (MaybeT f))`. Since: containers-0.5.9
Instance details Defined in Data.IntMap.Internal Methods pure :: a -> WhenMissing f x a # (<>) :: WhenMissing f x (a -> b) -> WhenMissing f x a -> WhenMissing f x b # liftA2 :: (a -> b -> c) -> WhenMissing f x a -> WhenMissing f x b -> WhenMissing f x c # (>) :: WhenMissing f x a -> WhenMissing f x b -> WhenMissing f x b # (<*) :: WhenMissing f x a -> WhenMissing f x b -> WhenMissing f x a #
(Monoid w, Applicative m) => Applicative (WriterT w m)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods pure :: a -> WriterT w m a # (<>) :: WriterT w m (a -> b) -> WriterT w m a -> WriterT w m b # liftA2 :: (a -> b -> c) -> WriterT w m a -> WriterT w m b -> WriterT w m c # (>) :: WriterT w m a -> WriterT w m b -> WriterT w m b # (<*) :: WriterT w m a -> WriterT w m b -> WriterT w m a #
(Functor m, Monad m) => Applicative (ExceptT e m)
Instance details Defined in Control.Monad.Trans.Except Methods pure :: a -> ExceptT e m a # (<>) :: ExceptT e m (a -> b) -> ExceptT e m a -> ExceptT e m b # liftA2 :: (a -> b -> c) -> ExceptT e m a -> ExceptT e m b -> ExceptT e m c # (>) :: ExceptT e m a -> ExceptT e m b -> ExceptT e m b # (<*) :: ExceptT e m a -> ExceptT e m b -> ExceptT e m a #
Applicative ((->) a :: Type -> Type)	Since: base-2.1
Instance details Defined in GHC.Base Methods pure :: a0 -> a -> a0 # (<>) :: (a -> (a0 -> b)) -> (a -> a0) -> a -> b # liftA2 :: (a0 -> b -> c) -> (a -> a0) -> (a -> b) -> a -> c # (>) :: (a -> a0) -> (a -> b) -> a -> b # (<*) :: (a -> a0) -> (a -> b) -> a -> a0 #
Monoid c => Applicative (K1 i c :: Type -> Type)	Since: base-4.12.0.0
Instance details Defined in GHC.Generics Methods pure :: a -> K1 i c a # (<>) :: K1 i c (a -> b) -> K1 i c a -> K1 i c b # liftA2 :: (a -> b -> c0) -> K1 i c a -> K1 i c b -> K1 i c c0 # (>) :: K1 i c a -> K1 i c b -> K1 i c b # (<*) :: K1 i c a -> K1 i c b -> K1 i c a #
(Applicative f, Applicative g) => Applicative (f :*: g)	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods pure :: a -> (f :: g) a # (<>) :: (f :: g) (a -> b) -> (f :: g) a -> (f :: g) b # liftA2 :: (a -> b -> c) -> (f :: g) a -> (f :: g) b -> (f :: g) c # (>) :: (f :: g) a -> (f :: g) b -> (f :: g) b # (<) :: (f :: g) a -> (f :: g) b -> (f :: g) a #
(Applicative f, Applicative g) => Applicative (Product f g)	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Product Methods pure :: a -> Product f g a # (<>) :: Product f g (a -> b) -> Product f g a -> Product f g b # liftA2 :: (a -> b -> c) -> Product f g a -> Product f g b -> Product f g c # (>) :: Product f g a -> Product f g b -> Product f g b # (<*) :: Product f g a -> Product f g b -> Product f g a #
(Monad f, Applicative f) => Applicative (WhenMatched f x y)	Equivalent to `ReaderT Key (ReaderT x (ReaderT y (MaybeT f)))` Since: containers-0.5.9
Instance details Defined in Data.IntMap.Internal Methods pure :: a -> WhenMatched f x y a # (<>) :: WhenMatched f x y (a -> b) -> WhenMatched f x y a -> WhenMatched f x y b # liftA2 :: (a -> b -> c) -> WhenMatched f x y a -> WhenMatched f x y b -> WhenMatched f x y c # (>) :: WhenMatched f x y a -> WhenMatched f x y b -> WhenMatched f x y b # (<*) :: WhenMatched f x y a -> WhenMatched f x y b -> WhenMatched f x y a #
(Applicative f, Monad f) => Applicative (WhenMissing f k x)	Equivalent to `ReaderT k (ReaderT x (MaybeT f))` . Since: containers-0.5.9
Instance details Defined in Data.Map.Internal Methods pure :: a -> WhenMissing f k x a # (<>) :: WhenMissing f k x (a -> b) -> WhenMissing f k x a -> WhenMissing f k x b # liftA2 :: (a -> b -> c) -> WhenMissing f k x a -> WhenMissing f k x b -> WhenMissing f k x c # (>) :: WhenMissing f k x a -> WhenMissing f k x b -> WhenMissing f k x b # (<*) :: WhenMissing f k x a -> WhenMissing f k x b -> WhenMissing f k x a #
Applicative m => Applicative (ReaderT r m)
Instance details Defined in Control.Monad.Trans.Reader Methods pure :: a -> ReaderT r m a # (<>) :: ReaderT r m (a -> b) -> ReaderT r m a -> ReaderT r m b # liftA2 :: (a -> b -> c) -> ReaderT r m a -> ReaderT r m b -> ReaderT r m c # (>) :: ReaderT r m a -> ReaderT r m b -> ReaderT r m b # (<*) :: ReaderT r m a -> ReaderT r m b -> ReaderT r m a #
Applicative f => Applicative (M1 i c f)	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods pure :: a -> M1 i c f a # (<>) :: M1 i c f (a -> b) -> M1 i c f a -> M1 i c f b # liftA2 :: (a -> b -> c0) -> M1 i c f a -> M1 i c f b -> M1 i c f c0 # (>) :: M1 i c f a -> M1 i c f b -> M1 i c f b # (<*) :: M1 i c f a -> M1 i c f b -> M1 i c f a #
(Applicative f, Applicative g) => Applicative (f :.: g)	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods pure :: a -> (f :.: g) a # (<>) :: (f :.: g) (a -> b) -> (f :.: g) a -> (f :.: g) b # liftA2 :: (a -> b -> c) -> (f :.: g) a -> (f :.: g) b -> (f :.: g) c # (>) :: (f :.: g) a -> (f :.: g) b -> (f :.: g) b # (<*) :: (f :.: g) a -> (f :.: g) b -> (f :.: g) a #
(Applicative f, Applicative g) => Applicative (Compose f g)	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Compose Methods pure :: a -> Compose f g a # (<>) :: Compose f g (a -> b) -> Compose f g a -> Compose f g b # liftA2 :: (a -> b -> c) -> Compose f g a -> Compose f g b -> Compose f g c # (>) :: Compose f g a -> Compose f g b -> Compose f g b # (<*) :: Compose f g a -> Compose f g b -> Compose f g a #
(Monad f, Applicative f) => Applicative (WhenMatched f k x y)	Equivalent to `ReaderT k (ReaderT x (ReaderT y (MaybeT f)))` Since: containers-0.5.9
Instance details Defined in Data.Map.Internal Methods pure :: a -> WhenMatched f k x y a # (<>) :: WhenMatched f k x y (a -> b) -> WhenMatched f k x y a -> WhenMatched f k x y b # liftA2 :: (a -> b -> c) -> WhenMatched f k x y a -> WhenMatched f k x y b -> WhenMatched f k x y c # (>) :: WhenMatched f k x y a -> WhenMatched f k x y b -> WhenMatched f k x y b # (<*) :: WhenMatched f k x y a -> WhenMatched f k x y b -> WhenMatched f k x y a #

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

An infix synonym for fmap.

The name of this operator is an allusion to $. Note the similarities between their types:

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

Whereas $ is function application, <$> is function application lifted over a Functor.

Examples

Expand

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 :: Type -> Type) where #

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 #

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 []	Since: base-2.1
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> [a]) -> [a] #
MonadFix Maybe	Since: base-2.1
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> Maybe a) -> Maybe a #
MonadFix IO	Since: base-2.1
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> IO a) -> IO a #
MonadFix Par1	Since: base-4.9.0.0
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> Par1 a) -> Par1 a #
MonadFix Min	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods mfix :: (a -> Min a) -> Min a #
MonadFix Max	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods mfix :: (a -> Max a) -> Max a #
MonadFix First	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods mfix :: (a -> First a) -> First a #
MonadFix Last	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods mfix :: (a -> Last a) -> Last a #
MonadFix Option	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods mfix :: (a -> Option a) -> Option a #
MonadFix Identity	Since: base-4.8.0.0
Instance details Defined in Data.Functor.Identity Methods mfix :: (a -> Identity a) -> Identity a #
MonadFix First	Since: base-4.8.0.0
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> First a) -> First a #
MonadFix Last	Since: base-4.8.0.0
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> Last a) -> Last a #
MonadFix Dual	Since: base-4.8.0.0
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> Dual a) -> Dual a #
MonadFix Sum	Since: base-4.8.0.0
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> Sum a) -> Sum a #
MonadFix Product	Since: base-4.8.0.0
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> Product a) -> Product a #
MonadFix Down	Since: base-4.12.0.0
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> Down a) -> Down a #
MonadFix NonEmpty	Since: base-4.9.0.0
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> NonEmpty a) -> NonEmpty a #
MonadFix Tree	Since: containers-0.5.11
Instance details Defined in Data.Tree Methods mfix :: (a -> Tree a) -> Tree a #
MonadFix Seq	Since: containers-0.5.11
Instance details Defined in Data.Sequence.Internal Methods mfix :: (a -> Seq a) -> Seq a #
MonadFix UniqSM Source #
Instance details Defined in UniqSupply Methods mfix :: (a -> UniqSM a) -> UniqSM a #
MonadFix Ghc Source #
Instance details Defined in GhcMonad Methods mfix :: (a -> Ghc a) -> Ghc a #
MonadFix (Either e)	Since: base-4.3.0.0
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> Either e a) -> Either e a #
MonadFix (ST s)	Since: base-2.1
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> ST s a) -> ST s a #
MonadFix m => MonadFix (MaybeT m)
Instance details Defined in Control.Monad.Trans.Maybe Methods mfix :: (a -> MaybeT m a) -> MaybeT m a #
MonadFix f => MonadFix (Rec1 f)	Since: base-4.9.0.0
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> Rec1 f a) -> Rec1 f a #
MonadFix f => MonadFix (Ap f)	Since: base-4.12.0.0
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> Ap f a) -> Ap f a #
MonadFix f => MonadFix (Alt f)	Since: base-4.8.0.0
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> Alt f a) -> Alt f a #
(Monoid w, MonadFix m) => MonadFix (WriterT w m)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods mfix :: (a -> WriterT w m a) -> WriterT w m a #
MonadFix m => MonadFix (ExceptT e m)
Instance details Defined in Control.Monad.Trans.Except Methods mfix :: (a -> ExceptT e m a) -> ExceptT e m a #
MonadFix ((->) r :: Type -> Type)	Since: base-2.1
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> r -> a) -> r -> a #
(MonadFix f, MonadFix g) => MonadFix (f :*: g)	Since: base-4.9.0.0
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> (f :: g) a) -> (f :: g) a #
(MonadFix f, MonadFix g) => MonadFix (Product f g)	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Product Methods mfix :: (a -> Product f g a) -> Product f g a #
MonadFix m => MonadFix (ReaderT r m)
Instance details Defined in Control.Monad.Trans.Reader Methods mfix :: (a -> ReaderT r m a) -> ReaderT r m a #
MonadFix f => MonadFix (M1 i c f)	Since: base-4.9.0.0
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> M1 i c f a) -> M1 i c f a #

class Monad m => MonadIO (m :: Type -> Type) where #

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 #

Lift a computation from the IO monad.

Instances

MonadIO IO	Since: base-4.9.0.0
Instance details Defined in Control.Monad.IO.Class Methods liftIO :: IO a -> IO a #
MonadIO Q Source #
Instance details Defined in Language.Haskell.TH.Syntax Methods liftIO :: IO a -> Q a #
MonadIO CoreM Source #
Instance details Defined in CoreMonad Methods liftIO :: IO a -> CoreM a #
MonadIO Hsc Source #
Instance details Defined in HscTypes Methods liftIO :: IO a -> Hsc a #
MonadIO CompPipeline Source #
Instance details Defined in PipelineMonad Methods liftIO :: IO a -> CompPipeline a #
MonadIO Ghc Source #
Instance details Defined in GhcMonad Methods liftIO :: IO a -> Ghc a #
MonadIO m => MonadIO (MaybeT m)
Instance details Defined in Control.Monad.Trans.Maybe Methods liftIO :: IO a -> MaybeT m a #
MonadIO (IOEnv env) Source #
Instance details Defined in IOEnv Methods liftIO :: IO a -> IOEnv env a #
MonadIO m => MonadIO (GhcT m) Source #
Instance details Defined in GhcMonad Methods liftIO :: IO a -> GhcT m a #
(Monoid w, MonadIO m) => MonadIO (WriterT w m)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods liftIO :: IO a -> WriterT w m a #
MonadIO m => MonadIO (ExceptT e m)
Instance details Defined in Control.Monad.Trans.Except Methods liftIO :: IO a -> ExceptT e m a #
MonadIO m => MonadIO (ReaderT r m)
Instance details Defined in Control.Monad.Trans.Reader Methods liftIO :: IO a -> ReaderT r m a #

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 #

zipWith4M :: Monad m => (a -> b -> c -> d -> m e) -> [a] -> [b] -> [c] -> [d] -> m [e] Source #

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

mapAndUnzipM :: Applicative m => (a -> m (b, c)) -> [a] -> m ([b], [c]) #

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 #

mapAndUnzip5M :: Monad m => (a -> m (b, c, d, e, f)) -> [a] -> m ([b], [c], [d], [e], [f]) Source #

mapAccumLM Source #

Arguments

:: Monad m
=> (acc -> x -> m (acc, y))	combining function
-> 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 :: Applicative m => (a -> m (Maybe b)) -> [a] -> m [b] Source #

Applicative 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

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

Monadic version of or

foldlM :: (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m b #

Monadic fold over the elements of a structure, associating to the left, i.e. from left to right.

foldlM_ :: (Monad m, Foldable t) => (a -> b -> m a) -> a -> t b -> m () Source #

Monadic version of foldl that discards its result

foldrM :: (Foldable t, Monad m) => (a -> b -> m b) -> b -> t a -> m b #

Monadic fold over the elements of a structure, associating to the right, i.e. from right to left.

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

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

Monadic version of unless, taking the condition in the monad

filterOutM :: Applicative m => (a -> m Bool) -> [a] -> m [a] Source #

Like filterM, only it reverses the sense of the test.