concatMap package:base

concatMap :: Foldable t => (a -> [b]) -> t a -> [b]

Map a function over all the elements of a container and concatenate the resulting lists.

Basic usage:

>>> concatMap (take 3) [[1..], [10..], [100..], [1000..]]
[1,2,3,10,11,12,100,101,102,1000,1001,1002]

>>> concatMap (take 3) (Just [1..])
[1,2,3]

concatMap :: (a -> [b]) -> [a] -> [b]

Map a function returning a list over a list and concatenate the results. concatMap can be seen as the composition of concat and map.

concatMap f xs == (concat . map f) xs

>>> concatMap (\i -> [-i,i]) []
[]

>>> concatMap (\i -> [-i, i]) [1, 2, 3]
[-1,1,-2,2,-3,3]

>>> concatMap ('replicate' 3) [0, 2, 4]
[0,0,0,2,2,2,4,4,4]

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

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]