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  1. mapAccumR :: Traversable t => (s -> a -> (s, b)) -> s -> t a -> (s, t b)

    ghc-internal GHC.Internal.Data.List

    The mapAccumR function behaves like a combination of fmap and foldr; it applies a function to each element of a structure, passing an accumulating parameter from right to left, and returning a final value of this accumulator together with the new structure.

    Examples

    Basic usage: 
    >>> mapAccumR (\a b -> (a + b, a)) 0 [1..10]
(55,[54,52,49,45,40,34,27,19,10,0])

    >>> mapAccumR (\a b -> (a <> show b, a)) "0" [1..5]
("054321",["05432","0543","054","05","0"])

  2. mapMaybe :: (a -> Maybe b) -> [a] -> [b]

    ghc-internal GHC.Internal.Data.Maybe

    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 GHC.Internal.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]

  3. mappend :: Monoid a => a -> a -> a

    ghc-internal GHC.Internal.Data.Monoid

    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.

  4. mapAccumL :: (acc -> x -> (acc, y)) -> acc -> [x] -> (acc, [y])

    ghc-internal GHC.Internal.Data.OldList

    The mapAccumL function behaves like a combination of map and foldl; it applies a function to each element of a list, passing an accumulating parameter from left to right, and returning a final value of this accumulator together with the new list. mapAccumL does not force accumulator if it is unused: 

    >>> take 1 (snd (mapAccumL (\_ x -> (undefined, x)) undefined ('a' : undefined)))
"a"

  5. mapAccumR :: (acc -> x -> (acc, y)) -> acc -> [x] -> (acc, [y])

    ghc-internal GHC.Internal.Data.OldList

    The mapAccumR function behaves like a combination of map and foldr; it applies a function to each element of a list, passing an accumulating parameter from right to left, and returning a final value of this accumulator together with the new list.

  6. mapAccumL :: Traversable t => (s -> a -> (s, b)) -> s -> t a -> (s, t b)

    ghc-internal GHC.Internal.Data.Traversable

    The mapAccumL function behaves like a combination of fmap and foldl; it applies a function to each element of a structure, passing an accumulating parameter from left to right, and returning a final value of this accumulator together with the new structure.

    Examples

    Basic usage: 
    >>> mapAccumL (\a b -> (a + b, a)) 0 [1..10]
(55,[0,1,3,6,10,15,21,28,36,45])

    >>> mapAccumL (\a b -> (a <> show b, a)) "0" [1..5]
("012345",["0","01","012","0123","01234"])

  7. mapAccumM :: (Monad m, Traversable t) => (s -> a -> m (s, b)) -> s -> t a -> m (s, t b)

    ghc-internal GHC.Internal.Data.Traversable

    The mapAccumM function behaves like a combination of mapM and mapAccumL that traverses the structure while evaluating the actions and passing an accumulating parameter from left to right. It returns a final value of this accumulator together with the new structure. The accumulator is often used for caching the intermediate results of a computation.

    Examples

    Basic usage: 
    >>> let expensiveDouble a = putStrLn ("Doubling " <> show a) >> pure (2 * a)

>>> :{
mapAccumM (\cache a -> case lookup a cache of
Nothing -> expensiveDouble a >>= \double -> pure ((a, double):cache, double)
Just double -> pure (cache, double)
) [] [1, 2, 3, 1, 2, 3]
:}
Doubling 1
Doubling 2
Doubling 3
([(3,6),(2,4),(1,2)],[2,4,6,2,4,6])

  8. mapAccumR :: Traversable t => (s -> a -> (s, b)) -> s -> t a -> (s, t b)

    ghc-internal GHC.Internal.Data.Traversable

    The mapAccumR function behaves like a combination of fmap and foldr; it applies a function to each element of a structure, passing an accumulating parameter from right to left, and returning a final value of this accumulator together with the new structure.

    Examples

    Basic usage: 
    >>> mapAccumR (\a b -> (a + b, a)) 0 [1..10]
(55,[54,52,49,45,40,34,27,19,10,0])

    >>> mapAccumR (\a b -> (a <> show b, a)) "0" [1..5]
("054321",["05432","0543","054","05","0"])

  9. mapM :: (Traversable t, Monad m) => (a -> m b) -> t a -> m (t b)

    ghc-internal GHC.Internal.Data.Traversable

    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_.

    Examples

    mapM is literally a traverse with a type signature restricted to Monad. Its implementation may be more efficient due to additional power of Monad.

  10. mapExceptionContext :: (ExceptionContext -> ExceptionContext) -> SomeException -> SomeException

    ghc-internal GHC.Internal.Exception.Type

    No documentation available.

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