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foldlUnliftedArray' :: PrimUnlifted a => (b -> a -> b) -> b -> UnliftedArray a -> bprimitive-unlifted Data.Primitive.Unlifted.Array.ST Strict left-associated fold over the elements of an UnliftedArray.
foldlUnliftedArrayM' :: (PrimUnlifted a, Monad m) => (b -> a -> m b) -> b -> UnliftedArray a -> m bprimitive-unlifted Data.Primitive.Unlifted.Array.ST Strict effectful left-associated fold over the elements of an UnliftedArray.
foldlSmallUnliftedArray :: PrimUnlifted a => (b -> a -> b) -> b -> SmallUnliftedArray a -> bprimitive-unlifted Data.Primitive.Unlifted.SmallArray Lazy left-associated fold over the elements of an SmallUnliftedArray.
foldlSmallUnliftedArray' :: PrimUnlifted a => (b -> a -> b) -> b -> SmallUnliftedArray a -> bprimitive-unlifted Data.Primitive.Unlifted.SmallArray Strict left-associated fold over the elements of an SmallUnliftedArray.
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primitive-unlifted Data.Primitive.Unlifted.SmallArray Strict effectful left-associated fold over the elements of an SmallUnliftedArray.
foldlSmallUnliftedArray :: PrimUnlifted a => (b -> a -> b) -> b -> SmallUnliftedArray a -> bprimitive-unlifted Data.Primitive.Unlifted.SmallArray.ST Lazy left-associated fold over the elements of an SmallUnliftedArray.
foldlSmallUnliftedArray' :: PrimUnlifted a => (b -> a -> b) -> b -> SmallUnliftedArray a -> bprimitive-unlifted Data.Primitive.Unlifted.SmallArray.ST Strict left-associated fold over the elements of an SmallUnliftedArray.
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primitive-unlifted Data.Primitive.Unlifted.SmallArray.ST Strict effectful left-associated fold over the elements of an SmallUnliftedArray.
foldl' :: Foldable t => (b -> a -> b) -> b -> t a -> bprotolude Protolude Left-associative fold of a structure but with strict application of the operator. This ensures that each step of the fold is forced to Weak Head Normal Form before being applied, avoiding the collection of thunks that would otherwise occur. This is often what you want to strictly reduce a finite structure to a single strict result (e.g. sum). For a general Foldable structure this should be semantically identical to,
foldl' f z = foldl' f z . toList
foldlM :: (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m bprotolude Protolude Left-to-right monadic fold over the elements of a structure. Given a structure t with elements (a, b, ..., w, x, y), the result of a fold with an operator function f is equivalent to:
foldlM f z t = do aa <- f z a bb <- f aa b ... xx <- f ww x yy <- f xx y return yy -- Just @return z@ when the structure is empty
For a Monad m, given two functions f1 :: a -> m b and f2 :: b -> m c, their Kleisli composition (f1 >=> f2) :: a -> m c is defined by:(f1 >=> f2) a = f1 a >>= f2
Another way of thinking about foldlM is that it amounts to an application to z of a Kleisli composition:foldlM f z t = flip f a >=> flip f b >=> ... >=> flip f x >=> flip f y $ z
The monadic effects of foldlM are sequenced from left to right. If at some step the bind operator (>>=) short-circuits (as with, e.g., mzero in a MonadPlus), the evaluated effects will be from an initial segment of the element sequence. If you want to evaluate the monadic effects in right-to-left order, or perhaps be able to short-circuit after processing a tail of the sequence of elements, you'll need to use foldrM instead. If the monadic effects don't short-circuit, the outermost application of f is to the rightmost element y, so that, ignoring effects, the result looks like a left fold:((((z `f` a) `f` b) ... `f` w) `f` x) `f` y
Examples
Basic usage:>>> let f a e = do { print e ; return $ e : a } >>> foldlM f [] [0..3] 0 1 2 3 [3,2,1,0]