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Typeclasses

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class Foldable t

Class of data structures that can be folded to a summary value. Methods:

• fold : Monoid m => t m -> m Combine the elements of a structure using a monoid.
• foldMap : Monoid m => (a -> m) -> t a -> m Combine the elements of a structure using a monoid.
• foldr : (a -> b -> b) -> b -> t a -> b Right-associative fold of a structure.
• foldl : (b -> a -> b) -> b -> t a -> b Left-associative fold of a structure.
• foldr1 : (a -> a -> a) -> t a -> a A variant of foldr that has no base case, and thus should only be applied to non-empty structures.
• foldl1 : (a -> a -> a) -> t a -> a A variant of foldl that has no base case, and thus should only be applied to non-empty structures.
• toList : t a -> [a] List of elements of a structure, from left to right.
• null : t a -> Bool Test whether the structure is empty. The default implementation is optimized for structures that are similar to cons-lists, because there is no general way to do better.
• length : t a -> Int Returns the size/length of a finite structure as an Int. The default implementation is optimized for structures that are similar to cons-lists, because there is no general way to do better.
• elem : Eq a => a -> t a -> Bool Does the element occur in the structure?
• sum : Additive a => t a -> a The sum function computes the sum of the numbers of a structure.
• product : Multiplicative a => t a -> a The product function computes the product of the numbers of a structure.
• minimum : Ord a => t a -> a The least element of a non-empty structure.
• maximum : Ord a => t a -> a The largest element of a non-empty structure.

Instances:

• instance Ord k => Foldable (Map k)
• instance Foldable TextMap
• instance Foldable Optional
• instance Foldable NonEmpty
• instance Foldable Set
• instance Foldable (Validation err)
• instance Foldable (Either a)
• instance Foldable []
• instance Foldable a

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Functions

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mapA_

mapA_ : (Foldable t, Applicative f) => (a -> f b) -> t a -> f () Map each element of a structure to an action, evaluate these actions from left to right, and ignore the results. For a version that doesn’t ignore the results see ‘DA.Traversable.mapA’.

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forA_

forA_ : (Foldable t, Applicative f) => t a -> (a -> f b) -> f () ‘for_’ is ‘mapA_’ with its arguments flipped. For a version that doesn’t ignore the results see ‘DA.Traversable.forA’.

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forM_

forM_ : (Foldable t, Applicative f) => t a -> (a -> f b) -> f ()

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sequence_

sequence_ : (Foldable t, Action m) => t (m a) -> m () Evaluate each action in the structure from left to right, and ignore the results. For a version that doesn’t ignore the results see ‘DA.Traversable.sequence’.

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concat

concat : Foldable t => t [a] -> [a] The concatenation of all the elements of a container of lists.

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and

and : Foldable t => t Bool -> Bool and returns the conjunction of a container of Bools. For the result to be True, the container must be finite; False, however, results from a False value finitely far from the left end.

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or

or : Foldable t => t Bool -> Bool or returns the disjunction of a container of Bools. For the result to be False, the container must be finite; True, however, results from a True value finitely far from the left end.

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any

any : Foldable t => (a -> Bool) -> t a -> Bool Determines whether any element of the structure satisfies the predicate.

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all

all : Foldable t => (a -> Bool) -> t a -> Bool Determines whether all elements of the structure satisfy the predicate.