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Within LTS Haskell 24.27 (ghc-9.10.3)
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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"])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])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"])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.mapExceptionContext :: (ExceptionContext -> ExceptionContext) -> SomeException -> SomeExceptionghc-internal GHC.Internal.Exception.Type No documentation available.
mapAccumL :: (acc -> x -> (acc, y)) -> acc -> Infinite x -> Infinite yinfinite-list Data.List.Infinite Fold an infinite list from the left and return a list of successive reductions, keeping accumulator in a state:
mapAccumL f acc0 (x1 :< x2 :< ...) = let (acc1, y1) = f acc0 x1 in let (acc2, y2) = f acc1 x2 in ... y1 :< y2 :< ...
If you are looking how to traverse with a state, look no further.mapAccumL' :: (acc -> x -> (acc, y)) -> acc -> Infinite x -> Infinite yinfinite-list Data.List.Infinite Same as mapAccumL, but strict in accumulator.
mapEither :: (a -> Either b c) -> Infinite a -> (Infinite b, Infinite c)infinite-list Data.List.Infinite Apply a function to every element of an infinite list and separate Left and Right results. This function isn't productive (e. g., head . fst . mapEither f won't terminate), if no elements of the input list result in Left or Right.
mapMaybe :: (a -> Maybe b) -> Infinite a -> Infinite binfinite-list Data.List.Infinite Apply a function to every element of an infinite list and collect Just results. This function isn't productive (e. g., head . mapMaybe f won't terminate), if no elements of the input list result in Just.
mapped :: forall (f :: Type -> Type) a a' . Functor f => Setter (f a) (f a') a a'lens-family Lens.Family2.Stock An SEC referencing the parameter of a functor.