Safe Haskell	Safe-Inferred
Language	Haskell2010

GHC.Utils.Monad

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 Source #

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
```

m1 <*> m2 = m1 >>= (x1 -> m2 >>= (x2 -> return (x1 x2)))

```
(*>) = (>>)
```

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

Minimal complete definition

pure, ((<*>) | liftA2)

Methods

pure :: a -> f a Source #

Lift a value.

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

Sequential application.

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

Example

Expand

Used in combination with (<$>), (<*>) can be used to build a record.

>>> data MyState = MyState {arg1 :: Foo, arg2 :: Bar, arg3 :: Baz}

>>> produceFoo :: Applicative f => f Foo

>>> produceBar :: Applicative f => f Bar
>>> produceBaz :: Applicative f => f Baz

>>> mkState :: Applicative f => f MyState
>>> mkState = MyState <$> produceFoo <*> produceBar <*> produceBaz

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

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 <*>.

This became a typeclass method in 4.10.0.0. Prior to that, it was a function defined in terms of <*> and fmap.

Example

Expand

>>> liftA2 (,) (Just 3) (Just 5)
Just (3,5)

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

Sequence actions, discarding the value of the first argument.

Examples

Expand

If used in conjunction with the Applicative instance for Maybe, you can chain Maybe computations, with a possible "early return" in case of Nothing.

>>> Just 2 *> Just 3
Just 3

>>> Nothing *> Just 3
Nothing

Of course a more interesting use case would be to have effectful computations instead of just returning pure values.

>>> import Data.Char
>>> import Text.ParserCombinators.ReadP
>>> let p = string "my name is " *> munch1 isAlpha <* eof
>>> readP_to_S p "my name is Simon"
[("Simon","")]

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

Sequence actions, discarding the value of the second argument.

Instances

Instances details

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 Source # (<>) :: ZipList (a -> b) -> ZipList a -> ZipList b Source # liftA2 :: (a -> b -> c) -> ZipList a -> ZipList b -> ZipList c Source # (>) :: ZipList a -> ZipList b -> ZipList b Source # (<*) :: ZipList a -> ZipList b -> ZipList a Source #
Applicative Complex	Since: base-4.9.0.0
Instance details Defined in Data.Complex Methods pure :: a -> Complex a Source # (<>) :: Complex (a -> b) -> Complex a -> Complex b Source # liftA2 :: (a -> b -> c) -> Complex a -> Complex b -> Complex c Source # (>) :: Complex a -> Complex b -> Complex b Source # (<*) :: Complex a -> Complex b -> Complex a Source #
Applicative Identity	Since: base-4.8.0.0
Instance details Defined in Data.Functor.Identity Methods pure :: a -> Identity a Source # (<>) :: Identity (a -> b) -> Identity a -> Identity b Source # liftA2 :: (a -> b -> c) -> Identity a -> Identity b -> Identity c Source # (>) :: Identity a -> Identity b -> Identity b Source # (<*) :: Identity a -> Identity b -> Identity a Source #
Applicative First	Since: base-4.8.0.0
Instance details Defined in Data.Monoid Methods pure :: a -> First a Source # (<>) :: First (a -> b) -> First a -> First b Source # liftA2 :: (a -> b -> c) -> First a -> First b -> First c Source # (>) :: First a -> First b -> First b Source # (<*) :: First a -> First b -> First a Source #
Applicative Last	Since: base-4.8.0.0
Instance details Defined in Data.Monoid Methods pure :: a -> Last a Source # (<>) :: Last (a -> b) -> Last a -> Last b Source # liftA2 :: (a -> b -> c) -> Last a -> Last b -> Last c Source # (>) :: Last a -> Last b -> Last b Source # (<*) :: Last a -> Last b -> Last a Source #
Applicative Down	Since: base-4.11.0.0
Instance details Defined in Data.Ord Methods pure :: a -> Down a Source # (<>) :: Down (a -> b) -> Down a -> Down b Source # liftA2 :: (a -> b -> c) -> Down a -> Down b -> Down c Source # (>) :: Down a -> Down b -> Down b Source # (<*) :: Down a -> Down b -> Down a Source #
Applicative First	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods pure :: a -> First a Source # (<>) :: First (a -> b) -> First a -> First b Source # liftA2 :: (a -> b -> c) -> First a -> First b -> First c Source # (>) :: First a -> First b -> First b Source # (<*) :: First a -> First b -> First a Source #
Applicative Last	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods pure :: a -> Last a Source # (<>) :: Last (a -> b) -> Last a -> Last b Source # liftA2 :: (a -> b -> c) -> Last a -> Last b -> Last c Source # (>) :: Last a -> Last b -> Last b Source # (<*) :: Last a -> Last b -> Last a Source #
Applicative Max	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods pure :: a -> Max a Source # (<>) :: Max (a -> b) -> Max a -> Max b Source # liftA2 :: (a -> b -> c) -> Max a -> Max b -> Max c Source # (>) :: Max a -> Max b -> Max b Source # (<*) :: Max a -> Max b -> Max a Source #
Applicative Min	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods pure :: a -> Min a Source # (<>) :: Min (a -> b) -> Min a -> Min b Source # liftA2 :: (a -> b -> c) -> Min a -> Min b -> Min c Source # (>) :: Min a -> Min b -> Min b Source # (<*) :: Min a -> Min b -> Min a Source #
Applicative Option	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods pure :: a -> Option a Source # (<>) :: Option (a -> b) -> Option a -> Option b Source # liftA2 :: (a -> b -> c) -> Option a -> Option b -> Option c Source # (>) :: Option a -> Option b -> Option b Source # (<*) :: Option a -> Option b -> Option a Source #
Applicative Dual	Since: base-4.8.0.0
Instance details Defined in Data.Semigroup.Internal Methods pure :: a -> Dual a Source # (<>) :: Dual (a -> b) -> Dual a -> Dual b Source # liftA2 :: (a -> b -> c) -> Dual a -> Dual b -> Dual c Source # (>) :: Dual a -> Dual b -> Dual b Source # (<*) :: Dual a -> Dual b -> Dual a Source #
Applicative Product	Since: base-4.8.0.0
Instance details Defined in Data.Semigroup.Internal Methods pure :: a -> Product a Source # (<>) :: Product (a -> b) -> Product a -> Product b Source # liftA2 :: (a -> b -> c) -> Product a -> Product b -> Product c Source # (>) :: Product a -> Product b -> Product b Source # (<*) :: Product a -> Product b -> Product a Source #
Applicative Sum	Since: base-4.8.0.0
Instance details Defined in Data.Semigroup.Internal Methods pure :: a -> Sum a Source # (<>) :: Sum (a -> b) -> Sum a -> Sum b Source # liftA2 :: (a -> b -> c) -> Sum a -> Sum b -> Sum c Source # (>) :: Sum a -> Sum b -> Sum b Source # (<*) :: Sum a -> Sum b -> Sum a Source #
Applicative NonEmpty	Since: base-4.9.0.0
Instance details Defined in GHC.Base Methods pure :: a -> NonEmpty a Source # (<>) :: NonEmpty (a -> b) -> NonEmpty a -> NonEmpty b Source # liftA2 :: (a -> b -> c) -> NonEmpty a -> NonEmpty b -> NonEmpty c Source # (>) :: NonEmpty a -> NonEmpty b -> NonEmpty b Source # (<*) :: NonEmpty a -> NonEmpty b -> NonEmpty a Source #
Applicative STM	Since: base-4.8.0.0
Instance details Defined in GHC.Conc.Sync Methods pure :: a -> STM a Source # (<>) :: STM (a -> b) -> STM a -> STM b Source # liftA2 :: (a -> b -> c) -> STM a -> STM b -> STM c Source # (>) :: STM a -> STM b -> STM b Source # (<*) :: STM a -> STM b -> STM a Source #
Applicative Par1	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods pure :: a -> Par1 a Source # (<>) :: Par1 (a -> b) -> Par1 a -> Par1 b Source # liftA2 :: (a -> b -> c) -> Par1 a -> Par1 b -> Par1 c Source # (>) :: Par1 a -> Par1 b -> Par1 b Source # (<*) :: Par1 a -> Par1 b -> Par1 a Source #
Applicative P	Since: base-4.5.0.0
Instance details Defined in Text.ParserCombinators.ReadP Methods pure :: a -> P a Source # (<>) :: P (a -> b) -> P a -> P b Source # liftA2 :: (a -> b -> c) -> P a -> P b -> P c Source # (>) :: P a -> P b -> P b Source # (<*) :: P a -> P b -> P a Source #
Applicative ReadP	Since: base-4.6.0.0
Instance details Defined in Text.ParserCombinators.ReadP Methods pure :: a -> ReadP a Source # (<>) :: ReadP (a -> b) -> ReadP a -> ReadP b Source # liftA2 :: (a -> b -> c) -> ReadP a -> ReadP b -> ReadP c Source # (>) :: ReadP a -> ReadP b -> ReadP b Source # (<*) :: ReadP a -> ReadP b -> ReadP a Source #
Applicative ReadPrec	Since: base-4.6.0.0
Instance details Defined in Text.ParserCombinators.ReadPrec Methods pure :: a -> ReadPrec a Source # (<>) :: ReadPrec (a -> b) -> ReadPrec a -> ReadPrec b Source # liftA2 :: (a -> b -> c) -> ReadPrec a -> ReadPrec b -> ReadPrec c Source # (>) :: ReadPrec a -> ReadPrec b -> ReadPrec b Source # (<*) :: ReadPrec a -> ReadPrec b -> ReadPrec a Source #
Applicative Get
Instance details Defined in Data.Binary.Get.Internal Methods pure :: a -> Get a Source # (<>) :: Get (a -> b) -> Get a -> Get b Source # liftA2 :: (a -> b -> c) -> Get a -> Get b -> Get c Source # (>) :: Get a -> Get b -> Get b Source # (<*) :: Get a -> Get b -> Get a Source #
Applicative PutM
Instance details Defined in Data.Binary.Put Methods pure :: a -> PutM a Source # (<>) :: PutM (a -> b) -> PutM a -> PutM b Source # liftA2 :: (a -> b -> c) -> PutM a -> PutM b -> PutM c Source # (>) :: PutM a -> PutM b -> PutM b Source # (<*) :: PutM a -> PutM b -> PutM a Source #
Applicative Put
Instance details Defined in Data.ByteString.Builder.Internal Methods pure :: a -> Put a Source # (<>) :: Put (a -> b) -> Put a -> Put b Source # liftA2 :: (a -> b -> c) -> Put a -> Put b -> Put c Source # (>) :: Put a -> Put b -> Put b Source # (<*) :: Put a -> Put b -> Put a Source #
Applicative Seq	Since: containers-0.5.4
Instance details Defined in Data.Sequence.Internal Methods pure :: a -> Seq a Source # (<>) :: Seq (a -> b) -> Seq a -> Seq b Source # liftA2 :: (a -> b -> c) -> Seq a -> Seq b -> Seq c Source # (>) :: Seq a -> Seq b -> Seq b Source # (<*) :: Seq a -> Seq b -> Seq a Source #
Applicative Tree
Instance details Defined in Data.Tree Methods pure :: a -> Tree a Source # (<>) :: Tree (a -> b) -> Tree a -> Tree b Source # liftA2 :: (a -> b -> c) -> Tree a -> Tree b -> Tree c Source # (>) :: Tree a -> Tree b -> Tree b Source # (<*) :: Tree a -> Tree b -> Tree a Source #
Applicative PD Source #
Instance details Defined in GHC.Cmm.Monad Methods pure :: a -> PD a Source # (<>) :: PD (a -> b) -> PD a -> PD b Source # liftA2 :: (a -> b -> c) -> PD a -> PD b -> PD c Source # (>) :: PD a -> PD b -> PD b Source # (<*) :: PD a -> PD b -> PD a Source #
Applicative NatM Source #
Instance details Defined in GHC.CmmToAsm.Monad Methods pure :: a -> NatM a Source # (<>) :: NatM (a -> b) -> NatM a -> NatM b Source # liftA2 :: (a -> b -> c) -> NatM a -> NatM b -> NatM c Source # (>) :: NatM a -> NatM b -> NatM b Source # (<*) :: NatM a -> NatM b -> NatM a Source #
Applicative LlvmM Source #
Instance details Defined in GHC.CmmToLlvm.Base Methods pure :: a -> LlvmM a Source # (<>) :: LlvmM (a -> b) -> LlvmM a -> LlvmM b Source # liftA2 :: (a -> b -> c) -> LlvmM a -> LlvmM b -> LlvmM c Source # (>) :: LlvmM a -> LlvmM b -> LlvmM b Source # (<*) :: LlvmM a -> LlvmM b -> LlvmM a Source #
Applicative CoreM Source #
Instance details Defined in GHC.Core.Opt.Monad Methods pure :: a -> CoreM a Source # (<>) :: CoreM (a -> b) -> CoreM a -> CoreM b Source # liftA2 :: (a -> b -> c) -> CoreM a -> CoreM b -> CoreM c Source # (>) :: CoreM a -> CoreM b -> CoreM b Source # (<*) :: CoreM a -> CoreM b -> CoreM a Source #
Applicative SimplM Source #
Instance details Defined in GHC.Core.Opt.Simplify.Monad Methods pure :: a -> SimplM a Source # (<>) :: SimplM (a -> b) -> SimplM a -> SimplM b Source # liftA2 :: (a -> b -> c) -> SimplM a -> SimplM b -> SimplM c Source # (>) :: SimplM a -> SimplM b -> SimplM b Source # (<*) :: SimplM a -> SimplM b -> SimplM a Source #
Applicative UnifyResultM Source #
Instance details Defined in GHC.Core.Unify Methods pure :: a -> UnifyResultM a Source # (<>) :: UnifyResultM (a -> b) -> UnifyResultM a -> UnifyResultM b Source # liftA2 :: (a -> b -> c) -> UnifyResultM a -> UnifyResultM b -> UnifyResultM c Source # (>) :: UnifyResultM a -> UnifyResultM b -> UnifyResultM b Source # (<*) :: UnifyResultM a -> UnifyResultM b -> UnifyResultM a Source #
Applicative Pair Source #
Instance details Defined in GHC.Data.Pair Methods pure :: a -> Pair a Source # (<>) :: Pair (a -> b) -> Pair a -> Pair b Source # liftA2 :: (a -> b -> c) -> Pair a -> Pair b -> Pair c Source # (>) :: Pair a -> Pair b -> Pair b Source # (<*) :: Pair a -> Pair b -> Pair a Source #
Applicative Ghc Source #
Instance details Defined in GHC.Driver.Monad Methods pure :: a -> Ghc a Source # (<>) :: Ghc (a -> b) -> Ghc a -> Ghc b Source # liftA2 :: (a -> b -> c) -> Ghc a -> Ghc b -> Ghc c Source # (>) :: Ghc a -> Ghc b -> Ghc b Source # (<*) :: Ghc a -> Ghc b -> Ghc a Source #
Applicative CompPipeline Source #
Instance details Defined in GHC.Driver.Pipeline.Monad Methods pure :: a -> CompPipeline a Source # (<>) :: CompPipeline (a -> b) -> CompPipeline a -> CompPipeline b Source # liftA2 :: (a -> b -> c) -> CompPipeline a -> CompPipeline b -> CompPipeline c Source # (>) :: CompPipeline a -> CompPipeline b -> CompPipeline b Source # (<*) :: CompPipeline a -> CompPipeline b -> CompPipeline a Source #
Applicative Hsc Source #
Instance details Defined in GHC.Driver.Types Methods pure :: a -> Hsc a Source # (<>) :: Hsc (a -> b) -> Hsc a -> Hsc b Source # liftA2 :: (a -> b -> c) -> Hsc a -> Hsc b -> Hsc c Source # (>) :: Hsc a -> Hsc b -> Hsc b Source # (<*) :: Hsc a -> Hsc b -> Hsc a Source #
Applicative MatchResult Source #	Product is an "or" on falliblity---the combined match result is infallible only if the left and right argument match results both were. This is useful for combining a bunch of alternatives together and then getting the overall falliblity of the entire group. See `mkDataConCase` for an example.
Instance details Defined in GHC.HsToCore.Monad Methods pure :: a -> MatchResult a Source # (<>) :: MatchResult (a -> b) -> MatchResult a -> MatchResult b Source # liftA2 :: (a -> b -> c) -> MatchResult a -> MatchResult b -> MatchResult c Source # (>) :: MatchResult a -> MatchResult b -> MatchResult b Source # (<*) :: MatchResult a -> MatchResult b -> MatchResult a Source #
Applicative P Source #
Instance details Defined in GHC.Parser.Lexer Methods pure :: a -> P a Source # (<>) :: P (a -> b) -> P a -> P b Source # liftA2 :: (a -> b -> c) -> P a -> P b -> P c Source # (>) :: P a -> P b -> P b Source # (<*) :: P a -> P b -> P a Source #
Applicative PV Source #
Instance details Defined in GHC.Parser.PostProcess Methods pure :: a -> PV a Source # (<>) :: PV (a -> b) -> PV a -> PV b Source # liftA2 :: (a -> b -> c) -> PV a -> PV b -> PV c Source # (>) :: PV a -> PV b -> PV b Source # (<*) :: PV a -> PV b -> PV a Source #
Applicative CpsRn Source #
Instance details Defined in GHC.Rename.Pat Methods pure :: a -> CpsRn a Source # (<>) :: CpsRn (a -> b) -> CpsRn a -> CpsRn b Source # liftA2 :: (a -> b -> c) -> CpsRn a -> CpsRn b -> CpsRn c Source # (>) :: CpsRn a -> CpsRn b -> CpsRn b Source # (<*) :: CpsRn a -> CpsRn b -> CpsRn a Source #
Applicative LiftM Source #
Instance details Defined in GHC.Stg.Lift.Monad Methods pure :: a -> LiftM a Source # (<>) :: LiftM (a -> b) -> LiftM a -> LiftM b Source # liftA2 :: (a -> b -> c) -> LiftM a -> LiftM b -> LiftM c Source # (>) :: LiftM a -> LiftM b -> LiftM b Source # (<*) :: LiftM a -> LiftM b -> LiftM a Source #
Applicative CmmParse Source #
Instance details Defined in GHC.StgToCmm.ExtCode Methods pure :: a -> CmmParse a Source # (<>) :: CmmParse (a -> b) -> CmmParse a -> CmmParse b Source # liftA2 :: (a -> b -> c) -> CmmParse a -> CmmParse b -> CmmParse c Source # (>) :: CmmParse a -> CmmParse b -> CmmParse b Source # (<*) :: CmmParse a -> CmmParse b -> CmmParse a Source #
Applicative FCode Source #
Instance details Defined in GHC.StgToCmm.Monad Methods pure :: a -> FCode a Source # (<>) :: FCode (a -> b) -> FCode a -> FCode b Source # liftA2 :: (a -> b -> c) -> FCode a -> FCode b -> FCode c Source # (>) :: FCode a -> FCode b -> FCode b Source # (<*) :: FCode a -> FCode b -> FCode a Source #
Applicative TcS Source #
Instance details Defined in GHC.Tc.Solver.Monad Methods pure :: a -> TcS a Source # (<>) :: TcS (a -> b) -> TcS a -> TcS b Source # liftA2 :: (a -> b -> c) -> TcS a -> TcS b -> TcS c Source # (>) :: TcS a -> TcS b -> TcS b Source # (<*) :: TcS a -> TcS b -> TcS a Source #
Applicative TcPluginM Source #
Instance details Defined in GHC.Tc.Types Methods pure :: a -> TcPluginM a Source # (<>) :: TcPluginM (a -> b) -> TcPluginM a -> TcPluginM b Source # liftA2 :: (a -> b -> c) -> TcPluginM a -> TcPluginM b -> TcPluginM c Source # (>) :: TcPluginM a -> TcPluginM b -> TcPluginM b Source # (<*) :: TcPluginM a -> TcPluginM b -> TcPluginM a Source #
Applicative MetaTyVarUpdateResult Source #
Instance details Defined in GHC.Tc.Utils.Unify Methods pure :: a -> MetaTyVarUpdateResult a Source # (<>) :: MetaTyVarUpdateResult (a -> b) -> MetaTyVarUpdateResult a -> MetaTyVarUpdateResult b Source # liftA2 :: (a -> b -> c) -> MetaTyVarUpdateResult a -> MetaTyVarUpdateResult b -> MetaTyVarUpdateResult c Source # (>) :: MetaTyVarUpdateResult a -> MetaTyVarUpdateResult b -> MetaTyVarUpdateResult b Source # (<*) :: MetaTyVarUpdateResult a -> MetaTyVarUpdateResult b -> MetaTyVarUpdateResult a Source #
Applicative UniqSM Source #
Instance details Defined in GHC.Types.Unique.Supply Methods pure :: a -> UniqSM a Source # (<>) :: UniqSM (a -> b) -> UniqSM a -> UniqSM b Source # liftA2 :: (a -> b -> c) -> UniqSM a -> UniqSM b -> UniqSM c Source # (>) :: UniqSM a -> UniqSM b -> UniqSM b Source # (<*) :: UniqSM a -> UniqSM b -> UniqSM a Source #
Applicative IO	Since: base-2.1
Instance details Defined in GHC.Base Methods pure :: a -> IO a Source # (<>) :: IO (a -> b) -> IO a -> IO b Source # liftA2 :: (a -> b -> c) -> IO a -> IO b -> IO c Source # (>) :: IO a -> IO b -> IO b Source # (<*) :: IO a -> IO b -> IO a Source #
Applicative Q
Instance details Defined in Language.Haskell.TH.Syntax Methods pure :: a -> Q a Source # (<>) :: Q (a -> b) -> Q a -> Q b Source # liftA2 :: (a -> b -> c) -> Q a -> Q b -> Q c Source # (>) :: Q a -> Q b -> Q b Source # (<*) :: Q a -> Q b -> Q a Source #
Applicative Capability
Instance details Defined in System.Console.Terminfo.Base Methods pure :: a -> Capability a Source # (<>) :: Capability (a -> b) -> Capability a -> Capability b Source # liftA2 :: (a -> b -> c) -> Capability a -> Capability b -> Capability c Source # (>) :: Capability a -> Capability b -> Capability b Source # (<*) :: Capability a -> Capability b -> Capability a Source #
Applicative Maybe	Since: base-2.1
Instance details Defined in GHC.Base Methods pure :: a -> Maybe a Source # (<>) :: Maybe (a -> b) -> Maybe a -> Maybe b Source # liftA2 :: (a -> b -> c) -> Maybe a -> Maybe b -> Maybe c Source # (>) :: Maybe a -> Maybe b -> Maybe b Source # (<*) :: Maybe a -> Maybe b -> Maybe a Source #
Applicative Solo	Since: base-4.15
Instance details Defined in GHC.Base Methods pure :: a -> Solo a Source # (<>) :: Solo (a -> b) -> Solo a -> Solo b Source # liftA2 :: (a -> b -> c) -> Solo a -> Solo b -> Solo c Source # (>) :: Solo a -> Solo b -> Solo b Source # (<*) :: Solo a -> Solo b -> Solo a Source #
Applicative []	Since: base-2.1
Instance details Defined in GHC.Base Methods pure :: a -> [a] Source # (<>) :: [a -> b] -> [a] -> [b] Source # liftA2 :: (a -> b -> c) -> [a] -> [b] -> [c] Source # (>) :: [a] -> [b] -> [b] Source # (<*) :: [a] -> [b] -> [a] Source #
Monad m => Applicative (WrappedMonad m)	Since: base-2.1
Instance details Defined in Control.Applicative Methods pure :: a -> WrappedMonad m a Source # (<>) :: WrappedMonad m (a -> b) -> WrappedMonad m a -> WrappedMonad m b Source # liftA2 :: (a -> b -> c) -> WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m c Source # (>) :: WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m b Source # (<*) :: WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m a Source #
Arrow a => Applicative (ArrowMonad a)	Since: base-4.6.0.0
Instance details Defined in Control.Arrow Methods pure :: a0 -> ArrowMonad a a0 Source # (<>) :: ArrowMonad a (a0 -> b) -> ArrowMonad a a0 -> ArrowMonad a b Source # liftA2 :: (a0 -> b -> c) -> ArrowMonad a a0 -> ArrowMonad a b -> ArrowMonad a c Source # (>) :: ArrowMonad a a0 -> ArrowMonad a b -> ArrowMonad a b Source # (<*) :: ArrowMonad a a0 -> ArrowMonad a b -> ArrowMonad a a0 Source #
Applicative (Either e)	Since: base-3.0
Instance details Defined in Data.Either Methods pure :: a -> Either e a Source # (<>) :: Either e (a -> b) -> Either e a -> Either e b Source # liftA2 :: (a -> b -> c) -> Either e a -> Either e b -> Either e c Source # (>) :: Either e a -> Either e b -> Either e b Source # (<*) :: Either e a -> Either e b -> Either e a Source #
Applicative (Proxy :: Type -> Type)	Since: base-4.7.0.0
Instance details Defined in Data.Proxy Methods pure :: a -> Proxy a Source # (<>) :: Proxy (a -> b) -> Proxy a -> Proxy b Source # liftA2 :: (a -> b -> c) -> Proxy a -> Proxy b -> Proxy c Source # (>) :: Proxy a -> Proxy b -> Proxy b Source # (<*) :: Proxy a -> Proxy b -> Proxy a Source #
Applicative (U1 :: Type -> Type)	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods pure :: a -> U1 a Source # (<>) :: U1 (a -> b) -> U1 a -> U1 b Source # liftA2 :: (a -> b -> c) -> U1 a -> U1 b -> U1 c Source # (>) :: U1 a -> U1 b -> U1 b Source # (<*) :: U1 a -> U1 b -> U1 a Source #
Applicative (ST s)	Since: base-4.4.0.0
Instance details Defined in GHC.ST Methods pure :: a -> ST s a Source # (<>) :: ST s (a -> b) -> ST s a -> ST s b Source # liftA2 :: (a -> b -> c) -> ST s a -> ST s b -> ST s c Source # (>) :: ST s a -> ST s b -> ST s b Source # (<*) :: ST s a -> ST s b -> ST s a Source #
Applicative (SetM s)
Instance details Defined in Data.Graph Methods pure :: a -> SetM s a Source # (<>) :: SetM s (a -> b) -> SetM s a -> SetM s b Source # liftA2 :: (a -> b -> c) -> SetM s a -> SetM s b -> SetM s c Source # (>) :: SetM s a -> SetM s b -> SetM s b Source # (<*) :: SetM s a -> SetM s b -> SetM s a Source #
Applicative (RegM freeRegs) Source #
Instance details Defined in GHC.CmmToAsm.Reg.Linear.State Methods pure :: a -> RegM freeRegs a Source # (<>) :: RegM freeRegs (a -> b) -> RegM freeRegs a -> RegM freeRegs b Source # liftA2 :: (a -> b -> c) -> RegM freeRegs a -> RegM freeRegs b -> RegM freeRegs c Source # (>) :: RegM freeRegs a -> RegM freeRegs b -> RegM freeRegs b Source # (<*) :: RegM freeRegs a -> RegM freeRegs b -> RegM freeRegs a Source #
Applicative (IOEnv m) Source #
Instance details Defined in GHC.Data.IOEnv Methods pure :: a -> IOEnv m a Source # (<>) :: IOEnv m (a -> b) -> IOEnv m a -> IOEnv m b Source # liftA2 :: (a -> b -> c) -> IOEnv m a -> IOEnv m b -> IOEnv m c Source # (>) :: IOEnv m a -> IOEnv m b -> IOEnv m b Source # (<*) :: IOEnv m a -> IOEnv m b -> IOEnv m a Source #
Applicative (MaybeErr err) Source #
Instance details Defined in GHC.Data.Maybe Methods pure :: a -> MaybeErr err a Source # (<>) :: MaybeErr err (a -> b) -> MaybeErr err a -> MaybeErr err b Source # liftA2 :: (a -> b -> c) -> MaybeErr err a -> MaybeErr err b -> MaybeErr err c Source # (>) :: MaybeErr err a -> MaybeErr err b -> MaybeErr err b Source # (<*) :: MaybeErr err a -> MaybeErr err b -> MaybeErr err a Source #
Applicative (CmdLineP s) Source #
Instance details Defined in GHC.Driver.CmdLine Methods pure :: a -> CmdLineP s a Source # (<>) :: CmdLineP s (a -> b) -> CmdLineP s a -> CmdLineP s b Source # liftA2 :: (a -> b -> c) -> CmdLineP s a -> CmdLineP s b -> CmdLineP s c Source # (>) :: CmdLineP s a -> CmdLineP s b -> CmdLineP s b Source # (<*) :: CmdLineP s a -> CmdLineP s b -> CmdLineP s a Source #
Monad m => Applicative (EwM m) Source #
Instance details Defined in GHC.Driver.CmdLine Methods pure :: a -> EwM m a Source # (<>) :: EwM m (a -> b) -> EwM m a -> EwM m b Source # liftA2 :: (a -> b -> c) -> EwM m a -> EwM m b -> EwM m c Source # (>) :: EwM m a -> EwM m b -> EwM m b Source # (<*) :: EwM m a -> EwM m b -> EwM m a Source #
Applicative m => Applicative (GhcT m) Source #
Instance details Defined in GHC.Driver.Monad Methods pure :: a -> GhcT m a Source # (<>) :: GhcT m (a -> b) -> GhcT m a -> GhcT m b Source # liftA2 :: (a -> b -> c) -> GhcT m a -> GhcT m b -> GhcT m c Source # (>) :: GhcT m a -> GhcT m b -> GhcT m b Source # (<*) :: GhcT m a -> GhcT m b -> GhcT m a Source #
Applicative (State s) Source #
Instance details Defined in GHC.Utils.Monad.State Methods pure :: a -> State s a Source # (<>) :: State s (a -> b) -> State s a -> State s b Source # liftA2 :: (a -> b -> c) -> State s a -> State s b -> State s c Source # (>) :: State s a -> State s b -> State s b Source # (<*) :: State s a -> State s b -> State s a Source #
Applicative m => Applicative (ListT m)
Instance details Defined in Control.Monad.Trans.List Methods pure :: a -> ListT m a Source # (<>) :: ListT m (a -> b) -> ListT m a -> ListT m b Source # liftA2 :: (a -> b -> c) -> ListT m a -> ListT m b -> ListT m c Source # (>) :: ListT m a -> ListT m b -> ListT m b Source # (<*) :: ListT m a -> ListT m b -> ListT m a Source #
(Functor m, Monad m) => Applicative (MaybeT m)
Instance details Defined in Control.Monad.Trans.Maybe Methods pure :: a -> MaybeT m a Source # (<>) :: MaybeT m (a -> b) -> MaybeT m a -> MaybeT m b Source # liftA2 :: (a -> b -> c) -> MaybeT m a -> MaybeT m b -> MaybeT m c Source # (>) :: MaybeT m a -> MaybeT m b -> MaybeT m b Source # (<*) :: MaybeT m a -> MaybeT m b -> MaybeT m a Source #
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) Source # (<>) :: (a, a0 -> b) -> (a, a0) -> (a, b) Source # liftA2 :: (a0 -> b -> c) -> (a, a0) -> (a, b) -> (a, c) Source # (>) :: (a, a0) -> (a, b) -> (a, b) Source # (<*) :: (a, a0) -> (a, b) -> (a, a0) Source #
Arrow a => Applicative (WrappedArrow a b)	Since: base-2.1
Instance details Defined in Control.Applicative Methods pure :: a0 -> WrappedArrow a b a0 Source # (<>) :: WrappedArrow a b (a0 -> b0) -> WrappedArrow a b a0 -> WrappedArrow a b b0 Source # liftA2 :: (a0 -> b0 -> c) -> WrappedArrow a b a0 -> WrappedArrow a b b0 -> WrappedArrow a b c Source # (>) :: WrappedArrow a b a0 -> WrappedArrow a b b0 -> WrappedArrow a b b0 Source # (<*) :: WrappedArrow a b a0 -> WrappedArrow a b b0 -> WrappedArrow a b a0 Source #
Applicative m => Applicative (Kleisli m a)	Since: base-4.14.0.0
Instance details Defined in Control.Arrow Methods pure :: a0 -> Kleisli m a a0 Source # (<>) :: Kleisli m a (a0 -> b) -> Kleisli m a a0 -> Kleisli m a b Source # liftA2 :: (a0 -> b -> c) -> Kleisli m a a0 -> Kleisli m a b -> Kleisli m a c Source # (>) :: Kleisli m a a0 -> Kleisli m a b -> Kleisli m a b Source # (<*) :: Kleisli m a a0 -> Kleisli m a b -> Kleisli m a a0 Source #
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 Source # (<>) :: Const m (a -> b) -> Const m a -> Const m b Source # liftA2 :: (a -> b -> c) -> Const m a -> Const m b -> Const m c Source # (>) :: Const m a -> Const m b -> Const m b Source # (<*) :: Const m a -> Const m b -> Const m a Source #
Applicative f => Applicative (Ap f)	Since: base-4.12.0.0
Instance details Defined in Data.Monoid Methods pure :: a -> Ap f a Source # (<>) :: Ap f (a -> b) -> Ap f a -> Ap f b Source # liftA2 :: (a -> b -> c) -> Ap f a -> Ap f b -> Ap f c Source # (>) :: Ap f a -> Ap f b -> Ap f b Source # (<*) :: Ap f a -> Ap f b -> Ap f a Source #
Applicative f => Applicative (Alt f)	Since: base-4.8.0.0
Instance details Defined in Data.Semigroup.Internal Methods pure :: a -> Alt f a Source # (<>) :: Alt f (a -> b) -> Alt f a -> Alt f b Source # liftA2 :: (a -> b -> c) -> Alt f a -> Alt f b -> Alt f c Source # (>) :: Alt f a -> Alt f b -> Alt f b Source # (<*) :: Alt f a -> Alt f b -> Alt f a Source #
Applicative f => Applicative (Rec1 f)	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods pure :: a -> Rec1 f a Source # (<>) :: Rec1 f (a -> b) -> Rec1 f a -> Rec1 f b Source # liftA2 :: (a -> b -> c) -> Rec1 f a -> Rec1 f b -> Rec1 f c Source # (>) :: Rec1 f a -> Rec1 f b -> Rec1 f b Source # (<*) :: Rec1 f a -> Rec1 f b -> Rec1 f a Source #
(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 Source # (<>) :: WhenMissing f x (a -> b) -> WhenMissing f x a -> WhenMissing f x b Source # liftA2 :: (a -> b -> c) -> WhenMissing f x a -> WhenMissing f x b -> WhenMissing f x c Source # (>) :: WhenMissing f x a -> WhenMissing f x b -> WhenMissing f x b Source # (<*) :: WhenMissing f x a -> WhenMissing f x b -> WhenMissing f x a Source #
Monad m => Applicative (Stream m a) Source #
Instance details Defined in GHC.Data.Stream Methods pure :: a0 -> Stream m a a0 Source # (<>) :: Stream m a (a0 -> b) -> Stream m a a0 -> Stream m a b Source # liftA2 :: (a0 -> b -> c) -> Stream m a a0 -> Stream m a b -> Stream m a c Source # (>) :: Stream m a a0 -> Stream m a b -> Stream m a b Source # (<*) :: Stream m a a0 -> Stream m a b -> Stream m a a0 Source #
(Functor m, Monad m) => Applicative (ErrorT e m)
Instance details Defined in Control.Monad.Trans.Error Methods pure :: a -> ErrorT e m a Source # (<>) :: ErrorT e m (a -> b) -> ErrorT e m a -> ErrorT e m b Source # liftA2 :: (a -> b -> c) -> ErrorT e m a -> ErrorT e m b -> ErrorT e m c Source # (>) :: ErrorT e m a -> ErrorT e m b -> ErrorT e m b Source # (<*) :: ErrorT e m a -> ErrorT e m b -> ErrorT e m a Source #
(Functor m, Monad m) => Applicative (ExceptT e m)
Instance details Defined in Control.Monad.Trans.Except Methods pure :: a -> ExceptT e m a Source # (<>) :: ExceptT e m (a -> b) -> ExceptT e m a -> ExceptT e m b Source # liftA2 :: (a -> b -> c) -> ExceptT e m a -> ExceptT e m b -> ExceptT e m c Source # (>) :: ExceptT e m a -> ExceptT e m b -> ExceptT e m b Source # (<*) :: ExceptT e m a -> ExceptT e m b -> ExceptT e m a Source #
Applicative m => Applicative (IdentityT m)
Instance details Defined in Control.Monad.Trans.Identity Methods pure :: a -> IdentityT m a Source # (<>) :: IdentityT m (a -> b) -> IdentityT m a -> IdentityT m b Source # liftA2 :: (a -> b -> c) -> IdentityT m a -> IdentityT m b -> IdentityT m c Source # (>) :: IdentityT m a -> IdentityT m b -> IdentityT m b Source # (<*) :: IdentityT m a -> IdentityT m b -> IdentityT m a Source #
Applicative m => Applicative (ReaderT r m)
Instance details Defined in Control.Monad.Trans.Reader Methods pure :: a -> ReaderT r m a Source # (<>) :: ReaderT r m (a -> b) -> ReaderT r m a -> ReaderT r m b Source # liftA2 :: (a -> b -> c) -> ReaderT r m a -> ReaderT r m b -> ReaderT r m c Source # (>) :: ReaderT r m a -> ReaderT r m b -> ReaderT r m b Source # (<*) :: ReaderT r m a -> ReaderT r m b -> ReaderT r m a Source #
(Functor m, Monad m) => Applicative (StateT s m)
Instance details Defined in Control.Monad.Trans.State.Lazy Methods pure :: a -> StateT s m a Source # (<>) :: StateT s m (a -> b) -> StateT s m a -> StateT s m b Source # liftA2 :: (a -> b -> c) -> StateT s m a -> StateT s m b -> StateT s m c Source # (>) :: StateT s m a -> StateT s m b -> StateT s m b Source # (<*) :: StateT s m a -> StateT s m b -> StateT s m a Source #
(Functor m, Monad m) => Applicative (StateT s m)
Instance details Defined in Control.Monad.Trans.State.Strict Methods pure :: a -> StateT s m a Source # (<>) :: StateT s m (a -> b) -> StateT s m a -> StateT s m b Source # liftA2 :: (a -> b -> c) -> StateT s m a -> StateT s m b -> StateT s m c Source # (>) :: StateT s m a -> StateT s m b -> StateT s m b Source # (<*) :: StateT s m a -> StateT s m b -> StateT s m a Source #
(Monoid w, Applicative m) => Applicative (WriterT w m)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods pure :: a -> WriterT w m a Source # (<>) :: WriterT w m (a -> b) -> WriterT w m a -> WriterT w m b Source # liftA2 :: (a -> b -> c) -> WriterT w m a -> WriterT w m b -> WriterT w m c Source # (>) :: WriterT w m a -> WriterT w m b -> WriterT w m b Source # (<*) :: WriterT w m a -> WriterT w m b -> WriterT w m a Source #
(Monoid w, Applicative m) => Applicative (WriterT w m)
Instance details Defined in Control.Monad.Trans.Writer.Strict Methods pure :: a -> WriterT w m a Source # (<>) :: WriterT w m (a -> b) -> WriterT w m a -> WriterT w m b Source # liftA2 :: (a -> b -> c) -> WriterT w m a -> WriterT w m b -> WriterT w m c Source # (>) :: WriterT w m a -> WriterT w m b -> WriterT w m b Source # (<*) :: WriterT w m a -> WriterT w m b -> WriterT w m a Source #
(Monoid a, Monoid b) => Applicative ((,,) a b)	Since: base-4.14.0.0
Instance details Defined in GHC.Base Methods pure :: a0 -> (a, b, a0) Source # (<>) :: (a, b, a0 -> b0) -> (a, b, a0) -> (a, b, b0) Source # liftA2 :: (a0 -> b0 -> c) -> (a, b, a0) -> (a, b, b0) -> (a, b, c) Source # (>) :: (a, b, a0) -> (a, b, b0) -> (a, b, b0) Source # (<*) :: (a, b, a0) -> (a, b, b0) -> (a, b, a0) Source #
(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 Source # (<>) :: Product f g (a -> b) -> Product f g a -> Product f g b Source # liftA2 :: (a -> b -> c) -> Product f g a -> Product f g b -> Product f g c Source # (>) :: Product f g a -> Product f g b -> Product f g b Source # (<*) :: Product f g a -> Product f g b -> Product f g a Source #
(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 Source # (<>) :: (f :: g) (a -> b) -> (f :: g) a -> (f :: g) b Source # liftA2 :: (a -> b -> c) -> (f :: g) a -> (f :: g) b -> (f :: g) c Source # (>) :: (f :: g) a -> (f :: g) b -> (f :: g) b Source # (<) :: (f :: g) a -> (f :: g) b -> (f :: g) a Source #
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 Source # (<>) :: K1 i c (a -> b) -> K1 i c a -> K1 i c b Source # liftA2 :: (a -> b -> c0) -> K1 i c a -> K1 i c b -> K1 i c c0 Source # (>) :: K1 i c a -> K1 i c b -> K1 i c b Source # (<*) :: K1 i c a -> K1 i c b -> K1 i c a Source #
(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 Source # (<>) :: WhenMatched f x y (a -> b) -> WhenMatched f x y a -> WhenMatched f x y b Source # liftA2 :: (a -> b -> c) -> WhenMatched f x y a -> WhenMatched f x y b -> WhenMatched f x y c Source # (>) :: WhenMatched f x y a -> WhenMatched f x y b -> WhenMatched f x y b Source # (<*) :: WhenMatched f x y a -> WhenMatched f x y b -> WhenMatched f x y a Source #
(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 Source # (<>) :: WhenMissing f k x (a -> b) -> WhenMissing f k x a -> WhenMissing f k x b Source # liftA2 :: (a -> b -> c) -> WhenMissing f k x a -> WhenMissing f k x b -> WhenMissing f k x c Source # (>) :: WhenMissing f k x a -> WhenMissing f k x b -> WhenMissing f k x b Source # (<*) :: WhenMissing f k x a -> WhenMissing f k x b -> WhenMissing f k x a Source #
Applicative (ContT r m)
Instance details Defined in Control.Monad.Trans.Cont Methods pure :: a -> ContT r m a Source # (<>) :: ContT r m (a -> b) -> ContT r m a -> ContT r m b Source # liftA2 :: (a -> b -> c) -> ContT r m a -> ContT r m b -> ContT r m c Source # (>) :: ContT r m a -> ContT r m b -> ContT r m b Source # (<*) :: ContT r m a -> ContT r m b -> ContT r m a Source #
(Monoid a, Monoid b, Monoid c) => Applicative ((,,,) a b c)	Since: base-4.14.0.0
Instance details Defined in GHC.Base Methods pure :: a0 -> (a, b, c, a0) Source # (<>) :: (a, b, c, a0 -> b0) -> (a, b, c, a0) -> (a, b, c, b0) Source # liftA2 :: (a0 -> b0 -> c0) -> (a, b, c, a0) -> (a, b, c, b0) -> (a, b, c, c0) Source # (>) :: (a, b, c, a0) -> (a, b, c, b0) -> (a, b, c, b0) Source # (<*) :: (a, b, c, a0) -> (a, b, c, b0) -> (a, b, c, a0) Source #
Applicative ((->) r)	Since: base-2.1
Instance details Defined in GHC.Base Methods pure :: a -> r -> a Source # (<>) :: (r -> (a -> b)) -> (r -> a) -> r -> b Source # liftA2 :: (a -> b -> c) -> (r -> a) -> (r -> b) -> r -> c Source # (>) :: (r -> a) -> (r -> b) -> r -> b Source # (<*) :: (r -> a) -> (r -> b) -> r -> a Source #
(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 Source # (<>) :: Compose f g (a -> b) -> Compose f g a -> Compose f g b Source # liftA2 :: (a -> b -> c) -> Compose f g a -> Compose f g b -> Compose f g c Source # (>) :: Compose f g a -> Compose f g b -> Compose f g b Source # (<*) :: Compose f g a -> Compose f g b -> Compose f g a Source #
(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 Source # (<>) :: (f :.: g) (a -> b) -> (f :.: g) a -> (f :.: g) b Source # liftA2 :: (a -> b -> c) -> (f :.: g) a -> (f :.: g) b -> (f :.: g) c Source # (>) :: (f :.: g) a -> (f :.: g) b -> (f :.: g) b Source # (<*) :: (f :.: g) a -> (f :.: g) b -> (f :.: g) a Source #
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 Source # (<>) :: M1 i c f (a -> b) -> M1 i c f a -> M1 i c f b Source # liftA2 :: (a -> b -> c0) -> M1 i c f a -> M1 i c f b -> M1 i c f c0 Source # (>) :: M1 i c f a -> M1 i c f b -> M1 i c f b Source # (<*) :: M1 i c f a -> M1 i c f b -> M1 i c f a Source #
(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 Source # (<>) :: WhenMatched f k x y (a -> b) -> WhenMatched f k x y a -> WhenMatched f k x y b Source # liftA2 :: (a -> b -> c) -> WhenMatched f k x y a -> WhenMatched f k x y b -> WhenMatched f k x y c Source # (>) :: WhenMatched f k x y a -> WhenMatched f k x y b -> WhenMatched f k x y b Source # (<*) :: WhenMatched f k x y a -> WhenMatched f k x y b -> WhenMatched f k x y a Source #
(Functor m, Monad m) => Applicative (RWST r w s m)
Instance details Defined in Control.Monad.Trans.RWS.CPS Methods pure :: a -> RWST r w s m a Source # (<>) :: RWST r w s m (a -> b) -> RWST r w s m a -> RWST r w s m b Source # liftA2 :: (a -> b -> c) -> RWST r w s m a -> RWST r w s m b -> RWST r w s m c Source # (>) :: RWST r w s m a -> RWST r w s m b -> RWST r w s m b Source # (<*) :: RWST r w s m a -> RWST r w s m b -> RWST r w s m a Source #
(Monoid w, Functor m, Monad m) => Applicative (RWST r w s m)
Instance details Defined in Control.Monad.Trans.RWS.Lazy Methods pure :: a -> RWST r w s m a Source # (<>) :: RWST r w s m (a -> b) -> RWST r w s m a -> RWST r w s m b Source # liftA2 :: (a -> b -> c) -> RWST r w s m a -> RWST r w s m b -> RWST r w s m c Source # (>) :: RWST r w s m a -> RWST r w s m b -> RWST r w s m b Source # (<*) :: RWST r w s m a -> RWST r w s m b -> RWST r w s m a Source #
(Monoid w, Functor m, Monad m) => Applicative (RWST r w s m)
Instance details Defined in Control.Monad.Trans.RWS.Strict Methods pure :: a -> RWST r w s m a Source # (<>) :: RWST r w s m (a -> b) -> RWST r w s m a -> RWST r w s m b Source # liftA2 :: (a -> b -> c) -> RWST r w s m a -> RWST r w s m b -> RWST r w s m c Source # (>) :: RWST r w s m a -> RWST r w s m b -> RWST r w s m b Source # (<*) :: RWST r w s m a -> RWST r w s m b -> RWST r w s m a Source #

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

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 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

Instances details

MonadFix Complex	Since: base-4.15.0.0
Instance details Defined in Data.Complex Methods mfix :: (a -> Complex a) -> Complex a Source #
MonadFix Identity	Since: base-4.8.0.0
Instance details Defined in Data.Functor.Identity Methods mfix :: (a -> Identity a) -> Identity a Source #
MonadFix First	Since: base-4.8.0.0
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> First a) -> First a Source #
MonadFix Last	Since: base-4.8.0.0
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> Last a) -> Last a Source #
MonadFix Down	Since: base-4.12.0.0
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> Down a) -> Down a Source #
MonadFix First	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods mfix :: (a -> First a) -> First a Source #
MonadFix Last	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods mfix :: (a -> Last a) -> Last a Source #
MonadFix Max	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods mfix :: (a -> Max a) -> Max a Source #
MonadFix Min	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods mfix :: (a -> Min a) -> Min a Source #
MonadFix Option	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods mfix :: (a -> Option a) -> Option a Source #
MonadFix Dual	Since: base-4.8.0.0
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> Dual a) -> Dual a Source #
MonadFix Product	Since: base-4.8.0.0
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> Product a) -> Product a Source #
MonadFix Sum	Since: base-4.8.0.0
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> Sum a) -> Sum a Source #
MonadFix NonEmpty	Since: base-4.9.0.0
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> NonEmpty a) -> NonEmpty a Source #
MonadFix Par1	Since: base-4.9.0.0
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> Par1 a) -> Par1 a Source #
MonadFix Seq	Since: containers-0.5.11
Instance details Defined in Data.Sequence.Internal Methods mfix :: (a -> Seq a) -> Seq a Source #
MonadFix Tree	Since: containers-0.5.11
Instance details Defined in Data.Tree Methods mfix :: (a -> Tree a) -> Tree a Source #
MonadFix Ghc Source #
Instance details Defined in GHC.Driver.Monad Methods mfix :: (a -> Ghc a) -> Ghc a Source #
MonadFix UniqSM Source #
Instance details Defined in GHC.Types.Unique.Supply Methods mfix :: (a -> UniqSM a) -> UniqSM a Source #
MonadFix IO	Since: base-2.1
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> IO a) -> IO a Source #
MonadFix Q	If the function passed to `mfix` inspects its argument, the resulting action will throw a `FixIOException`. Since: template-haskell-2.17.0.0
Instance details Defined in Language.Haskell.TH.Syntax Methods mfix :: (a -> Q a) -> Q a Source #
MonadFix Maybe	Since: base-2.1
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> Maybe a) -> Maybe a Source #
MonadFix Solo	Since: base-4.15
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> Solo a) -> Solo a Source #
MonadFix []	Since: base-2.1
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> [a]) -> [a] Source #
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 Source #
MonadFix (ST s)	Since: base-2.1
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> ST s a) -> ST s a Source #
MonadFix m => MonadFix (ListT m)
Instance details Defined in Control.Monad.Trans.List Methods mfix :: (a -> ListT m a) -> ListT m a Source #
MonadFix m => MonadFix (MaybeT m)
Instance details Defined in Control.Monad.Trans.Maybe Methods mfix :: (a -> MaybeT m a) -> MaybeT m a Source #
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 Source #
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 Source #
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 Source #
(MonadFix m, Error e) => MonadFix (ErrorT e m)
Instance details Defined in Control.Monad.Trans.Error Methods mfix :: (a -> ErrorT e m a) -> ErrorT e m a Source #
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 Source #
MonadFix m => MonadFix (IdentityT m)
Instance details Defined in Control.Monad.Trans.Identity Methods mfix :: (a -> IdentityT m a) -> IdentityT m a Source #
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 Source #
MonadFix m => MonadFix (StateT s m)
Instance details Defined in Control.Monad.Trans.State.Lazy Methods mfix :: (a -> StateT s m a) -> StateT s m a Source #
MonadFix m => MonadFix (StateT s m)
Instance details Defined in Control.Monad.Trans.State.Strict Methods mfix :: (a -> StateT s m a) -> StateT s m a Source #
(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 Source #
(Monoid w, MonadFix m) => MonadFix (WriterT w m)
Instance details Defined in Control.Monad.Trans.Writer.Strict Methods mfix :: (a -> WriterT w m a) -> WriterT w m a Source #
(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 Source #
(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 Source #
MonadFix ((->) r)	Since: base-2.1
Instance details Defined in Control.Monad.Fix Methods mfix :: (a -> r -> a) -> r -> a Source #
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 Source #
MonadFix m => MonadFix (RWST r w s m)
Instance details Defined in Control.Monad.Trans.RWS.CPS Methods mfix :: (a -> RWST r w s m a) -> RWST r w s m a Source #
(Monoid w, MonadFix m) => MonadFix (RWST r w s m)
Instance details Defined in Control.Monad.Trans.RWS.Lazy Methods mfix :: (a -> RWST r w s m a) -> RWST r w s m a Source #
(Monoid w, MonadFix m) => MonadFix (RWST r w s m)
Instance details Defined in Control.Monad.Trans.RWS.Strict Methods mfix :: (a -> RWST r w s m a) -> RWST r w s m a Source #

class Monad m => MonadIO (m :: Type -> Type) 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. This allows us to run IO computations in any monadic stack, so long as it supports these kinds of operations (i.e. IO is the base monad for the stack).

Example

Expand

import Control.Monad.Trans.State -- from the "transformers" library

printState :: Show s => StateT s IO ()
printState = do
  state <- get
  liftIO $ print state

Had we omitted liftIO, we would have ended up with this error:

• Couldn't match type ‘IO’ with ‘StateT s IO’
 Expected type: StateT s IO ()
   Actual type: IO ()

The important part here is the mismatch between StateT s IO () and IO ().

Luckily, we know of a function that takes an IO a and returns an (m a): liftIO, enabling us to run the program and see the expected results:

> evalStateT printState "hello"
"hello"

> evalStateT printState 3
3

Instances

Instances details

MonadIO CoreM Source #
Instance details Defined in GHC.Core.Opt.Monad Methods liftIO :: IO a -> CoreM a Source #
MonadIO SimplM Source #
Instance details Defined in GHC.Core.Opt.Simplify.Monad Methods liftIO :: IO a -> SimplM a Source #
MonadIO Ghc Source #
Instance details Defined in GHC.Driver.Monad Methods liftIO :: IO a -> Ghc a Source #
MonadIO CompPipeline Source #
Instance details Defined in GHC.Driver.Pipeline.Monad Methods liftIO :: IO a -> CompPipeline a Source #
MonadIO Hsc Source #
Instance details Defined in GHC.Driver.Types Methods liftIO :: IO a -> Hsc a Source #
MonadIO IO	Since: base-4.9.0.0
Instance details Defined in Control.Monad.IO.Class Methods liftIO :: IO a -> IO a Source #
MonadIO Q
Instance details Defined in Language.Haskell.TH.Syntax Methods liftIO :: IO a -> Q a Source #
MonadIO (IOEnv env) Source #
Instance details Defined in GHC.Data.IOEnv Methods liftIO :: IO a -> IOEnv env a Source #
MonadIO m => MonadIO (GhcT m) Source #
Instance details Defined in GHC.Driver.Monad Methods liftIO :: IO a -> GhcT m a Source #
MonadIO m => MonadIO (ListT m)
Instance details Defined in Control.Monad.Trans.List Methods liftIO :: IO a -> ListT m a Source #
MonadIO m => MonadIO (MaybeT m)
Instance details Defined in Control.Monad.Trans.Maybe Methods liftIO :: IO a -> MaybeT m a Source #
(Error e, MonadIO m) => MonadIO (ErrorT e m)
Instance details Defined in Control.Monad.Trans.Error Methods liftIO :: IO a -> ErrorT e m a Source #
MonadIO m => MonadIO (ExceptT e m)
Instance details Defined in Control.Monad.Trans.Except Methods liftIO :: IO a -> ExceptT e m a Source #
MonadIO m => MonadIO (IdentityT m)
Instance details Defined in Control.Monad.Trans.Identity Methods liftIO :: IO a -> IdentityT m a Source #
MonadIO m => MonadIO (ReaderT r m)
Instance details Defined in Control.Monad.Trans.Reader Methods liftIO :: IO a -> ReaderT r m a Source #
MonadIO m => MonadIO (StateT s m)
Instance details Defined in Control.Monad.Trans.State.Lazy Methods liftIO :: IO a -> StateT s m a Source #
MonadIO m => MonadIO (StateT s m)
Instance details Defined in Control.Monad.Trans.State.Strict Methods liftIO :: IO a -> StateT s m a Source #
(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 Source #
(Monoid w, MonadIO m) => MonadIO (WriterT w m)
Instance details Defined in Control.Monad.Trans.Writer.Strict Methods liftIO :: IO a -> WriterT w m a Source #
MonadIO m => MonadIO (ContT r m)
Instance details Defined in Control.Monad.Trans.Cont Methods liftIO :: IO a -> ContT r m a Source #
MonadIO m => MonadIO (RWST r w s m)
Instance details Defined in Control.Monad.Trans.RWS.CPS Methods liftIO :: IO a -> RWST r w s m a Source #
(Monoid w, MonadIO m) => MonadIO (RWST r w s m)
Instance details Defined in Control.Monad.Trans.RWS.Lazy Methods liftIO :: IO a -> RWST r w s m a Source #
(Monoid w, MonadIO m) => MonadIO (RWST r w s m)
Instance details Defined in Control.Monad.Trans.RWS.Strict Methods liftIO :: IO a -> RWST r w s m a Source #

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]) 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 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 Source #

Left-to-right monadic fold over the elements of a structure.

Given a structure t with elements (a, b, ..., w, x, y), the result of a fold with an operator function f is equivalent to:

foldlM f z t = do
    aa <- f z a
    bb <- f aa b
    ...
    xx <- f ww x
    yy <- f xx y
    return yy -- Just @return z@ when the structure is empty

For a Monad m, given two functions f1 :: a -> m b and f2 :: b -> m c, their Kleisli composition (f1 >=> f2) :: a -> m c is defined by:

(f1 >=> f2) a = f1 a >>= f2

Another way of thinking about foldlM is that it amounts to an application to z of a Kleisli composition:

foldlM f z t =
    flip f a >=> flip f b >=> ... >=> flip f x >=> flip f y $ z

The monadic effects of foldlM are sequenced from left to right.

If at some step the bind operator (>>=) short-circuits (as with, e.g., mzero in a MonadPlus), the evaluated effects will be from an initial segment of the element sequence. If you want to evaluate the monadic effects in right-to-left order, or perhaps be able to short-circuit after processing a tail of the sequence of elements, you'll need to use foldrM instead.

If the monadic effects don't short-circuit, the outermost application of f is to the rightmost element y, so that, ignoring effects, the result looks like a left fold:

((((z `f` a) `f` b) ... `f` w) `f` x) `f` y

Examples

Expand

Basic usage:

>>> let f a e = do { print e ; return $ e : a }
>>> foldlM f [] [0..3]
0
1
2
3
[3,2,1,0]

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 Source #

Right-to-left monadic fold over the elements of a structure.

Given a structure t with elements (a, b, c, ..., x, y), the result of a fold with an operator function f is equivalent to:

foldrM f z t = do
    yy <- f y z
    xx <- f x yy
    ...
    bb <- f b cc
    aa <- f a bb
    return aa -- Just @return z@ when the structure is empty

For a Monad m, given two functions f1 :: a -> m b and f2 :: b -> m c, their Kleisli composition (f1 >=> f2) :: a -> m c is defined by:

(f1 >=> f2) a = f1 a >>= f2

Another way of thinking about foldrM is that it amounts to an application to z of a Kleisli composition:

foldrM f z t = f y >=> f x >=> ... >=> f b >=> f a $ z

The monadic effects of foldrM are sequenced from right to left, and e.g. folds of infinite lists will diverge.

If at some step the bind operator (>>=) short-circuits (as with, e.g., mzero in a MonadPlus), the evaluated effects will be from a tail of the element sequence. If you want to evaluate the monadic effects in left-to-right order, or perhaps be able to short-circuit after an initial sequence of elements, you'll need to use foldlM instead.

If the monadic effects don't short-circuit, the outermost application of f is to the leftmost element a, so that, ignoring effects, the result looks like a right fold:

a `f` (b `f` (c `f` (... (x `f` (y `f` z))))).

Examples

Expand

Basic usage:

>>> let f i acc = do { print i ; return $ i : acc }
>>> foldrM f [] [0..3]
3
2
1
0
[0,1,2,3]

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.