Copyright | Conor McBride and Ross Paterson 2005 |
---|---|
License | BSD-style (see the LICENSE file in the distribution) |
Maintainer | libraries@haskell.org |
Stability | stable |
Portability | portable |
Safe Haskell | Trustworthy |
Language | Haskell2010 |
Control.Applicative
Description
This module describes a structure intermediate between a functor and
a monad (technically, a strong lax monoidal functor). Compared with
monads, this interface lacks the full power of the binding operation
>>=
, but
- it has more instances.
- it is sufficient for many uses, e.g. context-free parsing, or the
Traversable
class. - instances can perform analysis of computations before they are executed, and thus produce shared optimizations.
This interface was introduced for parsers by Niklas Röjemo, because it admits more sharing than the monadic interface. The names here are mostly based on parsing work by Doaitse Swierstra.
For more details, see Applicative Programming with Effects, by Conor McBride and Ross Paterson.
Synopsis
- class Functor f => Applicative f where
- class Applicative f => Alternative f where
- newtype Const a b = Const {
- getConst :: a
- newtype WrappedMonad m a = WrapMonad {
- unwrapMonad :: m a
- newtype WrappedArrow a b c = WrapArrow {
- unwrapArrow :: a b c
- newtype ZipList a = ZipList {
- getZipList :: [a]
- (<$>) :: Functor f => (a -> b) -> f a -> f b
- (<$) :: Functor f => a -> f b -> f a
- (<**>) :: Applicative f => f a -> f (a -> b) -> f b
- liftA :: Applicative f => (a -> b) -> f a -> f b
- liftA3 :: Applicative f => (a -> b -> c -> d) -> f a -> f b -> f c -> f d
- optional :: Alternative f => f a -> f (Maybe a)
- asum :: (Foldable t, Alternative f) => t (f a) -> f a
Applicative functors
class Functor f => Applicative f where Source #
A functor with application, providing operations to
- embed pure expressions (
pure
), and - sequence computations and combine their results (
<*>
andliftA2
).
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:
As a consequence of these laws, the Functor
instance for f
will satisfy
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
(which implies that pure
and <*>
satisfy the applicative functor laws).
Methods
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
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
Instance details
Defined in Data.Complex
Instance details
Defined in Data.Functor.Identity
Instance details
Defined in Data.Semigroup.Internal
Instance details
Defined in GHC.Base
Instance details
Defined in Text.ParserCombinators.ReadP
Instance details
Defined in Text.ParserCombinators.ReadPrec
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 #
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 #
Instance details
Defined in Data.Either
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 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 #
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 #
Instance details
Defined in Data.Functor.Const
Instance details
Defined in Data.Semigroup.Internal
Instance details
Defined in GHC.Generics
Methods
pure :: a -> Generically1 f a Source #
(<*>) :: Generically1 f (a -> b) -> Generically1 f a -> Generically1 f b Source #
liftA2 :: (a -> b -> c) -> Generically1 f a -> Generically1 f b -> Generically1 f c Source #
(*>) :: Generically1 f a -> Generically1 f b -> Generically1 f b Source #
(<*) :: Generically1 f a -> Generically1 f b -> Generically1 f a Source #
Instance details
Defined in GHC.Generics
Instance details
Defined in GHC.Base
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 #
Instance details
Defined in GHC.Generics
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 #
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 #
Instance details
Defined in GHC.Generics
Alternatives
class Applicative f => Alternative f where Source #
A monoid on applicative functors.
If defined, some
and many
should be the least solutions
of the equations:
Methods
The identity of <|>
(<|>) :: f a -> f a -> f a infixl 3 Source #
An associative binary operation
One or more.
Zero or more.
Instances
Instances details
Takes the first non-throwing IO
action's result.
empty
throws an exception.
Since: base-4.9.0.0
Picks the leftmost Just
value, or, alternatively, Nothing
.
Since: base-2.1
Combines lists by concatenation, starting from the empty list.
Since: base-2.1
Instance details
Defined in Control.Applicative
Methods
empty :: WrappedMonad m a Source #
(<|>) :: WrappedMonad m a -> WrappedMonad m a -> WrappedMonad m a Source #
some :: WrappedMonad m a -> WrappedMonad m [a] Source #
many :: WrappedMonad m a -> WrappedMonad m [a] Source #
Instance details
Defined in Control.Arrow
Methods
empty :: ArrowMonad a a0 Source #
(<|>) :: ArrowMonad a a0 -> ArrowMonad a a0 -> ArrowMonad a a0 Source #
some :: ArrowMonad a a0 -> ArrowMonad a [a0] Source #
many :: ArrowMonad a a0 -> ArrowMonad a [a0] Source #
Instance details
Defined in Control.Applicative
Methods
empty :: WrappedArrow a b a0 Source #
(<|>) :: WrappedArrow a b a0 -> WrappedArrow a b a0 -> WrappedArrow a b a0 Source #
some :: WrappedArrow a b a0 -> WrappedArrow a b [a0] Source #
many :: WrappedArrow a b a0 -> WrappedArrow a b [a0] Source #
Instance details
Defined in GHC.Generics
Methods
empty :: Generically1 f a Source #
(<|>) :: Generically1 f a -> Generically1 f a -> Generically1 f a Source #
some :: Generically1 f a -> Generically1 f [a] Source #
many :: Generically1 f a -> Generically1 f [a] Source #
Instances
The Const
functor.
Instances
Instances details
Instance details
Defined in Data.Bifoldable
Instance details
Defined in Data.Bitraversable
Methods
bitraverse :: Applicative f => (a -> f c) -> (b -> f d) -> Const a b -> f (Const c d) Source #
Instance details
Defined in Data.Functor.Classes
Instance details
Defined in Data.Functor.Classes
Methods
liftReadsPrec2 :: (Int -> ReadS a) -> ReadS [a] -> (Int -> ReadS b) -> ReadS [b] -> Int -> ReadS (Const a b) Source #
liftReadList2 :: (Int -> ReadS a) -> ReadS [a] -> (Int -> ReadS b) -> ReadS [b] -> ReadS [Const a b] Source #
liftReadPrec2 :: ReadPrec a -> ReadPrec [a] -> ReadPrec b -> ReadPrec [b] -> ReadPrec (Const a b) Source #
liftReadListPrec2 :: ReadPrec a -> ReadPrec [a] -> ReadPrec b -> ReadPrec [b] -> ReadPrec [Const a b] Source #
Instance details
Defined in Data.Functor.Classes
Instance details
Defined in Data.Functor.Const
Methods
fold :: Monoid m0 => Const m m0 -> m0 Source #
foldMap :: Monoid m0 => (a -> m0) -> Const m a -> m0 Source #
foldMap' :: Monoid m0 => (a -> m0) -> Const m a -> m0 Source #
foldr :: (a -> b -> b) -> b -> Const m a -> b Source #
foldr' :: (a -> b -> b) -> b -> Const m a -> b Source #
foldl :: (b -> a -> b) -> b -> Const m a -> b Source #
foldl' :: (b -> a -> b) -> b -> Const m a -> b Source #
foldr1 :: (a -> a -> a) -> Const m a -> a Source #
foldl1 :: (a -> a -> a) -> Const m a -> a Source #
toList :: Const m a -> [a] Source #
null :: Const m a -> Bool Source #
length :: Const m a -> Int Source #
elem :: Eq a => a -> Const m a -> Bool Source #
maximum :: Ord a => Const m a -> a Source #
minimum :: Ord a => Const m a -> a Source #
Instance details
Defined in Data.Functor.Classes
Instance details
Defined in Data.Functor.Classes
Methods
liftReadsPrec :: (Int -> ReadS a0) -> ReadS [a0] -> Int -> ReadS (Const a a0) Source #
liftReadList :: (Int -> ReadS a0) -> ReadS [a0] -> ReadS [Const a a0] Source #
liftReadPrec :: ReadPrec a0 -> ReadPrec [a0] -> ReadPrec (Const a a0) Source #
liftReadListPrec :: ReadPrec a0 -> ReadPrec [a0] -> ReadPrec [Const a a0] Source #
Instance details
Defined in Data.Traversable
Instance details
Defined in Data.Functor.Const
Instance details
Defined in Data.Data
Methods
gfoldl :: (forall d b0. Data d => c (d -> b0) -> d -> c b0) -> (forall g. g -> c g) -> Const a b -> c (Const a b) Source #
gunfold :: (forall b0 r. Data b0 => c (b0 -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (Const a b) Source #
toConstr :: Const a b -> Constr Source #
dataTypeOf :: Const a b -> DataType Source #
dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (Const a b)) Source #
dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (Const a b)) Source #
gmapT :: (forall b0. Data b0 => b0 -> b0) -> Const a b -> Const a b Source #
gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Const a b -> r Source #
gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Const a b -> r Source #
gmapQ :: (forall d. Data d => d -> u) -> Const a b -> [u] Source #
gmapQi :: Int -> (forall d. Data d => d -> u) -> Const a b -> u Source #
gmapM :: Monad m => (forall d. Data d => d -> m d) -> Const a b -> m (Const a b) Source #
gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Const a b -> m (Const a b) Source #
gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Const a b -> m (Const a b) Source #
Instance details
Defined in Data.Functor.Const
Methods
sizeOf :: Const a b -> Int Source #
alignment :: Const a b -> Int Source #
peekElemOff :: Ptr (Const a b) -> Int -> IO (Const a b) Source #
pokeElemOff :: Ptr (Const a b) -> Int -> Const a b -> IO () Source #
peekByteOff :: Ptr b0 -> Int -> IO (Const a b) Source #
pokeByteOff :: Ptr b0 -> Int -> Const a b -> IO () Source #
Instance details
Defined in Data.Functor.Const
Methods
(.&.) :: Const a b -> Const a b -> Const a b Source #
(.|.) :: Const a b -> Const a b -> Const a b Source #
xor :: Const a b -> Const a b -> Const a b Source #
complement :: Const a b -> Const a b Source #
shift :: Const a b -> Int -> Const a b Source #
rotate :: Const a b -> Int -> Const a b Source #
zeroBits :: Const a b Source #
bit :: Int -> Const a b Source #
setBit :: Const a b -> Int -> Const a b Source #
clearBit :: Const a b -> Int -> Const a b Source #
complementBit :: Const a b -> Int -> Const a b Source #
testBit :: Const a b -> Int -> Bool Source #
bitSizeMaybe :: Const a b -> Maybe Int Source #
bitSize :: Const a b -> Int Source #
isSigned :: Const a b -> Bool Source #
shiftL :: Const a b -> Int -> Const a b Source #
unsafeShiftL :: Const a b -> Int -> Const a b Source #
shiftR :: Const a b -> Int -> Const a b Source #
unsafeShiftR :: Const a b -> Int -> Const a b Source #
rotateL :: Const a b -> Int -> Const a b Source #
Instance details
Defined in Data.Functor.Const
Methods
finiteBitSize :: Const a b -> Int Source #
countLeadingZeros :: Const a b -> Int Source #
countTrailingZeros :: Const a b -> Int Source #
Instance details
Defined in Data.Functor.Const
Methods
succ :: Const a b -> Const a b Source #
pred :: Const a b -> Const a b Source #
toEnum :: Int -> Const a b Source #
fromEnum :: Const a b -> Int Source #
enumFrom :: Const a b -> [Const a b] Source #
enumFromThen :: Const a b -> Const a b -> [Const a b] Source #
enumFromTo :: Const a b -> Const a b -> [Const a b] Source #
enumFromThenTo :: Const a b -> Const a b -> Const a b -> [Const a b] Source #
Instance details
Defined in Data.Functor.Const
Methods
exp :: Const a b -> Const a b Source #
log :: Const a b -> Const a b Source #
sqrt :: Const a b -> Const a b Source #
(**) :: Const a b -> Const a b -> Const a b Source #
logBase :: Const a b -> Const a b -> Const a b Source #
sin :: Const a b -> Const a b Source #
cos :: Const a b -> Const a b Source #
tan :: Const a b -> Const a b Source #
asin :: Const a b -> Const a b Source #
acos :: Const a b -> Const a b Source #
atan :: Const a b -> Const a b Source #
sinh :: Const a b -> Const a b Source #
cosh :: Const a b -> Const a b Source #
tanh :: Const a b -> Const a b Source #
asinh :: Const a b -> Const a b Source #
acosh :: Const a b -> Const a b Source #
atanh :: Const a b -> Const a b Source #
log1p :: Const a b -> Const a b Source #
expm1 :: Const a b -> Const a b Source #
Instance details
Defined in Data.Functor.Const
Methods
floatRadix :: Const a b -> Integer Source #
floatDigits :: Const a b -> Int Source #
floatRange :: Const a b -> (Int, Int) Source #
decodeFloat :: Const a b -> (Integer, Int) Source #
encodeFloat :: Integer -> Int -> Const a b Source #
exponent :: Const a b -> Int Source #
significand :: Const a b -> Const a b Source #
scaleFloat :: Int -> Const a b -> Const a b Source #
isNaN :: Const a b -> Bool Source #
isInfinite :: Const a b -> Bool Source #
isDenormalized :: Const a b -> Bool Source #
isNegativeZero :: Const a b -> Bool Source #
Instance details
Defined in Data.Functor.Const
Methods
range :: (Const a b, Const a b) -> [Const a b] Source #
index :: (Const a b, Const a b) -> Const a b -> Int Source #
unsafeIndex :: (Const a b, Const a b) -> Const a b -> Int Source #
inRange :: (Const a b, Const a b) -> Const a b -> Bool Source #
Instance details
Defined in Data.Functor.Const
Methods
(+) :: Const a b -> Const a b -> Const a b Source #
(-) :: Const a b -> Const a b -> Const a b Source #
(*) :: Const a b -> Const a b -> Const a b Source #
negate :: Const a b -> Const a b Source #
abs :: Const a b -> Const a b Source #
signum :: Const a b -> Const a b Source #
fromInteger :: Integer -> Const a b Source #
This instance would be equivalent to the derived instances of the
Const
newtype if the getConst
field were removed
Since: base-4.8.0.0
Instance details
Defined in Data.Functor.Const
Methods
quot :: Const a b -> Const a b -> Const a b Source #
rem :: Const a b -> Const a b -> Const a b Source #
div :: Const a b -> Const a b -> Const a b Source #
mod :: Const a b -> Const a b -> Const a b Source #
quotRem :: Const a b -> Const a b -> (Const a b, Const a b) Source #
divMod :: Const a b -> Const a b -> (Const a b, Const a b) Source #
Instance details
Defined in Data.Functor.Const
This instance would be equivalent to the derived instances of the
Const
newtype if the getConst
field were removed
Since: base-4.8.0.0
Instance details
Defined in Data.Functor.Const
Methods
compare :: Const a b -> Const a b -> Ordering Source #
(<) :: Const a b -> Const a b -> Bool Source #
(<=) :: Const a b -> Const a b -> Bool Source #
(>) :: Const a b -> Const a b -> Bool Source #
(>=) :: Const a b -> Const a b -> Bool Source #
Instance details
Defined in Data.Functor.Const
Instance details
Defined in Data.Functor.Const
newtype WrappedMonad m a Source #
Instances
Instances details
Instance details
Defined in Control.Applicative
Associated Types
type Rep1 (WrappedMonad m) :: k -> Type Source #
Methods
from1 :: forall (a :: k). WrappedMonad m a -> Rep1 (WrappedMonad m) a Source #
to1 :: forall (a :: k). Rep1 (WrappedMonad m) a -> WrappedMonad m a Source #
Instance details
Defined in Control.Applicative
Methods
empty :: WrappedMonad m a Source #
(<|>) :: WrappedMonad m a -> WrappedMonad m a -> WrappedMonad m a Source #
some :: WrappedMonad m a -> WrappedMonad m [a] Source #
many :: WrappedMonad m a -> WrappedMonad m [a] Source #
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 #
Instance details
Defined in Control.Applicative
Methods
fmap :: (a -> b) -> WrappedMonad m a -> WrappedMonad m b Source #
(<$) :: a -> WrappedMonad m b -> WrappedMonad m a Source #
Instance details
Defined in Control.Applicative
Methods
(>>=) :: WrappedMonad m a -> (a -> WrappedMonad m b) -> WrappedMonad m b Source #
(>>) :: WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m b Source #
return :: a -> WrappedMonad m a Source #
Instance details
Defined in Data.Data
Methods
gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> WrappedMonad m a -> c (WrappedMonad m a) Source #
gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (WrappedMonad m a) Source #
toConstr :: WrappedMonad m a -> Constr Source #
dataTypeOf :: WrappedMonad m a -> DataType Source #
dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (WrappedMonad m a)) Source #
dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (WrappedMonad m a)) Source #
gmapT :: (forall b. Data b => b -> b) -> WrappedMonad m a -> WrappedMonad m a Source #
gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> WrappedMonad m a -> r Source #
gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> WrappedMonad m a -> r Source #
gmapQ :: (forall d. Data d => d -> u) -> WrappedMonad m a -> [u] Source #
gmapQi :: Int -> (forall d. Data d => d -> u) -> WrappedMonad m a -> u Source #
gmapM :: Monad m0 => (forall d. Data d => d -> m0 d) -> WrappedMonad m a -> m0 (WrappedMonad m a) Source #
gmapMp :: MonadPlus m0 => (forall d. Data d => d -> m0 d) -> WrappedMonad m a -> m0 (WrappedMonad m a) Source #
gmapMo :: MonadPlus m0 => (forall d. Data d => d -> m0 d) -> WrappedMonad m a -> m0 (WrappedMonad m a) Source #
Instance details
Defined in Control.Applicative
Methods
from :: WrappedMonad m a -> Rep (WrappedMonad m a) x Source #
to :: Rep (WrappedMonad m a) x -> WrappedMonad m a Source #
Instance details
Defined in Control.Applicative
Instance details
Defined in Control.Applicative
newtype WrappedArrow a b c Source #
Instances
Instances details
Instance details
Defined in Control.Applicative
Associated Types
type Rep1 (WrappedArrow a b) :: k -> Type Source #
Methods
from1 :: forall (a0 :: k). WrappedArrow a b a0 -> Rep1 (WrappedArrow a b) a0 Source #
to1 :: forall (a0 :: k). Rep1 (WrappedArrow a b) a0 -> WrappedArrow a b a0 Source #
Instance details
Defined in Control.Applicative
Methods
empty :: WrappedArrow a b a0 Source #
(<|>) :: WrappedArrow a b a0 -> WrappedArrow a b a0 -> WrappedArrow a b a0 Source #
some :: WrappedArrow a b a0 -> WrappedArrow a b [a0] Source #
many :: WrappedArrow a b a0 -> WrappedArrow a b [a0] Source #
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 #
Instance details
Defined in Control.Applicative
Methods
fmap :: (a0 -> b0) -> WrappedArrow a b a0 -> WrappedArrow a b b0 Source #
(<$) :: a0 -> WrappedArrow a b b0 -> WrappedArrow a b a0 Source #
Since: base-4.14.0.0
Instance details
Defined in Data.Data
Methods
gfoldl :: (forall d b0. Data d => c0 (d -> b0) -> d -> c0 b0) -> (forall g. g -> c0 g) -> WrappedArrow a b c -> c0 (WrappedArrow a b c) Source #
gunfold :: (forall b0 r. Data b0 => c0 (b0 -> r) -> c0 r) -> (forall r. r -> c0 r) -> Constr -> c0 (WrappedArrow a b c) Source #
toConstr :: WrappedArrow a b c -> Constr Source #
dataTypeOf :: WrappedArrow a b c -> DataType Source #
dataCast1 :: Typeable t => (forall d. Data d => c0 (t d)) -> Maybe (c0 (WrappedArrow a b c)) Source #
dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c0 (t d e)) -> Maybe (c0 (WrappedArrow a b c)) Source #
gmapT :: (forall b0. Data b0 => b0 -> b0) -> WrappedArrow a b c -> WrappedArrow a b c Source #
gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> WrappedArrow a b c -> r Source #
gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> WrappedArrow a b c -> r Source #
gmapQ :: (forall d. Data d => d -> u) -> WrappedArrow a b c -> [u] Source #
gmapQi :: Int -> (forall d. Data d => d -> u) -> WrappedArrow a b c -> u Source #
gmapM :: Monad m => (forall d. Data d => d -> m d) -> WrappedArrow a b c -> m (WrappedArrow a b c) Source #
gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> WrappedArrow a b c -> m (WrappedArrow a b c) Source #
gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> WrappedArrow a b c -> m (WrappedArrow a b c) Source #
Instance details
Defined in Control.Applicative
Methods
from :: WrappedArrow a b c -> Rep (WrappedArrow a b c) x Source #
to :: Rep (WrappedArrow a b c) x -> WrappedArrow a b c Source #
Instance details
Defined in Control.Applicative
Instance details
Defined in Control.Applicative
Lists, but with an Applicative
functor based on zipping.
Instances
Instances details
Instance details
Defined in Control.Applicative
Methods
fold :: Monoid m => ZipList m -> m Source #
foldMap :: Monoid m => (a -> m) -> ZipList a -> m Source #
foldMap' :: Monoid m => (a -> m) -> ZipList a -> m Source #
foldr :: (a -> b -> b) -> b -> ZipList a -> b Source #
foldr' :: (a -> b -> b) -> b -> ZipList a -> b Source #
foldl :: (b -> a -> b) -> b -> ZipList a -> b Source #
foldl' :: (b -> a -> b) -> b -> ZipList a -> b Source #
foldr1 :: (a -> a -> a) -> ZipList a -> a Source #
foldl1 :: (a -> a -> a) -> ZipList a -> a Source #
toList :: ZipList a -> [a] Source #
null :: ZipList a -> Bool Source #
length :: ZipList a -> Int Source #
elem :: Eq a => a -> ZipList a -> Bool Source #
maximum :: Ord a => ZipList a -> a Source #
minimum :: Ord a => ZipList a -> a Source #
Instance details
Defined in Data.Traversable
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
Instance details
Defined in Data.Data
Methods
gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> ZipList a -> c (ZipList a) Source #
gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (ZipList a) Source #
toConstr :: ZipList a -> Constr Source #
dataTypeOf :: ZipList a -> DataType Source #
dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (ZipList a)) Source #
dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (ZipList a)) Source #
gmapT :: (forall b. Data b => b -> b) -> ZipList a -> ZipList a Source #
gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> ZipList a -> r Source #
gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> ZipList a -> r Source #
gmapQ :: (forall d. Data d => d -> u) -> ZipList a -> [u] Source #
gmapQi :: Int -> (forall d. Data d => d -> u) -> ZipList a -> u Source #
gmapM :: Monad m => (forall d. Data d => d -> m d) -> ZipList a -> m (ZipList a) Source #
gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> ZipList a -> m (ZipList a) Source #
gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> ZipList a -> m (ZipList a) Source #
Instance details
Defined in Control.Applicative
Methods
compare :: ZipList a -> ZipList a -> Ordering Source #
(<) :: ZipList a -> ZipList a -> Bool Source #
(<=) :: ZipList a -> ZipList a -> Bool Source #
(>) :: ZipList a -> ZipList a -> Bool Source #
(>=) :: ZipList a -> ZipList a -> Bool Source #
Instance details
Defined in Control.Applicative
Instance details
Defined in Control.Applicative
Utility functions
(<$>) :: 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, <$>
is function
application lifted over a Functor
.
Examples
Expand
Convert from a
to a Maybe
Int
using Maybe
String
show
:
>>>
show <$> Nothing
Nothing>>>
show <$> Just 3
Just "3"
Convert from an
to an
Either
Int
Int
Either
Int
String
using show
:
>>>
show <$> 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)
(<**>) :: Applicative f => f a -> f (a -> b) -> f b infixl 4 Source #
A variant of <*>
with the arguments reversed.
liftA :: Applicative f => (a -> b) -> f a -> f b Source #
Lift a function to actions.
Equivalent to Functor's fmap
but implemented using only Applicative
's methods:
liftA
f a = pure
f <*>
a
As such this function may be used to implement a Functor
instance from an Applicative
one.
Examples
Expand
Using the Applicative instance for Lists:
>>>
liftA (+1) [1, 2]
[2,3]
Or the Applicative instance for Maybe
>>>
liftA (+1) (Just 3)
Just 4
liftA3 :: Applicative f => (a -> b -> c -> d) -> f a -> f b -> f c -> f d Source #
Lift a ternary function to actions.
optional :: Alternative f => f a -> f (Maybe a) Source #
One or none.
It is useful for modelling any computation that is allowed to fail.
Examples
Expand
Using the Alternative
instance of Control.Monad.Except, the following functions:
>>>
import Control.Monad.Except
>>>
canFail = throwError "it failed" :: Except String Int
>>>
final = return 42 :: Except String Int
Can be combined by allowing the first function to fail:
>>>
runExcept $ canFail *> final
Left "it failed">>>
runExcept $ optional canFail *> final
Right 42
asum :: (Foldable t, Alternative f) => t (f a) -> f a Source #
The sum of a collection of actions using (<|>)
, generalizing concat
.
asum
is just like msum
, but generalised to Alternative
.
Examples
Expand
Basic usage:
>>>
asum [Just "Hello", Nothing, Just "World"]
Just "Hello"