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1. foldlWithKey' :: Enum k => (a -> k -> b -> a) -> a -> EnumMap k b -> a

   enummapset	Data.EnumMap.Strict

   No documentation available.

2. foldl' :: Enum k => (a -> k -> a) -> a -> EnumSet k -> a

   enummapset	Data.EnumSet

   No documentation available.

3. foldl1Elems :: (a -> a -> a) -> Array i a -> a

   ghc-internal	GHC.Internal.Arr

   A left fold over the elements with no starting value

4. foldlElems :: (b -> a -> b) -> b -> Array i a -> b

   ghc-internal	GHC.Internal.Arr

   A left fold over the elements

5. foldlElems' :: (b -> a -> b) -> b -> Array i a -> b

   ghc-internal	GHC.Internal.Arr

   A strict left fold over the elements

6. foldl' :: Foldable t => (b -> a -> b) -> b -> t a -> b

   ghc-internal	GHC.Internal.Data.Foldable

   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
   

7. foldl1 :: Foldable t => (a -> a -> a) -> t a -> a

   ghc-internal	GHC.Internal.Data.Foldable

   A variant of foldl that has no base case, and thus may only be applied to non-empty structures. This function is non-total and will raise a runtime exception if the structure happens to be empty.

   foldl1 f = foldl1 f . toList
   

   Examples

   Basic usage:

   >>> foldl1 (+) [1..4]
   10
   

   >>> foldl1 (+) []
   *** Exception: Prelude.foldl1: empty list
   

   >>> foldl1 (+) Nothing
   *** Exception: foldl1: empty structure
   

   >>> foldl1 (-) [1..4]
   -8
   

   >>> foldl1 (&&) [True, False, True, True]
   False
   

   >>> foldl1 (||) [False, False, True, True]
   True
   

   >>> foldl1 (+) [1..]
   * Hangs forever *
   

8. foldlM :: (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m b

   ghc-internal	GHC.Internal.Data.Foldable

   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]
   

9. foldl' :: Foldable t => (b -> a -> b) -> b -> t a -> b

   ghc-internal	GHC.Internal.Data.List

   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
   

10. foldl1 :: Foldable t => (a -> a -> a) -> t a -> a

    ghc-internal	GHC.Internal.Data.List

    A variant of foldl that has no base case, and thus may only be applied to non-empty structures. This function is non-total and will raise a runtime exception if the structure happens to be empty.

    foldl1 f = foldl1 f . toList
    

    Examples

    Basic usage:

    >>> foldl1 (+) [1..4]
    10
    

    >>> foldl1 (+) []
    *** Exception: Prelude.foldl1: empty list
    

    >>> foldl1 (+) Nothing
    *** Exception: foldl1: empty structure
    

    >>> foldl1 (-) [1..4]
    -8
    

    >>> foldl1 (&&) [True, False, True, True]
    False
    

    >>> foldl1 (||) [False, False, True, True]
    True
    

    >>> foldl1 (+) [1..]
    * Hangs forever *
    

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