map package:aeson -package:base

An isomorphism holds when lifted into a functor. For example, if a list contains a bunch of a's which are each isomorphic to a b, the whole list of a's is isomorphic to a list of b's.

>>> ["1","2","3"] ^. mapping _Show :: [Int]
[1,2,3]

>>> ([1,2,3] :: [Int]) ^. from (mapping _Show)
["1","2","3"]

This also hold across different functors:

>>> let l = mapping @[] @Maybe _Show

>>> :t l
l :: (Read b, Show b) => Iso [String] (Maybe String) [b] (Maybe b)

>>> ["1","2","3"] & l %~ Just . sum
Just "6"

mapArray :: (MArray a e' m, MArray a e m, Ix i) => (e' -> e) -> a i e' -> m (a i e)

array Data.Array.Base Data.Array.MArray Data.Array.MArray.Safe

Constructs a new array derived from the original array by applying a function to each of the elements.

mapIndices :: (MArray a e m, Ix i, Ix j) => (i, i) -> (i -> j) -> a j e -> m (a i e)

array Data.Array.Base Data.Array.MArray Data.Array.MArray.Safe

Constructs a new array derived from the original array by applying a function to each of the indices.

mapMArrayM_ :: (MArray a e m, Ix i) => (e -> m b) -> a i e -> m ()

array Data.Array.Base Data.Array.MArray Data.Array.MArray.Safe

Map elements to monadic actions, sequence them left-to-right, and discard the results.

mapConcurrently :: Traversable t => (a -> IO b) -> t a -> IO (t b)

async Control.Concurrent.Async Control.Concurrent.Async.Internal

Maps an IO-performing function over any Traversable data type, performing all the IO actions concurrently, and returning the original data structure with the arguments replaced by the results. If any of the actions throw an exception, then all other actions are cancelled and the exception is re-thrown. For example, mapConcurrently works with lists:

pages <- mapConcurrently getURL ["url1", "url2", "url3"]

If you just have a list of actions, run them concurrently with

results <- mapConcurrently id [act1, act2, act3]

NOTE: mapConcurrently will immediately spawn a thread for each element of the Traversable, so running this on large inputs can lead to resource exhaustion (of memory, file descriptors, or other limited resources). To avoid unbounded resource usage, see Control.Concurrent.Stream.

mapConcurrently_ :: Foldable f => (a -> IO b) -> f a -> IO ()

async Control.Concurrent.Async Control.Concurrent.Async.Internal

mapConcurrently_ is mapConcurrently with the return value discarded; a concurrent equivalent of mapM_.

mapConcurrentlyBounded :: Int -> (a -> IO b) -> [a] -> IO [b]

async Control.Concurrent.Stream

Concurrent map over a list of values, using a bounded number of threads.

data Mapping

amazonka Amazonka.EC2.Metadata

Metadata keys for block-device-mapping/*.

module Data.Aeson.KeyMap

aeson

An abstract interface for maps from JSON keys to values.