Copyright | (C) 2011-2015 Edward Kmett |
---|---|
License | BSD-style (see the file LICENSE) |
Maintainer | Edward Kmett <ekmett@gmail.com> |
Stability | provisional |
Portability | portable |
Safe Haskell | Trustworthy |
Language | Haskell2010 |
Synopsis
- class Functor (f :: Type -> Type ) where
- (<$>) :: Functor f => (a -> b) -> f a -> f b
- ($>) :: Functor f => f a -> b -> f b
- class Functor f => Apply f where
- (<..>) :: Apply w => w a -> w (a -> b) -> w b
- liftF3 :: Apply w => (a -> b -> c -> d) -> w a -> w b -> w c -> w d
-
newtype
WrappedApplicative
f a =
WrapApplicative
{
- unwrapApplicative :: f a
-
newtype
MaybeApply
f a =
MaybeApply
{
- runMaybeApply :: Either (f a) a
- (<.*>) :: Apply f => f (a -> b) -> MaybeApply f a -> f b
- (<*.>) :: Apply f => MaybeApply f (a -> b) -> f a -> f b
Functors
class Functor (f :: Type -> Type ) where Source #
A type
f
is a Functor if it provides a function
fmap
which, given any types
a
and
b
lets you apply any function from
(a -> b)
to turn an
f a
into an
f b
, preserving the
structure of
f
. Furthermore
f
needs to adhere to the following:
Note, that the second law follows from the free theorem of the type
fmap
and
the first law, so you need only check that the former condition holds.
fmap :: (a -> b) -> f a -> f b Source #
Using
ApplicativeDo
: '
' can be understood as
the
fmap
f as
do
expression
do a <- as pure (f a)
with an inferred
Functor
constraint.
Instances
Functor [] |
Since: base-2.1 |
Functor Maybe |
Since: base-2.1 |
Functor IO |
Since: base-2.1 |
Functor Par1 |
Since: base-4.9.0.0 |
Functor Q | |
Functor Complex |
Since: base-4.9.0.0 |
Functor Min |
Since: base-4.9.0.0 |
Functor Max |
Since: base-4.9.0.0 |
Functor First |
Since: base-4.9.0.0 |
Functor Last |
Since: base-4.9.0.0 |
Functor Option |
Since: base-4.9.0.0 |
Functor ZipList |
Since: base-2.1 |
Functor Identity |
Since: base-4.8.0.0 |
Functor Handler |
Since: base-4.6.0.0 |
Functor STM |
Since: base-4.3.0.0 |
Functor First |
Since: base-4.8.0.0 |
Functor Last |
Since: base-4.8.0.0 |
Functor Dual |
Since: base-4.8.0.0 |
Functor Sum |
Since: base-4.8.0.0 |
Functor Product |
Since: base-4.8.0.0 |
Functor Down |
Since: base-4.11.0.0 |
Functor ReadP |
Since: base-2.1 |
Functor NonEmpty |
Since: base-4.9.0.0 |
Functor IntMap | |
Functor Tree | |
Functor Seq | |
Functor FingerTree | |
Defined in Data.Sequence.Internal fmap :: (a -> b) -> FingerTree a -> FingerTree b Source # (<$) :: a -> FingerTree b -> FingerTree a Source # |
|
Functor Digit | |
Functor Node | |
Functor Elem | |
Functor ViewL | |
Functor ViewR | |
Functor Doc | |
Functor AnnotDetails | |
Defined in Text.PrettyPrint.Annotated.HughesPJ fmap :: (a -> b) -> AnnotDetails a -> AnnotDetails b Source # (<$) :: a -> AnnotDetails b -> AnnotDetails a Source # |
|
Functor Span | |
Functor P |
Since: base-4.8.0.0 |
Functor ( Either a) |
Since: base-3.0 |
Functor ( V1 :: Type -> Type ) |
Since: base-4.9.0.0 |
Functor ( U1 :: Type -> Type ) |
Since: base-4.9.0.0 |
Functor ( (,) a) |
Since: base-2.1 |
Functor ( Array i) |
Since: base-2.1 |
Functor ( Arg a) |
Since: base-4.9.0.0 |
Monad m => Functor ( WrappedMonad m) |
Since: base-2.1 |
Defined in Control.Applicative fmap :: (a -> b) -> WrappedMonad m a -> WrappedMonad m b Source # (<$) :: a -> WrappedMonad m b -> WrappedMonad m a Source # |
|
Arrow a => Functor ( ArrowMonad a) |
Since: base-4.6.0.0 |
Defined in Control.Arrow fmap :: (a0 -> b) -> ArrowMonad a a0 -> ArrowMonad a b Source # (<$) :: a0 -> ArrowMonad a b -> ArrowMonad a a0 Source # |
|
Functor ( Proxy :: Type -> Type ) |
Since: base-4.7.0.0 |
Functor ( Map k) | |
Functor f => Functor ( Lift f) | |
Functor m => Functor ( MaybeT m) | |
Functor m => Functor ( ListT m) | |
Functor ( HashMap k) | |
Functor f => Functor ( MaybeApply f) Source # | |
Defined in Data.Functor.Bind.Class fmap :: (a -> b) -> MaybeApply f a -> MaybeApply f b Source # (<$) :: a -> MaybeApply f b -> MaybeApply f a Source # |
|
Functor f => Functor ( WrappedApplicative f) Source # | |
Defined in Data.Functor.Bind.Class fmap :: (a -> b) -> WrappedApplicative f a -> WrappedApplicative f b Source # (<$) :: a -> WrappedApplicative f b -> WrappedApplicative f a Source # |
|
Functor f => Functor ( Rec1 f) |
Since: base-4.9.0.0 |
Functor ( URec Char :: Type -> Type ) |
Since: base-4.9.0.0 |
Functor ( URec Double :: Type -> Type ) |
Since: base-4.9.0.0 |
Functor ( URec Float :: Type -> Type ) |
Since: base-4.9.0.0 |
Functor ( URec Int :: Type -> Type ) |
Since: base-4.9.0.0 |
Functor ( URec Word :: Type -> Type ) |
Since: base-4.9.0.0 |
Functor ( URec ( Ptr ()) :: Type -> Type ) |
Since: base-4.9.0.0 |
Functor ( (,,) a b) |
Since: base-4.14.0.0 |
Arrow a => Functor ( WrappedArrow a b) |
Since: base-2.1 |
Defined in Control.Applicative fmap :: (a0 -> b0) -> WrappedArrow a b a0 -> WrappedArrow a b b0 Source # (<$) :: a0 -> WrappedArrow a b b0 -> WrappedArrow a b a0 Source # |
|
Functor m => Functor ( Kleisli m a) |
Since: base-4.14.0.0 |
Functor ( Const m :: Type -> Type ) |
Since: base-2.1 |
Functor f => Functor ( Ap f) |
Since: base-4.12.0.0 |
Functor f => Functor ( Alt f) |
Since: base-4.8.0.0 |
Bifunctor p => Functor ( Join p) | |
Functor w => Functor ( TracedT m w) | |
Functor w => Functor ( StoreT s w) | |
Functor w => Functor ( EnvT e w) | |
Functor m => Functor ( IdentityT m) | |
( Applicative f, Monad f) => Functor ( WhenMissing f x) |
Since: containers-0.5.9 |
Defined in Data.IntMap.Internal fmap :: (a -> b) -> WhenMissing f x a -> WhenMissing f x b Source # (<$) :: a -> WhenMissing f x b -> WhenMissing f x a Source # |
|
Functor ( Tagged s) | |
Functor f => Functor ( Reverse f) |
Derived instance. |
Functor ( Constant a :: Type -> Type ) | |
Functor m => Functor ( WriterT w m) | |
Functor m => Functor ( WriterT w m) | |
Functor m => Functor ( WriterT w m) | |
Functor m => Functor ( StateT s m) | |
Functor m => Functor ( StateT s m) | |
Functor m => Functor ( ReaderT r m) | |
Functor m => Functor ( ExceptT e m) | |
Functor m => Functor ( ErrorT e m) | |
Functor f => Functor ( Backwards f) |
Derived instance. |
Functor (Mag a b) | |
Functor f => Functor ( Static f a) Source # | |
Functor ((->) r :: Type -> Type ) |
Since: base-2.1 |
Functor ( K1 i c :: Type -> Type ) |
Since: base-4.9.0.0 |
( Functor f, Functor g) => Functor (f :+: g) |
Since: base-4.9.0.0 |
( Functor f, Functor g) => Functor (f :*: g) |
Since: base-4.9.0.0 |
Functor ( (,,,) a b c) |
Since: base-4.14.0.0 |
( Functor f, Functor g) => Functor ( Product f g) |
Since: base-4.9.0.0 |
( Functor f, Functor g) => Functor ( Sum f g) |
Since: base-4.9.0.0 |
Functor ( Cokleisli w a) | |
Functor f => Functor ( WhenMatched f x y) |
Since: containers-0.5.9 |
Defined in Data.IntMap.Internal fmap :: (a -> b) -> WhenMatched f x y a -> WhenMatched f x y b Source # (<$) :: a -> WhenMatched f x y b -> WhenMatched f x y a Source # |
|
( Applicative f, Monad f) => Functor ( WhenMissing f k x) |
Since: containers-0.5.9 |
Defined in Data.Map.Internal fmap :: (a -> b) -> WhenMissing f k x a -> WhenMissing f k x b Source # (<$) :: a -> WhenMissing f k x b -> WhenMissing f k x a Source # |
|
Functor ( ContT r m) | |
Functor f => Functor ( M1 i c f) |
Since: base-4.9.0.0 |
( Functor f, Functor g) => Functor (f :.: g) |
Since: base-4.9.0.0 |
( Functor f, Functor g) => Functor ( Compose f g) |
Since: base-4.9.0.0 |
Bifunctor p => Functor ( WrappedBifunctor p a) | |
Defined in Data.Bifunctor.Wrapped fmap :: (a0 -> b) -> WrappedBifunctor p a a0 -> WrappedBifunctor p a b Source # (<$) :: a0 -> WrappedBifunctor p a b -> WrappedBifunctor p a a0 Source # |
|
Functor g => Functor ( Joker g a) | |
Bifunctor p => Functor ( Flip p a) | |
Functor ( Clown f a :: Type -> Type ) | |
Functor f => Functor ( WhenMatched f k x y) |
Since: containers-0.5.9 |
Defined in Data.Map.Internal fmap :: (a -> b) -> WhenMatched f k x y a -> WhenMatched f k x y b Source # (<$) :: a -> WhenMatched f k x y b -> WhenMatched f k x y a Source # |
|
Functor m => Functor ( RWST r w s m) | |
Functor m => Functor ( RWST r w s m) | |
Functor m => Functor ( RWST r w s m) | |
( Functor (f a), Functor (g a)) => Functor ( Product f g a) | |
( Functor f, Bifunctor p) => Functor ( Tannen f p a) | |
( Bifunctor p, Functor g) => Functor ( Biff p f g a) | |
(<$>) :: 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,
<$>
is function
application lifted over a
Functor
.
Examples
Convert from a
to a
Maybe
Int
using
Maybe
String
show
:
>>>
show <$> 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 <$> (2,2)
(2,True)
($>) :: Functor f => f a -> b -> f b infixl 4 Source #
Flipped version of
<$
.
Using
ApplicativeDo
: '
as
' can be understood as the
$>
b
do
expression
do as pure b
with an inferred
Functor
constraint.
Examples
Replace the contents of a
with a constant
Maybe
Int
String
:
>>>
Nothing $> "foo"
Nothing>>>
Just 90210 $> "foo"
Just "foo"
Replace the contents of an
with a constant
Either
Int
Int
String
, resulting in an
:
Either
Int
String
>>>
Left 8675309 $> "foo"
Left 8675309>>>
Right 8675309 $> "foo"
Right "foo"
Replace each element of a list with a constant
String
:
>>>
[1,2,3] $> "foo"
["foo","foo","foo"]
Replace the second element of a pair with a constant
String
:
>>>
(1,2) $> "foo"
(1,"foo")
Since: base-4.7.0.0
Apply - a strong lax semimonoidal endofunctor
class Functor f => Apply f where Source #
A strong lax semi-monoidal endofunctor.
This is equivalent to an
Applicative
without
pure
.
Laws:
(.
)<$>
u<.>
v<.>
w = u<.>
(v<.>
w) x<.>
(f<$>
y) = (.
f)<$>
x<.>
y f<$>
(x<.>
y) = (f.
)<$>
x<.>
y
The laws imply that
.>
and
<.
really ignore their
left and right results, respectively, and really
return their right and left results, respectively.
Specifically,
(mf<$>
m).>
(nf<$>
n) = nf<$>
(m.>
n) (mf<$>
m)<.
(nf<$>
n) = mf<$>
(m<.
n)
(<.>) :: f (a -> b) -> f a -> f b infixl 4 Source #
(.>) :: f a -> f b -> f b infixl 4 Source #
(<.) :: f a -> f b -> f a infixl 4 Source #
liftF2 :: (a -> b -> c) -> f a -> f b -> f c Source #
Lift a binary function into a comonad with zipping
Instances
(<..>) :: Apply w => w a -> w (a -> b) -> w b infixl 4 Source #
A variant of
<.>
with the arguments reversed.
liftF3 :: Apply w => (a -> b -> c -> d) -> w a -> w b -> w c -> w d Source #
Lift a ternary function into a comonad with zipping
Wrappers
newtype WrappedApplicative f a Source #
Wrap an
Applicative
to be used as a member of
Apply
WrapApplicative | |
|
Instances
newtype MaybeApply f a Source #
Transform an Apply into an Applicative by adding a unit.
MaybeApply | |
|
Instances
(<.*>) :: Apply f => f (a -> b) -> MaybeApply f a -> f b infixl 4 Source #
Apply a non-empty container of functions to a possibly-empty-with-unit container of values.
(<*.>) :: Apply f => MaybeApply f (a -> b) -> f a -> f b infixl 4 Source #
Apply a possibly-empty-with-unit container of functions to a non-empty container of values.