map package:amazonka-core

map f xs is the list obtained by applying f to each element of xs, i.e.,
map f [x1, x2, ..., xn] == [f x1, f x2, ..., f xn]
map f [x1, x2, ...] == [f x1, f x2, ...]
>>> map (+1) [1, 2, 3]
This can be used to lift any Iso into an arbitrary Functor.
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.
Map each element of a structure to a monadic action, evaluate these actions from left to right, and collect the results. For a version that ignores the results see mapM_.
Map each element of a structure to a monadic action, evaluate these actions from left to right, and ignore the results. For a version that doesn't ignore the results see mapM. As of base 4.8.0.0, mapM_ is just traverse_, specialized to Monad.
The mapMaybe function is a version of map which can throw out elements. In particular, the functional argument returns something of type Maybe b. If this is Nothing, no element is added on to the result list. If it is Just b, then b is included in the result list.

Examples

Using mapMaybe f x is a shortcut for catMaybes $ map f x in most cases:
>>> import Text.Read ( readMaybe )

>>> let readMaybeInt = readMaybe :: String -> Maybe Int

>>> mapMaybe readMaybeInt ["1", "Foo", "3"]
[1,3]

>>> catMaybes $ map readMaybeInt ["1", "Foo", "3"]
[1,3]
If we map the Just constructor, the entire list should be returned:
>>> mapMaybe Just [1,2,3]
[1,2,3]
An associative operation NOTE: This method is redundant and has the default implementation mappend = (<>) since base-4.11.0.0. Should it be implemented manually, since mappend is a synonym for (<>), it is expected that the two functions are defined the same way. In a future GHC release mappend will be removed from Monoid.
A map from keys to values. A map cannot contain duplicate keys; each key can map to at most one value.
Given a means of mapping the elements of a structure to lists, computes the concatenation of all such lists in order.
Combines the elements of a structure, given ways of mapping them to a common monoid.
bifoldMap f g
≡ bifoldr (mappend . f) (mappend . g) mempty
A default definition of bifoldMap in terms of the Bitraversable operations.
bifoldMapDefault f g ≡
getConst . bitraverse (Const . f) (Const . g)
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
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.
The bimapAccumR function behaves like a combination of bimap and bifoldl; 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.
A default definition of bimap in terms of the Bitraversable operations.
bimapDefault f g ≡
runIdentity . bitraverse (Identity . f) (Identity . g)
Alias for bitraverse.
Alias for bitraverse_.
Map a function over all the elements of a container and concatenate the resulting lists.
Using ApplicativeDo: 'fmap f as' can be understood as the do expression
do a <- as
pure (f a)
with an inferred Functor constraint.
Map each element of the structure to a monoid, and combine the results.