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  1. fmap :: Functor f => (a -> b) -> f a -> f b

    base Control.Monad

    fmap is used to apply a function of type (a -> b) to a value of type f a, where f is a functor, to produce a value of type f b. Note that for any type constructor with more than one parameter (e.g., Either), only the last type parameter can be modified with fmap (e.g., b in `Either a b`). Some type constructors with two parameters or more have a Bifunctor instance that allows both the last and the penultimate parameters to be mapped over.

    Examples

    Convert from a Maybe Int to a Maybe String using show: 
    >>> fmap show Nothing
Nothing

>>> fmap show (Just 3)
Just "3"
    Convert from an Either Int Int to an Either Int String using show: 
    >>> fmap show (Left 17)
Left 17

>>> fmap show (Right 17)
Right "17"
    Double each element of a list: 
    >>> fmap (*2) [1,2,3]
[2,4,6]
    Apply even to the second element of a pair: 
    >>> fmap even (2,2)
(2,True)
    It may seem surprising that the function is only applied to the last element of the tuple compared to the list example above which applies it to every element in the list. To understand, remember that tuples are type constructors with multiple type parameters: a tuple of 3 elements (a,b,c) can also be written (,,) a b c and its Functor instance is defined for Functor ((,,) a b) (i.e., only the third parameter is free to be mapped over with fmap). It explains why fmap can be used with tuples containing values of different types as in the following example: 
    >>> fmap even ("hello", 1.0, 4)
("hello",1.0,True)

  2. fmap :: Functor f => (a -> b) -> f a -> f b

    base Control.Monad.Instances

    fmap is used to apply a function of type (a -> b) to a value of type f a, where f is a functor, to produce a value of type f b. Note that for any type constructor with more than one parameter (e.g., Either), only the last type parameter can be modified with fmap (e.g., b in `Either a b`). Some type constructors with two parameters or more have a Bifunctor instance that allows both the last and the penultimate parameters to be mapped over.

    Examples

    Convert from a Maybe Int to a Maybe String using show: 
    >>> fmap show Nothing
Nothing

>>> fmap show (Just 3)
Just "3"
    Convert from an Either Int Int to an Either Int String using show: 
    >>> fmap show (Left 17)
Left 17

>>> fmap show (Right 17)
Right "17"
    Double each element of a list: 
    >>> fmap (*2) [1,2,3]
[2,4,6]
    Apply even to the second element of a pair: 
    >>> fmap even (2,2)
(2,True)
    It may seem surprising that the function is only applied to the last element of the tuple compared to the list example above which applies it to every element in the list. To understand, remember that tuples are type constructors with multiple type parameters: a tuple of 3 elements (a,b,c) can also be written (,,) a b c and its Functor instance is defined for Functor ((,,) a b) (i.e., only the third parameter is free to be mapped over with fmap). It explains why fmap can be used with tuples containing values of different types as in the following example: 
    >>> fmap even ("hello", 1.0, 4)
("hello",1.0,True)

  3. biconcatMap :: Bifoldable t => (a -> [c]) -> (b -> [c]) -> t a b -> [c]

    base Data.Bifoldable

    Given a means of mapping the elements of a structure to lists, computes the concatenation of all such lists in order.

    Examples

    Basic usage: 
    >>> biconcatMap (take 3) (fmap digitToInt) ([1..], "89")
[1,2,3,8,9]

    >>> biconcatMap (take 3) (fmap digitToInt) (Left [1..])
[1,2,3]

    >>> biconcatMap (take 3) (fmap digitToInt) (Right "89")
[8,9]

  4. bifoldMap :: (Bifoldable p, Monoid m) => (a -> m) -> (b -> m) -> p a b -> m

    base Data.Bifoldable

    Combines the elements of a structure, given ways of mapping them to a common monoid. 

    bifoldMap f g ≡ bifoldr (mappend . f) (mappend . g) mempty

    Examples

    Basic usage: 
    >>> bifoldMap (take 3) (fmap digitToInt) ([1..], "89")
[1,2,3,8,9]

    >>> bifoldMap (take 3) (fmap digitToInt) (Left [1..])
[1,2,3]

    >>> bifoldMap (take 3) (fmap digitToInt) (Right "89")
[8,9]

  5. bimapM_ :: (Bifoldable t, Applicative f) => (a -> f c) -> (b -> f d) -> t a b -> f ()

    base Data.Bifoldable

    Alias for bitraverse_.

  6. bifoldMap1 :: (Bifoldable1 t, Semigroup m) => (a -> m) -> (b -> m) -> t a b -> m

    base Data.Bifoldable1

    No documentation available.

  7. bimap :: Bifunctor p => (a -> b) -> (c -> d) -> p a c -> p b d

    base Data.Bifunctor

    Map over both arguments at the same time. 

    bimap f g ≡ first f . second g

    Examples

    >>> bimap toUpper (+1) ('j', 3)
('J',4)

    >>> bimap toUpper (+1) (Left 'j')
Left 'J'

    >>> bimap toUpper (+1) (Right 3)
Right 4

  8. bifoldMapDefault :: (Bitraversable t, Monoid m) => (a -> m) -> (b -> m) -> t a b -> m

    base Data.Bitraversable

    A default definition of bifoldMap in terms of the Bitraversable operations. 

    bifoldMapDefault f g ≡
getConst . bitraverse (Const . f) (Const . g)

  9. bimapAccumL :: Bitraversable t => (a -> b -> (a, c)) -> (a -> d -> (a, e)) -> a -> t b d -> (a, t c e)

    base Data.Bitraversable

    The bimapAccumL function behaves like a combination of bimap and bifoldl; it traverses a structure from left to right, threading a state of type a and using the given actions to compute new elements for the structure.

    Examples

    Basic usage: 
    >>> bimapAccumL (\acc bool -> (acc + 1, show bool)) (\acc string -> (acc * 2, reverse string)) 3 (True, "foo")
(8,("True","oof"))

  10. bimapAccumR :: Bitraversable t => (a -> b -> (a, c)) -> (a -> d -> (a, e)) -> a -> t b d -> (a, t c e)

    base Data.Bitraversable

    The bimapAccumR function behaves like a combination of bimap and bifoldr; it traverses a structure from right to left, threading a state of type a and using the given actions to compute new elements for the structure.

    Examples

    Basic usage: 
    >>> bimapAccumR (\acc bool -> (acc + 1, show bool)) (\acc string -> (acc * 2, reverse string)) 3 (True, "foo")
(7,("True","oof"))

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