Relude.Foldable.Reexport

Reexports Data.Foldable and Data.Traversable.

Foldable reexports

class Foldable (t :: Type -> Type) where

The Foldable class represents data structures that can be reduced to a summary value one element at a time. Strict left-associative folds are a good fit for space-efficient reduction, while lazy right-associative folds are a good fit for corecursive iteration, or for folds that short-circuit after processing an initial subsequence of the structure's elements.

Instances can be derived automatically by enabling the DeriveFoldable extension. For example, a derived instance for a binary tree might be:

{-# LANGUAGE DeriveFoldable #-}
data Tree a = Empty
            | Leaf a
            | Node (Tree a) a (Tree a)
    deriving Foldable

A more detailed description can be found in the Overview section of Data.Foldable.

For the class laws see the Laws section of Data.Foldable.

Minimal complete definition

foldMap | foldr

Methods

fold :: Monoid m => t m -> m

Given a structure with elements whose type is a Monoid, combine them via the monoid's (<>) operator. This fold is right-associative and lazy in the accumulator. When you need a strict left-associative fold, use foldMap' instead, with id as the map.

Examples

Basic usage:

>>> fold [[1, 2, 3], [4, 5], [6], []]
[1,2,3,4,5,6]

>>> fold $ Node (Leaf (Sum 1)) (Sum 3) (Leaf (Sum 5))
Sum {getSum = 9}

Folds of unbounded structures do not terminate when the monoid's (<>) operator is strict:

>>> fold (repeat Nothing)
* Hangs forever *

Lazy corecursive folds of unbounded structures are fine:

>>> take 12 $ fold $ map (\i -> [i..i+2]) [0..]
[0,1,2,1,2,3,2,3,4,3,4,5]
>>> sum $ take 4000000 $ fold $ map (\i -> [i..i+2]) [0..]
2666668666666

foldMap :: Monoid m => (a -> m) -> t a -> m

Map each element of the structure into a monoid, and combine the results with (<>). This fold is right-associative and lazy in the accumulator. For strict left-associative folds consider foldMap' instead.

Examples

Basic usage:

>>> foldMap Sum [1, 3, 5]
Sum {getSum = 9}

>>> foldMap Product [1, 3, 5]
Product {getProduct = 15}

>>> foldMap (replicate 3) [1, 2, 3]
[1,1,1,2,2,2,3,3,3]

When a Monoid's (<>) is lazy in its second argument, foldMap can return a result even from an unbounded structure. For example, lazy accumulation enables Data.ByteString.Builder to efficiently serialise large data structures and produce the output incrementally:

>>> import qualified Data.ByteString.Lazy as L
>>> import qualified Data.ByteString.Builder as B
>>> let bld :: Int -> B.Builder; bld i = B.intDec i <> B.word8 0x20
>>> let lbs = B.toLazyByteString $ foldMap bld [0..]
>>> L.take 64 lbs
"0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24"

foldMap' :: Monoid m => (a -> m) -> t a -> m

A left-associative variant of foldMap that is strict in the accumulator. Use this method for strict reduction when partial results are merged via (<>).

Examples

Define a Monoid over finite bit strings under xor. Use it to strictly compute the xor of a list of Int values.

>>> :set -XGeneralizedNewtypeDeriving
>>> import Data.Bits (Bits, FiniteBits, xor, zeroBits)
>>> import Data.Foldable (foldMap')
>>> import Numeric (showHex)
>>> 
>>> newtype X a = X a deriving (Eq, Bounded, Enum, Bits, FiniteBits)
>>> instance Bits a => Semigroup (X a) where X a <> X b = X (a `xor` b)
>>> instance Bits a => Monoid    (X a) where mempty     = X zeroBits
>>> 
>>> let bits :: [Int]; bits = [0xcafe, 0xfeed, 0xdeaf, 0xbeef, 0x5411]
>>> (\ (X a) -> showString "0x" . showHex a $ "") $ foldMap' X bits
"0x42"

Since: base-4.13.0.0

foldr :: (a -> b -> b) -> b -> t a -> b

Right-associative fold of a structure, lazy in the accumulator.

In the case of lists, foldr, when applied to a binary operator, a starting value (typically the right-identity of the operator), and a list, reduces the list using the binary operator, from right to left:

foldr f z [x1, x2, ..., xn] == x1 `f` (x2 `f` ... (xn `f` z)...)

Note that since the head of the resulting expression is produced by an application of the operator to the first element of the list, given an operator lazy in its right argument, foldr can produce a terminating expression from an unbounded list.

For a general Foldable structure this should be semantically identical to,

foldr f z = foldr f z . toList

Examples

Basic usage:

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

>>> foldr (||) False []
False

>>> foldr (\c acc -> acc ++ [c]) "foo" ['a', 'b', 'c', 'd']
"foodcba"

Infinite structures

⚠️ Applying foldr to infinite structures usually doesn't terminate.

It may still terminate under one of the following conditions:

• the folding function is short-circuiting
• the folding function is lazy on its second argument

Short-circuiting

(||) short-circuits on True values, so the following terminates because there is a True value finitely far from the left side:

>>> foldr (||) False (True : repeat False)
True

But the following doesn't terminate:

>>> foldr (||) False (repeat False ++ [True])
* Hangs forever *

Laziness in the second argument

Applying foldr to infinite structures terminates when the operator is lazy in its second argument (the initial accumulator is never used in this case, and so could be left undefined, but [] is more clear):

>>> take 5 $ foldr (\i acc -> i : fmap (+3) acc) [] (repeat 1)
[1,4,7,10,13]

foldl' :: (b -> a -> b) -> b -> t a -> b

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

Since: base-4.6.0.0

toList :: t a -> [a]

List of elements of a structure, from left to right. If the entire list is intended to be reduced via a fold, just fold the structure directly bypassing the list.

Examples

Basic usage:

>>> toList Nothing
[]

>>> toList (Just 42)
[42]

>>> toList (Left "foo")
[]

>>> toList (Node (Leaf 5) 17 (Node Empty 12 (Leaf 8)))
[5,17,12,8]

For lists, toList is the identity:

>>> toList [1, 2, 3]
[1,2,3]

Since: base-4.8.0.0

null :: t a -> Bool

Test whether the structure is empty. The default implementation is Left-associative and lazy in both the initial element and the accumulator. Thus optimised for structures where the first element can be accessed in constant time. Structures where this is not the case should have a non-default implementation.

Examples

Basic usage:

>>> null []
True

>>> null [1]
False

null is expected to terminate even for infinite structures. The default implementation terminates provided the structure is bounded on the left (there is a leftmost element).

>>> null [1..]
False

Since: base-4.8.0.0

length :: t a -> Int

Returns the size/length of a finite structure as an Int. The default implementation just counts elements starting with the leftmost. Instances for structures that can compute the element count faster than via element-by-element counting, should provide a specialised implementation.

Examples

Basic usage:

>>> length []
0

>>> length ['a', 'b', 'c']
3
>>> length [1..]
* Hangs forever *

Since: base-4.8.0.0

Instances

Foldable ZipList

Since: base-4.9.0.0

Defined in Control.Applicative

Methods

fold :: Monoid m => ZipList m -> m

foldMap :: Monoid m => (a -> m) -> ZipList a -> m

foldMap' :: Monoid m => (a -> m) -> ZipList a -> m

foldr :: (a -> b -> b) -> b -> ZipList a -> b

foldr' :: (a -> b -> b) -> b -> ZipList a -> b

foldl :: (b -> a -> b) -> b -> ZipList a -> b

foldl' :: (b -> a -> b) -> b -> ZipList a -> b

foldr1 :: (a -> a -> a) -> ZipList a -> a

foldl1 :: (a -> a -> a) -> ZipList a -> a

toList :: ZipList a -> [a]

null :: ZipList a -> Bool

length :: ZipList a -> Int

elem :: Eq a => a -> ZipList a -> Bool

maximum :: Ord a => ZipList a -> a

minimum :: Ord a => ZipList a -> a

sum :: Num a => ZipList a -> a

product :: Num a => ZipList a -> a

Foldable Complex

Since: base-4.9.0.0

Defined in Data.Complex

Methods

fold :: Monoid m => Complex m -> m

foldMap :: Monoid m => (a -> m) -> Complex a -> m

foldMap' :: Monoid m => (a -> m) -> Complex a -> m

foldr :: (a -> b -> b) -> b -> Complex a -> b

foldr' :: (a -> b -> b) -> b -> Complex a -> b

foldl :: (b -> a -> b) -> b -> Complex a -> b

foldl' :: (b -> a -> b) -> b -> Complex a -> b

foldr1 :: (a -> a -> a) -> Complex a -> a

foldl1 :: (a -> a -> a) -> Complex a -> a

toList :: Complex a -> [a]

null :: Complex a -> Bool

length :: Complex a -> Int

elem :: Eq a => a -> Complex a -> Bool

maximum :: Ord a => Complex a -> a

minimum :: Ord a => Complex a -> a

sum :: Num a => Complex a -> a

product :: Num a => Complex a -> a

Foldable Identity

Since: base-4.8.0.0

Defined in Data.Functor.Identity

Methods

fold :: Monoid m => Identity m -> m

foldMap :: Monoid m => (a -> m) -> Identity a -> m

foldMap' :: Monoid m => (a -> m) -> Identity a -> m

foldr :: (a -> b -> b) -> b -> Identity a -> b

foldr' :: (a -> b -> b) -> b -> Identity a -> b

foldl :: (b -> a -> b) -> b -> Identity a -> b

foldl' :: (b -> a -> b) -> b -> Identity a -> b

foldr1 :: (a -> a -> a) -> Identity a -> a

foldl1 :: (a -> a -> a) -> Identity a -> a

toList :: Identity a -> [a]

null :: Identity a -> Bool

length :: Identity a -> Int

elem :: Eq a => a -> Identity a -> Bool

maximum :: Ord a => Identity a -> a

minimum :: Ord a => Identity a -> a

sum :: Num a => Identity a -> a

product :: Num a => Identity a -> a

Foldable First

Since: base-4.8.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => First m -> m

foldMap :: Monoid m => (a -> m) -> First a -> m

foldMap' :: Monoid m => (a -> m) -> First a -> m

foldr :: (a -> b -> b) -> b -> First a -> b

foldr' :: (a -> b -> b) -> b -> First a -> b

foldl :: (b -> a -> b) -> b -> First a -> b

foldl' :: (b -> a -> b) -> b -> First a -> b

foldr1 :: (a -> a -> a) -> First a -> a

foldl1 :: (a -> a -> a) -> First a -> a

toList :: First a -> [a]

null :: First a -> Bool

length :: First a -> Int

elem :: Eq a => a -> First a -> Bool

maximum :: Ord a => First a -> a

minimum :: Ord a => First a -> a

sum :: Num a => First a -> a

product :: Num a => First a -> a

Foldable Last

Since: base-4.8.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => Last m -> m

foldMap :: Monoid m => (a -> m) -> Last a -> m

foldMap' :: Monoid m => (a -> m) -> Last a -> m

foldr :: (a -> b -> b) -> b -> Last a -> b

foldr' :: (a -> b -> b) -> b -> Last a -> b

foldl :: (b -> a -> b) -> b -> Last a -> b

foldl' :: (b -> a -> b) -> b -> Last a -> b

foldr1 :: (a -> a -> a) -> Last a -> a

foldl1 :: (a -> a -> a) -> Last a -> a

toList :: Last a -> [a]

null :: Last a -> Bool

length :: Last a -> Int

elem :: Eq a => a -> Last a -> Bool

maximum :: Ord a => Last a -> a

minimum :: Ord a => Last a -> a

sum :: Num a => Last a -> a

product :: Num a => Last a -> a

Foldable Down

Since: base-4.12.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => Down m -> m

foldMap :: Monoid m => (a -> m) -> Down a -> m

foldMap' :: Monoid m => (a -> m) -> Down a -> m

foldr :: (a -> b -> b) -> b -> Down a -> b

foldr' :: (a -> b -> b) -> b -> Down a -> b

foldl :: (b -> a -> b) -> b -> Down a -> b

foldl' :: (b -> a -> b) -> b -> Down a -> b

foldr1 :: (a -> a -> a) -> Down a -> a

foldl1 :: (a -> a -> a) -> Down a -> a

toList :: Down a -> [a]

null :: Down a -> Bool

length :: Down a -> Int

elem :: Eq a => a -> Down a -> Bool

maximum :: Ord a => Down a -> a

minimum :: Ord a => Down a -> a

sum :: Num a => Down a -> a

product :: Num a => Down a -> a

Foldable First

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

fold :: Monoid m => First m -> m

foldMap :: Monoid m => (a -> m) -> First a -> m

foldMap' :: Monoid m => (a -> m) -> First a -> m

foldr :: (a -> b -> b) -> b -> First a -> b

foldr' :: (a -> b -> b) -> b -> First a -> b

foldl :: (b -> a -> b) -> b -> First a -> b

foldl' :: (b -> a -> b) -> b -> First a -> b

foldr1 :: (a -> a -> a) -> First a -> a

foldl1 :: (a -> a -> a) -> First a -> a

toList :: First a -> [a]

null :: First a -> Bool

length :: First a -> Int

elem :: Eq a => a -> First a -> Bool

maximum :: Ord a => First a -> a

minimum :: Ord a => First a -> a

sum :: Num a => First a -> a

product :: Num a => First a -> a

Foldable Last

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

fold :: Monoid m => Last m -> m

foldMap :: Monoid m => (a -> m) -> Last a -> m

foldMap' :: Monoid m => (a -> m) -> Last a -> m

foldr :: (a -> b -> b) -> b -> Last a -> b

foldr' :: (a -> b -> b) -> b -> Last a -> b

foldl :: (b -> a -> b) -> b -> Last a -> b

foldl' :: (b -> a -> b) -> b -> Last a -> b

foldr1 :: (a -> a -> a) -> Last a -> a

foldl1 :: (a -> a -> a) -> Last a -> a

toList :: Last a -> [a]

null :: Last a -> Bool

length :: Last a -> Int

elem :: Eq a => a -> Last a -> Bool

maximum :: Ord a => Last a -> a

minimum :: Ord a => Last a -> a

sum :: Num a => Last a -> a

product :: Num a => Last a -> a

Foldable Max

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

fold :: Monoid m => Max m -> m

foldMap :: Monoid m => (a -> m) -> Max a -> m

foldMap' :: Monoid m => (a -> m) -> Max a -> m

foldr :: (a -> b -> b) -> b -> Max a -> b

foldr' :: (a -> b -> b) -> b -> Max a -> b

foldl :: (b -> a -> b) -> b -> Max a -> b

foldl' :: (b -> a -> b) -> b -> Max a -> b

foldr1 :: (a -> a -> a) -> Max a -> a

foldl1 :: (a -> a -> a) -> Max a -> a

toList :: Max a -> [a]

null :: Max a -> Bool

length :: Max a -> Int

elem :: Eq a => a -> Max a -> Bool

maximum :: Ord a => Max a -> a

minimum :: Ord a => Max a -> a

sum :: Num a => Max a -> a

product :: Num a => Max a -> a

Foldable Min

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

fold :: Monoid m => Min m -> m

foldMap :: Monoid m => (a -> m) -> Min a -> m

foldMap' :: Monoid m => (a -> m) -> Min a -> m

foldr :: (a -> b -> b) -> b -> Min a -> b

foldr' :: (a -> b -> b) -> b -> Min a -> b

foldl :: (b -> a -> b) -> b -> Min a -> b

foldl' :: (b -> a -> b) -> b -> Min a -> b

foldr1 :: (a -> a -> a) -> Min a -> a

foldl1 :: (a -> a -> a) -> Min a -> a

toList :: Min a -> [a]

null :: Min a -> Bool

length :: Min a -> Int

elem :: Eq a => a -> Min a -> Bool

maximum :: Ord a => Min a -> a

minimum :: Ord a => Min a -> a

sum :: Num a => Min a -> a

product :: Num a => Min a -> a

Foldable Dual

Since: base-4.8.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => Dual m -> m

foldMap :: Monoid m => (a -> m) -> Dual a -> m

foldMap' :: Monoid m => (a -> m) -> Dual a -> m

foldr :: (a -> b -> b) -> b -> Dual a -> b

foldr' :: (a -> b -> b) -> b -> Dual a -> b

foldl :: (b -> a -> b) -> b -> Dual a -> b

foldl' :: (b -> a -> b) -> b -> Dual a -> b

foldr1 :: (a -> a -> a) -> Dual a -> a

foldl1 :: (a -> a -> a) -> Dual a -> a

toList :: Dual a -> [a]

null :: Dual a -> Bool

length :: Dual a -> Int

elem :: Eq a => a -> Dual a -> Bool

maximum :: Ord a => Dual a -> a

minimum :: Ord a => Dual a -> a

sum :: Num a => Dual a -> a

product :: Num a => Dual a -> a

Foldable Product

Since: base-4.8.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => Product m -> m

foldMap :: Monoid m => (a -> m) -> Product a -> m

foldMap' :: Monoid m => (a -> m) -> Product a -> m

foldr :: (a -> b -> b) -> b -> Product a -> b

foldr' :: (a -> b -> b) -> b -> Product a -> b

foldl :: (b -> a -> b) -> b -> Product a -> b

foldl' :: (b -> a -> b) -> b -> Product a -> b

foldr1 :: (a -> a -> a) -> Product a -> a

foldl1 :: (a -> a -> a) -> Product a -> a

toList :: Product a -> [a]

null :: Product a -> Bool

length :: Product a -> Int

elem :: Eq a => a -> Product a -> Bool

maximum :: Ord a => Product a -> a

minimum :: Ord a => Product a -> a

sum :: Num a => Product a -> a

product :: Num a => Product a -> a

Foldable Sum

Since: base-4.8.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => Sum m -> m

foldMap :: Monoid m => (a -> m) -> Sum a -> m

foldMap' :: Monoid m => (a -> m) -> Sum a -> m

foldr :: (a -> b -> b) -> b -> Sum a -> b

foldr' :: (a -> b -> b) -> b -> Sum a -> b

foldl :: (b -> a -> b) -> b -> Sum a -> b

foldl' :: (b -> a -> b) -> b -> Sum a -> b

foldr1 :: (a -> a -> a) -> Sum a -> a

foldl1 :: (a -> a -> a) -> Sum a -> a

toList :: Sum a -> [a]

null :: Sum a -> Bool

length :: Sum a -> Int

elem :: Eq a => a -> Sum a -> Bool

maximum :: Ord a => Sum a -> a

minimum :: Ord a => Sum a -> a

sum :: Num a => Sum a -> a

product :: Num a => Sum a -> a

Foldable NonEmpty

Since: base-4.9.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => NonEmpty m -> m

foldMap :: Monoid m => (a -> m) -> NonEmpty a -> m

foldMap' :: Monoid m => (a -> m) -> NonEmpty a -> m

foldr :: (a -> b -> b) -> b -> NonEmpty a -> b

foldr' :: (a -> b -> b) -> b -> NonEmpty a -> b

foldl :: (b -> a -> b) -> b -> NonEmpty a -> b

foldl' :: (b -> a -> b) -> b -> NonEmpty a -> b

foldr1 :: (a -> a -> a) -> NonEmpty a -> a

foldl1 :: (a -> a -> a) -> NonEmpty a -> a

toList :: NonEmpty a -> [a]

null :: NonEmpty a -> Bool

length :: NonEmpty a -> Int

elem :: Eq a => a -> NonEmpty a -> Bool

maximum :: Ord a => NonEmpty a -> a

minimum :: Ord a => NonEmpty a -> a

sum :: Num a => NonEmpty a -> a

product :: Num a => NonEmpty a -> a

Foldable Par1

Since: base-4.9.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => Par1 m -> m

foldMap :: Monoid m => (a -> m) -> Par1 a -> m

foldMap' :: Monoid m => (a -> m) -> Par1 a -> m

foldr :: (a -> b -> b) -> b -> Par1 a -> b

foldr' :: (a -> b -> b) -> b -> Par1 a -> b

foldl :: (b -> a -> b) -> b -> Par1 a -> b

foldl' :: (b -> a -> b) -> b -> Par1 a -> b

foldr1 :: (a -> a -> a) -> Par1 a -> a

foldl1 :: (a -> a -> a) -> Par1 a -> a

toList :: Par1 a -> [a]

null :: Par1 a -> Bool

length :: Par1 a -> Int

elem :: Eq a => a -> Par1 a -> Bool

maximum :: Ord a => Par1 a -> a

minimum :: Ord a => Par1 a -> a

sum :: Num a => Par1 a -> a

product :: Num a => Par1 a -> a

Foldable IntMap

Folds in order of increasing key.

Defined in Data.IntMap.Internal

Methods

fold :: Monoid m => IntMap m -> m

foldMap :: Monoid m => (a -> m) -> IntMap a -> m

foldMap' :: Monoid m => (a -> m) -> IntMap a -> m

foldr :: (a -> b -> b) -> b -> IntMap a -> b

foldr' :: (a -> b -> b) -> b -> IntMap a -> b

foldl :: (b -> a -> b) -> b -> IntMap a -> b

foldl' :: (b -> a -> b) -> b -> IntMap a -> b

foldr1 :: (a -> a -> a) -> IntMap a -> a

foldl1 :: (a -> a -> a) -> IntMap a -> a

toList :: IntMap a -> [a]

null :: IntMap a -> Bool

length :: IntMap a -> Int

elem :: Eq a => a -> IntMap a -> Bool

maximum :: Ord a => IntMap a -> a

minimum :: Ord a => IntMap a -> a

sum :: Num a => IntMap a -> a

product :: Num a => IntMap a -> a

Foldable Digit

Defined in Data.Sequence.Internal

Methods

fold :: Monoid m => Digit m -> m

foldMap :: Monoid m => (a -> m) -> Digit a -> m

foldMap' :: Monoid m => (a -> m) -> Digit a -> m

foldr :: (a -> b -> b) -> b -> Digit a -> b

foldr' :: (a -> b -> b) -> b -> Digit a -> b

foldl :: (b -> a -> b) -> b -> Digit a -> b

foldl' :: (b -> a -> b) -> b -> Digit a -> b

foldr1 :: (a -> a -> a) -> Digit a -> a

foldl1 :: (a -> a -> a) -> Digit a -> a

toList :: Digit a -> [a]

null :: Digit a -> Bool

length :: Digit a -> Int

elem :: Eq a => a -> Digit a -> Bool

maximum :: Ord a => Digit a -> a

minimum :: Ord a => Digit a -> a

sum :: Num a => Digit a -> a

product :: Num a => Digit a -> a

Foldable Elem

Defined in Data.Sequence.Internal

Methods

fold :: Monoid m => Elem m -> m

foldMap :: Monoid m => (a -> m) -> Elem a -> m

foldMap' :: Monoid m => (a -> m) -> Elem a -> m

foldr :: (a -> b -> b) -> b -> Elem a -> b

foldr' :: (a -> b -> b) -> b -> Elem a -> b

foldl :: (b -> a -> b) -> b -> Elem a -> b

foldl' :: (b -> a -> b) -> b -> Elem a -> b

foldr1 :: (a -> a -> a) -> Elem a -> a

foldl1 :: (a -> a -> a) -> Elem a -> a

toList :: Elem a -> [a]

null :: Elem a -> Bool

length :: Elem a -> Int

elem :: Eq a => a -> Elem a -> Bool

maximum :: Ord a => Elem a -> a

minimum :: Ord a => Elem a -> a

sum :: Num a => Elem a -> a

product :: Num a => Elem a -> a

Foldable FingerTree

Defined in Data.Sequence.Internal

Methods

fold :: Monoid m => FingerTree m -> m

foldMap :: Monoid m => (a -> m) -> FingerTree a -> m

foldMap' :: Monoid m => (a -> m) -> FingerTree a -> m

foldr :: (a -> b -> b) -> b -> FingerTree a -> b

foldr' :: (a -> b -> b) -> b -> FingerTree a -> b

foldl :: (b -> a -> b) -> b -> FingerTree a -> b

foldl' :: (b -> a -> b) -> b -> FingerTree a -> b

foldr1 :: (a -> a -> a) -> FingerTree a -> a

foldl1 :: (a -> a -> a) -> FingerTree a -> a

toList :: FingerTree a -> [a]

null :: FingerTree a -> Bool

length :: FingerTree a -> Int

elem :: Eq a => a -> FingerTree a -> Bool

maximum :: Ord a => FingerTree a -> a

minimum :: Ord a => FingerTree a -> a

sum :: Num a => FingerTree a -> a

product :: Num a => FingerTree a -> a

Foldable Node

Defined in Data.Sequence.Internal

Methods

fold :: Monoid m => Node m -> m

foldMap :: Monoid m => (a -> m) -> Node a -> m

foldMap' :: Monoid m => (a -> m) -> Node a -> m

foldr :: (a -> b -> b) -> b -> Node a -> b

foldr' :: (a -> b -> b) -> b -> Node a -> b

foldl :: (b -> a -> b) -> b -> Node a -> b

foldl' :: (b -> a -> b) -> b -> Node a -> b

foldr1 :: (a -> a -> a) -> Node a -> a

foldl1 :: (a -> a -> a) -> Node a -> a

toList :: Node a -> [a]

null :: Node a -> Bool

length :: Node a -> Int

elem :: Eq a => a -> Node a -> Bool

maximum :: Ord a => Node a -> a

minimum :: Ord a => Node a -> a

sum :: Num a => Node a -> a

product :: Num a => Node a -> a

Foldable Seq

Defined in Data.Sequence.Internal

Methods

fold :: Monoid m => Seq m -> m

foldMap :: Monoid m => (a -> m) -> Seq a -> m

foldMap' :: Monoid m => (a -> m) -> Seq a -> m

foldr :: (a -> b -> b) -> b -> Seq a -> b

foldr' :: (a -> b -> b) -> b -> Seq a -> b

foldl :: (b -> a -> b) -> b -> Seq a -> b

foldl' :: (b -> a -> b) -> b -> Seq a -> b

foldr1 :: (a -> a -> a) -> Seq a -> a

foldl1 :: (a -> a -> a) -> Seq a -> a

toList :: Seq a -> [a]

null :: Seq a -> Bool

length :: Seq a -> Int

elem :: Eq a => a -> Seq a -> Bool

maximum :: Ord a => Seq a -> a

minimum :: Ord a => Seq a -> a

sum :: Num a => Seq a -> a

product :: Num a => Seq a -> a

Foldable ViewL

Defined in Data.Sequence.Internal

Methods

fold :: Monoid m => ViewL m -> m

foldMap :: Monoid m => (a -> m) -> ViewL a -> m

foldMap' :: Monoid m => (a -> m) -> ViewL a -> m

foldr :: (a -> b -> b) -> b -> ViewL a -> b

foldr' :: (a -> b -> b) -> b -> ViewL a -> b

foldl :: (b -> a -> b) -> b -> ViewL a -> b

foldl' :: (b -> a -> b) -> b -> ViewL a -> b

foldr1 :: (a -> a -> a) -> ViewL a -> a

foldl1 :: (a -> a -> a) -> ViewL a -> a

toList :: ViewL a -> [a]

null :: ViewL a -> Bool

length :: ViewL a -> Int

elem :: Eq a => a -> ViewL a -> Bool

maximum :: Ord a => ViewL a -> a

minimum :: Ord a => ViewL a -> a

sum :: Num a => ViewL a -> a

product :: Num a => ViewL a -> a

Foldable ViewR

Defined in Data.Sequence.Internal

Methods

fold :: Monoid m => ViewR m -> m

foldMap :: Monoid m => (a -> m) -> ViewR a -> m

foldMap' :: Monoid m => (a -> m) -> ViewR a -> m

foldr :: (a -> b -> b) -> b -> ViewR a -> b

foldr' :: (a -> b -> b) -> b -> ViewR a -> b

foldl :: (b -> a -> b) -> b -> ViewR a -> b

foldl' :: (b -> a -> b) -> b -> ViewR a -> b

foldr1 :: (a -> a -> a) -> ViewR a -> a

foldl1 :: (a -> a -> a) -> ViewR a -> a

toList :: ViewR a -> [a]

null :: ViewR a -> Bool

length :: ViewR a -> Int

elem :: Eq a => a -> ViewR a -> Bool

maximum :: Ord a => ViewR a -> a

minimum :: Ord a => ViewR a -> a

sum :: Num a => ViewR a -> a

product :: Num a => ViewR a -> a

Foldable Set

Folds in order of increasing key.

Defined in Data.Set.Internal

Methods

fold :: Monoid m => Set m -> m

foldMap :: Monoid m => (a -> m) -> Set a -> m

foldMap' :: Monoid m => (a -> m) -> Set a -> m

foldr :: (a -> b -> b) -> b -> Set a -> b

foldr' :: (a -> b -> b) -> b -> Set a -> b

foldl :: (b -> a -> b) -> b -> Set a -> b

foldl' :: (b -> a -> b) -> b -> Set a -> b

foldr1 :: (a -> a -> a) -> Set a -> a

foldl1 :: (a -> a -> a) -> Set a -> a

toList :: Set a -> [a]

null :: Set a -> Bool

length :: Set a -> Int

elem :: Eq a => a -> Set a -> Bool

maximum :: Ord a => Set a -> a

minimum :: Ord a => Set a -> a

sum :: Num a => Set a -> a

product :: Num a => Set a -> a

Foldable Tree

Folds in preorder

Defined in Data.Tree

Methods

fold :: Monoid m => Tree m -> m

foldMap :: Monoid m => (a -> m) -> Tree a -> m

foldMap' :: Monoid m => (a -> m) -> Tree a -> m

foldr :: (a -> b -> b) -> b -> Tree a -> b

foldr' :: (a -> b -> b) -> b -> Tree a -> b

foldl :: (b -> a -> b) -> b -> Tree a -> b

foldl' :: (b -> a -> b) -> b -> Tree a -> b

foldr1 :: (a -> a -> a) -> Tree a -> a

foldl1 :: (a -> a -> a) -> Tree a -> a

toList :: Tree a -> [a]

null :: Tree a -> Bool

length :: Tree a -> Int

elem :: Eq a => a -> Tree a -> Bool

maximum :: Ord a => Tree a -> a

minimum :: Ord a => Tree a -> a

sum :: Num a => Tree a -> a

product :: Num a => Tree a -> a

Foldable Hashed

Defined in Data.Hashable.Class

Methods

fold :: Monoid m => Hashed m -> m

foldMap :: Monoid m => (a -> m) -> Hashed a -> m

foldMap' :: Monoid m => (a -> m) -> Hashed a -> m

foldr :: (a -> b -> b) -> b -> Hashed a -> b

foldr' :: (a -> b -> b) -> b -> Hashed a -> b

foldl :: (b -> a -> b) -> b -> Hashed a -> b

foldl' :: (b -> a -> b) -> b -> Hashed a -> b

foldr1 :: (a -> a -> a) -> Hashed a -> a

foldl1 :: (a -> a -> a) -> Hashed a -> a

toList :: Hashed a -> [a]

null :: Hashed a -> Bool

length :: Hashed a -> Int

elem :: Eq a => a -> Hashed a -> Bool

maximum :: Ord a => Hashed a -> a

minimum :: Ord a => Hashed a -> a

sum :: Num a => Hashed a -> a

product :: Num a => Hashed a -> a

Foldable HashSet

Defined in Data.HashSet.Internal

Methods

fold :: Monoid m => HashSet m -> m

foldMap :: Monoid m => (a -> m) -> HashSet a -> m

foldMap' :: Monoid m => (a -> m) -> HashSet a -> m

foldr :: (a -> b -> b) -> b -> HashSet a -> b

foldr' :: (a -> b -> b) -> b -> HashSet a -> b

foldl :: (b -> a -> b) -> b -> HashSet a -> b

foldl' :: (b -> a -> b) -> b -> HashSet a -> b

foldr1 :: (a -> a -> a) -> HashSet a -> a

foldl1 :: (a -> a -> a) -> HashSet a -> a

toList :: HashSet a -> [a]

null :: HashSet a -> Bool

length :: HashSet a -> Int

elem :: Eq a => a -> HashSet a -> Bool

maximum :: Ord a => HashSet a -> a

minimum :: Ord a => HashSet a -> a

sum :: Num a => HashSet a -> a

product :: Num a => HashSet a -> a

Foldable Maybe

Since: base-2.1

Defined in Data.Foldable

Methods

fold :: Monoid m => Maybe m -> m

foldMap :: Monoid m => (a -> m) -> Maybe a -> m

foldMap' :: Monoid m => (a -> m) -> Maybe a -> m

foldr :: (a -> b -> b) -> b -> Maybe a -> b

foldr' :: (a -> b -> b) -> b -> Maybe a -> b

foldl :: (b -> a -> b) -> b -> Maybe a -> b

foldl' :: (b -> a -> b) -> b -> Maybe a -> b

foldr1 :: (a -> a -> a) -> Maybe a -> a

foldl1 :: (a -> a -> a) -> Maybe a -> a

toList :: Maybe a -> [a]

null :: Maybe a -> Bool

length :: Maybe a -> Int

elem :: Eq a => a -> Maybe a -> Bool

maximum :: Ord a => Maybe a -> a

minimum :: Ord a => Maybe a -> a

sum :: Num a => Maybe a -> a

product :: Num a => Maybe a -> a

Foldable Solo

Since: base-4.15

Defined in Data.Foldable

Methods

fold :: Monoid m => Solo m -> m

foldMap :: Monoid m => (a -> m) -> Solo a -> m

foldMap' :: Monoid m => (a -> m) -> Solo a -> m

foldr :: (a -> b -> b) -> b -> Solo a -> b

foldr' :: (a -> b -> b) -> b -> Solo a -> b

foldl :: (b -> a -> b) -> b -> Solo a -> b

foldl' :: (b -> a -> b) -> b -> Solo a -> b

foldr1 :: (a -> a -> a) -> Solo a -> a

foldl1 :: (a -> a -> a) -> Solo a -> a

toList :: Solo a -> [a]

null :: Solo a -> Bool

length :: Solo a -> Int

elem :: Eq a => a -> Solo a -> Bool

maximum :: Ord a => Solo a -> a

minimum :: Ord a => Solo a -> a

sum :: Num a => Solo a -> a

product :: Num a => Solo a -> a

Foldable List

Since: base-2.1

Defined in Data.Foldable

Methods

fold :: Monoid m => [m] -> m

foldMap :: Monoid m => (a -> m) -> [a] -> m

foldMap' :: Monoid m => (a -> m) -> [a] -> m

foldr :: (a -> b -> b) -> b -> [a] -> b

foldr' :: (a -> b -> b) -> b -> [a] -> b

foldl :: (b -> a -> b) -> b -> [a] -> b

foldl' :: (b -> a -> b) -> b -> [a] -> b

foldr1 :: (a -> a -> a) -> [a] -> a

foldl1 :: (a -> a -> a) -> [a] -> a

toList :: [a] -> [a]

null :: [a] -> Bool

length :: [a] -> Int

elem :: Eq a => a -> [a] -> Bool

maximum :: Ord a => [a] -> a

minimum :: Ord a => [a] -> a

sum :: Num a => [a] -> a

product :: Num a => [a] -> a

Foldable (Either a)

Since: base-4.7.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => Either a m -> m

foldMap :: Monoid m => (a0 -> m) -> Either a a0 -> m

foldMap' :: Monoid m => (a0 -> m) -> Either a a0 -> m

foldr :: (a0 -> b -> b) -> b -> Either a a0 -> b

foldr' :: (a0 -> b -> b) -> b -> Either a a0 -> b

foldl :: (b -> a0 -> b) -> b -> Either a a0 -> b

foldl' :: (b -> a0 -> b) -> b -> Either a a0 -> b

foldr1 :: (a0 -> a0 -> a0) -> Either a a0 -> a0

foldl1 :: (a0 -> a0 -> a0) -> Either a a0 -> a0

toList :: Either a a0 -> [a0]

null :: Either a a0 -> Bool

length :: Either a a0 -> Int

elem :: Eq a0 => a0 -> Either a a0 -> Bool

maximum :: Ord a0 => Either a a0 -> a0

minimum :: Ord a0 => Either a a0 -> a0

sum :: Num a0 => Either a a0 -> a0

product :: Num a0 => Either a a0 -> a0

Foldable (Proxy :: Type -> Type)

Since: base-4.7.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => Proxy m -> m

foldMap :: Monoid m => (a -> m) -> Proxy a -> m

foldMap' :: Monoid m => (a -> m) -> Proxy a -> m

foldr :: (a -> b -> b) -> b -> Proxy a -> b

foldr' :: (a -> b -> b) -> b -> Proxy a -> b

foldl :: (b -> a -> b) -> b -> Proxy a -> b

foldl' :: (b -> a -> b) -> b -> Proxy a -> b

foldr1 :: (a -> a -> a) -> Proxy a -> a

foldl1 :: (a -> a -> a) -> Proxy a -> a

toList :: Proxy a -> [a]

null :: Proxy a -> Bool

length :: Proxy a -> Int

elem :: Eq a => a -> Proxy a -> Bool

maximum :: Ord a => Proxy a -> a

minimum :: Ord a => Proxy a -> a

sum :: Num a => Proxy a -> a

product :: Num a => Proxy a -> a

Foldable (Arg a)

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

fold :: Monoid m => Arg a m -> m

foldMap :: Monoid m => (a0 -> m) -> Arg a a0 -> m

foldMap' :: Monoid m => (a0 -> m) -> Arg a a0 -> m

foldr :: (a0 -> b -> b) -> b -> Arg a a0 -> b

foldr' :: (a0 -> b -> b) -> b -> Arg a a0 -> b

foldl :: (b -> a0 -> b) -> b -> Arg a a0 -> b

foldl' :: (b -> a0 -> b) -> b -> Arg a a0 -> b

foldr1 :: (a0 -> a0 -> a0) -> Arg a a0 -> a0

foldl1 :: (a0 -> a0 -> a0) -> Arg a a0 -> a0

toList :: Arg a a0 -> [a0]

null :: Arg a a0 -> Bool

length :: Arg a a0 -> Int

elem :: Eq a0 => a0 -> Arg a a0 -> Bool

maximum :: Ord a0 => Arg a a0 -> a0

minimum :: Ord a0 => Arg a a0 -> a0

sum :: Num a0 => Arg a a0 -> a0

product :: Num a0 => Arg a a0 -> a0

Foldable (Array i)

Since: base-4.8.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => Array i m -> m

foldMap :: Monoid m => (a -> m) -> Array i a -> m

foldMap' :: Monoid m => (a -> m) -> Array i a -> m

foldr :: (a -> b -> b) -> b -> Array i a -> b

foldr' :: (a -> b -> b) -> b -> Array i a -> b

foldl :: (b -> a -> b) -> b -> Array i a -> b

foldl' :: (b -> a -> b) -> b -> Array i a -> b

foldr1 :: (a -> a -> a) -> Array i a -> a

foldl1 :: (a -> a -> a) -> Array i a -> a

toList :: Array i a -> [a]

null :: Array i a -> Bool

length :: Array i a -> Int

elem :: Eq a => a -> Array i a -> Bool

maximum :: Ord a => Array i a -> a

minimum :: Ord a => Array i a -> a

sum :: Num a => Array i a -> a

product :: Num a => Array i a -> a

Foldable (U1 :: Type -> Type)

Since: base-4.9.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => U1 m -> m

foldMap :: Monoid m => (a -> m) -> U1 a -> m

foldMap' :: Monoid m => (a -> m) -> U1 a -> m

foldr :: (a -> b -> b) -> b -> U1 a -> b

foldr' :: (a -> b -> b) -> b -> U1 a -> b

foldl :: (b -> a -> b) -> b -> U1 a -> b

foldl' :: (b -> a -> b) -> b -> U1 a -> b

foldr1 :: (a -> a -> a) -> U1 a -> a

foldl1 :: (a -> a -> a) -> U1 a -> a

toList :: U1 a -> [a]

null :: U1 a -> Bool

length :: U1 a -> Int

elem :: Eq a => a -> U1 a -> Bool

maximum :: Ord a => U1 a -> a

minimum :: Ord a => U1 a -> a

sum :: Num a => U1 a -> a

product :: Num a => U1 a -> a

Foldable (UAddr :: Type -> Type)

Since: base-4.9.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => UAddr m -> m

foldMap :: Monoid m => (a -> m) -> UAddr a -> m

foldMap' :: Monoid m => (a -> m) -> UAddr a -> m

foldr :: (a -> b -> b) -> b -> UAddr a -> b

foldr' :: (a -> b -> b) -> b -> UAddr a -> b

foldl :: (b -> a -> b) -> b -> UAddr a -> b

foldl' :: (b -> a -> b) -> b -> UAddr a -> b

foldr1 :: (a -> a -> a) -> UAddr a -> a

foldl1 :: (a -> a -> a) -> UAddr a -> a

toList :: UAddr a -> [a]

null :: UAddr a -> Bool

length :: UAddr a -> Int

elem :: Eq a => a -> UAddr a -> Bool

maximum :: Ord a => UAddr a -> a

minimum :: Ord a => UAddr a -> a

sum :: Num a => UAddr a -> a

product :: Num a => UAddr a -> a

Foldable (UChar :: Type -> Type)

Since: base-4.9.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => UChar m -> m

foldMap :: Monoid m => (a -> m) -> UChar a -> m

foldMap' :: Monoid m => (a -> m) -> UChar a -> m

foldr :: (a -> b -> b) -> b -> UChar a -> b

foldr' :: (a -> b -> b) -> b -> UChar a -> b

foldl :: (b -> a -> b) -> b -> UChar a -> b

foldl' :: (b -> a -> b) -> b -> UChar a -> b

foldr1 :: (a -> a -> a) -> UChar a -> a

foldl1 :: (a -> a -> a) -> UChar a -> a

toList :: UChar a -> [a]

null :: UChar a -> Bool

length :: UChar a -> Int

elem :: Eq a => a -> UChar a -> Bool

maximum :: Ord a => UChar a -> a

minimum :: Ord a => UChar a -> a

sum :: Num a => UChar a -> a

product :: Num a => UChar a -> a

Foldable (UDouble :: Type -> Type)

Since: base-4.9.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => UDouble m -> m

foldMap :: Monoid m => (a -> m) -> UDouble a -> m

foldMap' :: Monoid m => (a -> m) -> UDouble a -> m

foldr :: (a -> b -> b) -> b -> UDouble a -> b

foldr' :: (a -> b -> b) -> b -> UDouble a -> b

foldl :: (b -> a -> b) -> b -> UDouble a -> b

foldl' :: (b -> a -> b) -> b -> UDouble a -> b

foldr1 :: (a -> a -> a) -> UDouble a -> a

foldl1 :: (a -> a -> a) -> UDouble a -> a

toList :: UDouble a -> [a]

null :: UDouble a -> Bool

length :: UDouble a -> Int

elem :: Eq a => a -> UDouble a -> Bool

maximum :: Ord a => UDouble a -> a

minimum :: Ord a => UDouble a -> a

sum :: Num a => UDouble a -> a

product :: Num a => UDouble a -> a

Foldable (UFloat :: Type -> Type)

Since: base-4.9.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => UFloat m -> m

foldMap :: Monoid m => (a -> m) -> UFloat a -> m

foldMap' :: Monoid m => (a -> m) -> UFloat a -> m

foldr :: (a -> b -> b) -> b -> UFloat a -> b

foldr' :: (a -> b -> b) -> b -> UFloat a -> b

foldl :: (b -> a -> b) -> b -> UFloat a -> b

foldl' :: (b -> a -> b) -> b -> UFloat a -> b

foldr1 :: (a -> a -> a) -> UFloat a -> a

foldl1 :: (a -> a -> a) -> UFloat a -> a

toList :: UFloat a -> [a]

null :: UFloat a -> Bool

length :: UFloat a -> Int

elem :: Eq a => a -> UFloat a -> Bool

maximum :: Ord a => UFloat a -> a

minimum :: Ord a => UFloat a -> a

sum :: Num a => UFloat a -> a

product :: Num a => UFloat a -> a

Foldable (UInt :: Type -> Type)

Since: base-4.9.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => UInt m -> m

foldMap :: Monoid m => (a -> m) -> UInt a -> m

foldMap' :: Monoid m => (a -> m) -> UInt a -> m

foldr :: (a -> b -> b) -> b -> UInt a -> b

foldr' :: (a -> b -> b) -> b -> UInt a -> b

foldl :: (b -> a -> b) -> b -> UInt a -> b

foldl' :: (b -> a -> b) -> b -> UInt a -> b

foldr1 :: (a -> a -> a) -> UInt a -> a

foldl1 :: (a -> a -> a) -> UInt a -> a

toList :: UInt a -> [a]

null :: UInt a -> Bool

length :: UInt a -> Int

elem :: Eq a => a -> UInt a -> Bool

maximum :: Ord a => UInt a -> a

minimum :: Ord a => UInt a -> a

sum :: Num a => UInt a -> a

product :: Num a => UInt a -> a

Foldable (UWord :: Type -> Type)

Since: base-4.9.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => UWord m -> m

foldMap :: Monoid m => (a -> m) -> UWord a -> m

foldMap' :: Monoid m => (a -> m) -> UWord a -> m

foldr :: (a -> b -> b) -> b -> UWord a -> b

foldr' :: (a -> b -> b) -> b -> UWord a -> b

foldl :: (b -> a -> b) -> b -> UWord a -> b

foldl' :: (b -> a -> b) -> b -> UWord a -> b

foldr1 :: (a -> a -> a) -> UWord a -> a

foldl1 :: (a -> a -> a) -> UWord a -> a

toList :: UWord a -> [a]

null :: UWord a -> Bool

length :: UWord a -> Int

elem :: Eq a => a -> UWord a -> Bool

maximum :: Ord a => UWord a -> a

minimum :: Ord a => UWord a -> a

sum :: Num a => UWord a -> a

product :: Num a => UWord a -> a

Foldable (V1 :: Type -> Type)

Since: base-4.9.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => V1 m -> m

foldMap :: Monoid m => (a -> m) -> V1 a -> m

foldMap' :: Monoid m => (a -> m) -> V1 a -> m

foldr :: (a -> b -> b) -> b -> V1 a -> b

foldr' :: (a -> b -> b) -> b -> V1 a -> b

foldl :: (b -> a -> b) -> b -> V1 a -> b

foldl' :: (b -> a -> b) -> b -> V1 a -> b

foldr1 :: (a -> a -> a) -> V1 a -> a

foldl1 :: (a -> a -> a) -> V1 a -> a

toList :: V1 a -> [a]

null :: V1 a -> Bool

length :: V1 a -> Int

elem :: Eq a => a -> V1 a -> Bool

maximum :: Ord a => V1 a -> a

minimum :: Ord a => V1 a -> a

sum :: Num a => V1 a -> a

product :: Num a => V1 a -> a

Foldable (Map k)

Folds in order of increasing key.

Defined in Data.Map.Internal

Methods

fold :: Monoid m => Map k m -> m

foldMap :: Monoid m => (a -> m) -> Map k a -> m

foldMap' :: Monoid m => (a -> m) -> Map k a -> m

foldr :: (a -> b -> b) -> b -> Map k a -> b

foldr' :: (a -> b -> b) -> b -> Map k a -> b

foldl :: (b -> a -> b) -> b -> Map k a -> b

foldl' :: (b -> a -> b) -> b -> Map k a -> b

foldr1 :: (a -> a -> a) -> Map k a -> a

foldl1 :: (a -> a -> a) -> Map k a -> a

toList :: Map k a -> [a]

null :: Map k a -> Bool

length :: Map k a -> Int

elem :: Eq a => a -> Map k a -> Bool

maximum :: Ord a => Map k a -> a

minimum :: Ord a => Map k a -> a

sum :: Num a => Map k a -> a

product :: Num a => Map k a -> a

Foldable (HashMap k)

Defined in Data.HashMap.Internal

Methods

fold :: Monoid m => HashMap k m -> m

foldMap :: Monoid m => (a -> m) -> HashMap k a -> m

foldMap' :: Monoid m => (a -> m) -> HashMap k a -> m

foldr :: (a -> b -> b) -> b -> HashMap k a -> b

foldr' :: (a -> b -> b) -> b -> HashMap k a -> b

foldl :: (b -> a -> b) -> b -> HashMap k a -> b

foldl' :: (b -> a -> b) -> b -> HashMap k a -> b

foldr1 :: (a -> a -> a) -> HashMap k a -> a

foldl1 :: (a -> a -> a) -> HashMap k a -> a

toList :: HashMap k a -> [a]

null :: HashMap k a -> Bool

length :: HashMap k a -> Int

elem :: Eq a => a -> HashMap k a -> Bool

maximum :: Ord a => HashMap k a -> a

minimum :: Ord a => HashMap k a -> a

sum :: Num a => HashMap k a -> a

product :: Num a => HashMap k a -> a

Foldable f => Foldable (MaybeT f)

Defined in Control.Monad.Trans.Maybe

Methods

fold :: Monoid m => MaybeT f m -> m

foldMap :: Monoid m => (a -> m) -> MaybeT f a -> m

foldMap' :: Monoid m => (a -> m) -> MaybeT f a -> m

foldr :: (a -> b -> b) -> b -> MaybeT f a -> b

foldr' :: (a -> b -> b) -> b -> MaybeT f a -> b

foldl :: (b -> a -> b) -> b -> MaybeT f a -> b

foldl' :: (b -> a -> b) -> b -> MaybeT f a -> b

foldr1 :: (a -> a -> a) -> MaybeT f a -> a

foldl1 :: (a -> a -> a) -> MaybeT f a -> a

toList :: MaybeT f a -> [a]

null :: MaybeT f a -> Bool

length :: MaybeT f a -> Int

elem :: Eq a => a -> MaybeT f a -> Bool

maximum :: Ord a => MaybeT f a -> a

minimum :: Ord a => MaybeT f a -> a

sum :: Num a => MaybeT f a -> a

product :: Num a => MaybeT f a -> a

Foldable ((,) a)

Since: base-4.7.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => (a, m) -> m

foldMap :: Monoid m => (a0 -> m) -> (a, a0) -> m

foldMap' :: Monoid m => (a0 -> m) -> (a, a0) -> m

foldr :: (a0 -> b -> b) -> b -> (a, a0) -> b

foldr' :: (a0 -> b -> b) -> b -> (a, a0) -> b

foldl :: (b -> a0 -> b) -> b -> (a, a0) -> b

foldl' :: (b -> a0 -> b) -> b -> (a, a0) -> b

foldr1 :: (a0 -> a0 -> a0) -> (a, a0) -> a0

foldl1 :: (a0 -> a0 -> a0) -> (a, a0) -> a0

toList :: (a, a0) -> [a0]

null :: (a, a0) -> Bool

length :: (a, a0) -> Int

elem :: Eq a0 => a0 -> (a, a0) -> Bool

maximum :: Ord a0 => (a, a0) -> a0

minimum :: Ord a0 => (a, a0) -> a0

sum :: Num a0 => (a, a0) -> a0

product :: Num a0 => (a, a0) -> a0

Foldable (Const m :: Type -> Type)

Since: base-4.7.0.0

Defined in Data.Functor.Const

Methods

fold :: Monoid m0 => Const m m0 -> m0

foldMap :: Monoid m0 => (a -> m0) -> Const m a -> m0

foldMap' :: Monoid m0 => (a -> m0) -> Const m a -> m0

foldr :: (a -> b -> b) -> b -> Const m a -> b

foldr' :: (a -> b -> b) -> b -> Const m a -> b

foldl :: (b -> a -> b) -> b -> Const m a -> b

foldl' :: (b -> a -> b) -> b -> Const m a -> b

foldr1 :: (a -> a -> a) -> Const m a -> a

foldl1 :: (a -> a -> a) -> Const m a -> a

toList :: Const m a -> [a]

null :: Const m a -> Bool

length :: Const m a -> Int

elem :: Eq a => a -> Const m a -> Bool

maximum :: Ord a => Const m a -> a

minimum :: Ord a => Const m a -> a

sum :: Num a => Const m a -> a

product :: Num a => Const m a -> a

Foldable f => Foldable (Ap f)

Since: base-4.12.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => Ap f m -> m

foldMap :: Monoid m => (a -> m) -> Ap f a -> m

foldMap' :: Monoid m => (a -> m) -> Ap f a -> m

foldr :: (a -> b -> b) -> b -> Ap f a -> b

foldr' :: (a -> b -> b) -> b -> Ap f a -> b

foldl :: (b -> a -> b) -> b -> Ap f a -> b

foldl' :: (b -> a -> b) -> b -> Ap f a -> b

foldr1 :: (a -> a -> a) -> Ap f a -> a

foldl1 :: (a -> a -> a) -> Ap f a -> a

toList :: Ap f a -> [a]

null :: Ap f a -> Bool

length :: Ap f a -> Int

elem :: Eq a => a -> Ap f a -> Bool

maximum :: Ord a => Ap f a -> a

minimum :: Ord a => Ap f a -> a

sum :: Num a => Ap f a -> a

product :: Num a => Ap f a -> a

Foldable f => Foldable (Alt f)

Since: base-4.12.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => Alt f m -> m

foldMap :: Monoid m => (a -> m) -> Alt f a -> m

foldMap' :: Monoid m => (a -> m) -> Alt f a -> m

foldr :: (a -> b -> b) -> b -> Alt f a -> b

foldr' :: (a -> b -> b) -> b -> Alt f a -> b

foldl :: (b -> a -> b) -> b -> Alt f a -> b

foldl' :: (b -> a -> b) -> b -> Alt f a -> b

foldr1 :: (a -> a -> a) -> Alt f a -> a

foldl1 :: (a -> a -> a) -> Alt f a -> a

toList :: Alt f a -> [a]

null :: Alt f a -> Bool

length :: Alt f a -> Int

elem :: Eq a => a -> Alt f a -> Bool

maximum :: Ord a => Alt f a -> a

minimum :: Ord a => Alt f a -> a

sum :: Num a => Alt f a -> a

product :: Num a => Alt f a -> a

Foldable f => Foldable (Rec1 f)

Since: base-4.9.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => Rec1 f m -> m

foldMap :: Monoid m => (a -> m) -> Rec1 f a -> m

foldMap' :: Monoid m => (a -> m) -> Rec1 f a -> m

foldr :: (a -> b -> b) -> b -> Rec1 f a -> b

foldr' :: (a -> b -> b) -> b -> Rec1 f a -> b

foldl :: (b -> a -> b) -> b -> Rec1 f a -> b

foldl' :: (b -> a -> b) -> b -> Rec1 f a -> b

foldr1 :: (a -> a -> a) -> Rec1 f a -> a

foldl1 :: (a -> a -> a) -> Rec1 f a -> a

toList :: Rec1 f a -> [a]

null :: Rec1 f a -> Bool

length :: Rec1 f a -> Int

elem :: Eq a => a -> Rec1 f a -> Bool

maximum :: Ord a => Rec1 f a -> a

minimum :: Ord a => Rec1 f a -> a

sum :: Num a => Rec1 f a -> a

product :: Num a => Rec1 f a -> a

Foldable f => Foldable (ExceptT e f)

Defined in Control.Monad.Trans.Except

Methods

fold :: Monoid m => ExceptT e f m -> m

foldMap :: Monoid m => (a -> m) -> ExceptT e f a -> m

foldMap' :: Monoid m => (a -> m) -> ExceptT e f a -> m

foldr :: (a -> b -> b) -> b -> ExceptT e f a -> b

foldr' :: (a -> b -> b) -> b -> ExceptT e f a -> b

foldl :: (b -> a -> b) -> b -> ExceptT e f a -> b

foldl' :: (b -> a -> b) -> b -> ExceptT e f a -> b

foldr1 :: (a -> a -> a) -> ExceptT e f a -> a

foldl1 :: (a -> a -> a) -> ExceptT e f a -> a

toList :: ExceptT e f a -> [a]

null :: ExceptT e f a -> Bool

length :: ExceptT e f a -> Int

elem :: Eq a => a -> ExceptT e f a -> Bool

maximum :: Ord a => ExceptT e f a -> a

minimum :: Ord a => ExceptT e f a -> a

sum :: Num a => ExceptT e f a -> a

product :: Num a => ExceptT e f a -> a

Foldable f => Foldable (IdentityT f)

Defined in Control.Monad.Trans.Identity

Methods

fold :: Monoid m => IdentityT f m -> m

foldMap :: Monoid m => (a -> m) -> IdentityT f a -> m

foldMap' :: Monoid m => (a -> m) -> IdentityT f a -> m

foldr :: (a -> b -> b) -> b -> IdentityT f a -> b

foldr' :: (a -> b -> b) -> b -> IdentityT f a -> b

foldl :: (b -> a -> b) -> b -> IdentityT f a -> b

foldl' :: (b -> a -> b) -> b -> IdentityT f a -> b

foldr1 :: (a -> a -> a) -> IdentityT f a -> a

foldl1 :: (a -> a -> a) -> IdentityT f a -> a

toList :: IdentityT f a -> [a]

null :: IdentityT f a -> Bool

length :: IdentityT f a -> Int

elem :: Eq a => a -> IdentityT f a -> Bool

maximum :: Ord a => IdentityT f a -> a

minimum :: Ord a => IdentityT f a -> a

sum :: Num a => IdentityT f a -> a

product :: Num a => IdentityT f a -> a

Foldable f => Foldable (WriterT w f)

Defined in Control.Monad.Trans.Writer.Lazy

Methods

fold :: Monoid m => WriterT w f m -> m

foldMap :: Monoid m => (a -> m) -> WriterT w f a -> m

foldMap' :: Monoid m => (a -> m) -> WriterT w f a -> m

foldr :: (a -> b -> b) -> b -> WriterT w f a -> b

foldr' :: (a -> b -> b) -> b -> WriterT w f a -> b

foldl :: (b -> a -> b) -> b -> WriterT w f a -> b

foldl' :: (b -> a -> b) -> b -> WriterT w f a -> b

foldr1 :: (a -> a -> a) -> WriterT w f a -> a

foldl1 :: (a -> a -> a) -> WriterT w f a -> a

toList :: WriterT w f a -> [a]

null :: WriterT w f a -> Bool

length :: WriterT w f a -> Int

elem :: Eq a => a -> WriterT w f a -> Bool

maximum :: Ord a => WriterT w f a -> a

minimum :: Ord a => WriterT w f a -> a

sum :: Num a => WriterT w f a -> a

product :: Num a => WriterT w f a -> a

Foldable f => Foldable (WriterT w f)

Defined in Control.Monad.Trans.Writer.Strict

Methods

fold :: Monoid m => WriterT w f m -> m

foldMap :: Monoid m => (a -> m) -> WriterT w f a -> m

foldMap' :: Monoid m => (a -> m) -> WriterT w f a -> m

foldr :: (a -> b -> b) -> b -> WriterT w f a -> b

foldr' :: (a -> b -> b) -> b -> WriterT w f a -> b

foldl :: (b -> a -> b) -> b -> WriterT w f a -> b

foldl' :: (b -> a -> b) -> b -> WriterT w f a -> b

foldr1 :: (a -> a -> a) -> WriterT w f a -> a

foldl1 :: (a -> a -> a) -> WriterT w f a -> a

toList :: WriterT w f a -> [a]

null :: WriterT w f a -> Bool

length :: WriterT w f a -> Int

elem :: Eq a => a -> WriterT w f a -> Bool

maximum :: Ord a => WriterT w f a -> a

minimum :: Ord a => WriterT w f a -> a

sum :: Num a => WriterT w f a -> a

product :: Num a => WriterT w f a -> a

(Foldable f, Foldable g) => Foldable (Product f g)

Since: base-4.9.0.0

Defined in Data.Functor.Product

Methods

fold :: Monoid m => Product f g m -> m

foldMap :: Monoid m => (a -> m) -> Product f g a -> m

foldMap' :: Monoid m => (a -> m) -> Product f g a -> m

foldr :: (a -> b -> b) -> b -> Product f g a -> b

foldr' :: (a -> b -> b) -> b -> Product f g a -> b

foldl :: (b -> a -> b) -> b -> Product f g a -> b

foldl' :: (b -> a -> b) -> b -> Product f g a -> b

foldr1 :: (a -> a -> a) -> Product f g a -> a

foldl1 :: (a -> a -> a) -> Product f g a -> a

toList :: Product f g a -> [a]

null :: Product f g a -> Bool

length :: Product f g a -> Int

elem :: Eq a => a -> Product f g a -> Bool

maximum :: Ord a => Product f g a -> a

minimum :: Ord a => Product f g a -> a

sum :: Num a => Product f g a -> a

product :: Num a => Product f g a -> a

(Foldable f, Foldable g) => Foldable (Sum f g)

Since: base-4.9.0.0

Defined in Data.Functor.Sum

Methods

fold :: Monoid m => Sum f g m -> m

foldMap :: Monoid m => (a -> m) -> Sum f g a -> m

foldMap' :: Monoid m => (a -> m) -> Sum f g a -> m

foldr :: (a -> b -> b) -> b -> Sum f g a -> b

foldr' :: (a -> b -> b) -> b -> Sum f g a -> b

foldl :: (b -> a -> b) -> b -> Sum f g a -> b

foldl' :: (b -> a -> b) -> b -> Sum f g a -> b

foldr1 :: (a -> a -> a) -> Sum f g a -> a

foldl1 :: (a -> a -> a) -> Sum f g a -> a

toList :: Sum f g a -> [a]

null :: Sum f g a -> Bool

length :: Sum f g a -> Int

elem :: Eq a => a -> Sum f g a -> Bool

maximum :: Ord a => Sum f g a -> a

minimum :: Ord a => Sum f g a -> a

sum :: Num a => Sum f g a -> a

product :: Num a => Sum f g a -> a

(Foldable f, Foldable g) => Foldable (f :*: g)

Since: base-4.9.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => (f :*: g) m -> m

foldMap :: Monoid m => (a -> m) -> (f :*: g) a -> m

foldMap' :: Monoid m => (a -> m) -> (f :*: g) a -> m

foldr :: (a -> b -> b) -> b -> (f :*: g) a -> b

foldr' :: (a -> b -> b) -> b -> (f :*: g) a -> b

foldl :: (b -> a -> b) -> b -> (f :*: g) a -> b

foldl' :: (b -> a -> b) -> b -> (f :*: g) a -> b

foldr1 :: (a -> a -> a) -> (f :*: g) a -> a

foldl1 :: (a -> a -> a) -> (f :*: g) a -> a

toList :: (f :*: g) a -> [a]

null :: (f :*: g) a -> Bool

length :: (f :*: g) a -> Int

elem :: Eq a => a -> (f :*: g) a -> Bool

maximum :: Ord a => (f :*: g) a -> a

minimum :: Ord a => (f :*: g) a -> a

sum :: Num a => (f :*: g) a -> a

product :: Num a => (f :*: g) a -> a

(Foldable f, Foldable g) => Foldable (f :+: g)

Since: base-4.9.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => (f :+: g) m -> m

foldMap :: Monoid m => (a -> m) -> (f :+: g) a -> m

foldMap' :: Monoid m => (a -> m) -> (f :+: g) a -> m

foldr :: (a -> b -> b) -> b -> (f :+: g) a -> b

foldr' :: (a -> b -> b) -> b -> (f :+: g) a -> b

foldl :: (b -> a -> b) -> b -> (f :+: g) a -> b

foldl' :: (b -> a -> b) -> b -> (f :+: g) a -> b

foldr1 :: (a -> a -> a) -> (f :+: g) a -> a

foldl1 :: (a -> a -> a) -> (f :+: g) a -> a

toList :: (f :+: g) a -> [a]

null :: (f :+: g) a -> Bool

length :: (f :+: g) a -> Int

elem :: Eq a => a -> (f :+: g) a -> Bool

maximum :: Ord a => (f :+: g) a -> a

minimum :: Ord a => (f :+: g) a -> a

sum :: Num a => (f :+: g) a -> a

product :: Num a => (f :+: g) a -> a

Foldable (K1 i c :: Type -> Type)

Since: base-4.9.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => K1 i c m -> m

foldMap :: Monoid m => (a -> m) -> K1 i c a -> m

foldMap' :: Monoid m => (a -> m) -> K1 i c a -> m

foldr :: (a -> b -> b) -> b -> K1 i c a -> b

foldr' :: (a -> b -> b) -> b -> K1 i c a -> b

foldl :: (b -> a -> b) -> b -> K1 i c a -> b

foldl' :: (b -> a -> b) -> b -> K1 i c a -> b

foldr1 :: (a -> a -> a) -> K1 i c a -> a

foldl1 :: (a -> a -> a) -> K1 i c a -> a

toList :: K1 i c a -> [a]

null :: K1 i c a -> Bool

length :: K1 i c a -> Int

elem :: Eq a => a -> K1 i c a -> Bool

maximum :: Ord a => K1 i c a -> a

minimum :: Ord a => K1 i c a -> a

sum :: Num a => K1 i c a -> a

product :: Num a => K1 i c a -> a

(Foldable f, Foldable g) => Foldable (Compose f g)

Since: base-4.9.0.0

Defined in Data.Functor.Compose

Methods

fold :: Monoid m => Compose f g m -> m

foldMap :: Monoid m => (a -> m) -> Compose f g a -> m

foldMap' :: Monoid m => (a -> m) -> Compose f g a -> m

foldr :: (a -> b -> b) -> b -> Compose f g a -> b

foldr' :: (a -> b -> b) -> b -> Compose f g a -> b

foldl :: (b -> a -> b) -> b -> Compose f g a -> b

foldl' :: (b -> a -> b) -> b -> Compose f g a -> b

foldr1 :: (a -> a -> a) -> Compose f g a -> a

foldl1 :: (a -> a -> a) -> Compose f g a -> a

toList :: Compose f g a -> [a]

null :: Compose f g a -> Bool

length :: Compose f g a -> Int

elem :: Eq a => a -> Compose f g a -> Bool

maximum :: Ord a => Compose f g a -> a

minimum :: Ord a => Compose f g a -> a

sum :: Num a => Compose f g a -> a

product :: Num a => Compose f g a -> a

(Foldable f, Foldable g) => Foldable (f :.: g)

Since: base-4.9.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => (f :.: g) m -> m

foldMap :: Monoid m => (a -> m) -> (f :.: g) a -> m

foldMap' :: Monoid m => (a -> m) -> (f :.: g) a -> m

foldr :: (a -> b -> b) -> b -> (f :.: g) a -> b

foldr' :: (a -> b -> b) -> b -> (f :.: g) a -> b

foldl :: (b -> a -> b) -> b -> (f :.: g) a -> b

foldl' :: (b -> a -> b) -> b -> (f :.: g) a -> b

foldr1 :: (a -> a -> a) -> (f :.: g) a -> a

foldl1 :: (a -> a -> a) -> (f :.: g) a -> a

toList :: (f :.: g) a -> [a]

null :: (f :.: g) a -> Bool

length :: (f :.: g) a -> Int

elem :: Eq a => a -> (f :.: g) a -> Bool

maximum :: Ord a => (f :.: g) a -> a

minimum :: Ord a => (f :.: g) a -> a

sum :: Num a => (f :.: g) a -> a

product :: Num a => (f :.: g) a -> a

Foldable f => Foldable (M1 i c f)

Since: base-4.9.0.0

Defined in Data.Foldable

Methods

fold :: Monoid m => M1 i c f m -> m

foldMap :: Monoid m => (a -> m) -> M1 i c f a -> m

foldMap' :: Monoid m => (a -> m) -> M1 i c f a -> m

foldr :: (a -> b -> b) -> b -> M1 i c f a -> b

foldr' :: (a -> b -> b) -> b -> M1 i c f a -> b

foldl :: (b -> a -> b) -> b -> M1 i c f a -> b

foldl' :: (b -> a -> b) -> b -> M1 i c f a -> b

foldr1 :: (a -> a -> a) -> M1 i c f a -> a

foldl1 :: (a -> a -> a) -> M1 i c f a -> a

toList :: M1 i c f a -> [a]

null :: M1 i c f a -> Bool

length :: M1 i c f a -> Int

elem :: Eq a => a -> M1 i c f a -> Bool

maximum :: Ord a => M1 i c f a -> a

minimum :: Ord a => M1 i c f a -> a

sum :: Num a => M1 i c f a -> a

product :: Num a => M1 i c f a -> a

concat :: Foldable t => t [a] -> [a]

The concatenation of all the elements of a container of lists.

Examples

Basic usage:

>>> concat (Just [1, 2, 3])
[1,2,3]

>>> concat (Left 42)
[]

>>> concat [[1, 2, 3], [4, 5], [6], []]
[1,2,3,4,5,6]

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.

Examples

Basic usage:

>>> and []
True

>>> and [True]
True

>>> and [False]
False

>>> and [True, True, False]
False

>>> and (False : repeat True) -- Infinite list [False,True,True,True,...
False

>>> and (repeat True)
* Hangs forever *

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.

Examples

Basic usage:

>>> or []
False

>>> or [True]
True

>>> or [False]
False

>>> or [True, True, False]
True

>>> or (True : repeat False) -- Infinite list [True,False,False,False,...
True

>>> or (repeat False)
* Hangs forever *

any :: Foldable t => (a -> Bool) -> t a -> Bool

Determines whether any element of the structure satisfies the predicate.

Examples

Basic usage:

>>> any (> 3) []
False

>>> any (> 3) [1,2]
False

>>> any (> 3) [1,2,3,4,5]
True

>>> any (> 3) [1..]
True

>>> any (> 3) [0, -1..]
* Hangs forever *

all :: Foldable t => (a -> Bool) -> t a -> Bool

Determines whether all elements of the structure satisfy the predicate.

Examples

Basic usage:

>>> all (> 3) []
True

>>> all (> 3) [1,2]
False

>>> all (> 3) [1,2,3,4,5]
False

>>> all (> 3) [1..]
False

>>> all (> 3) [4..]
* Hangs forever *

concatMap :: Foldable t => (a -> [b]) -> t a -> [b]

Map a function over all the elements of a container and concatenate the resulting lists.

Examples

Basic usage:

>>> concatMap (take 3) [[1..], [10..], [100..], [1000..]]
[1,2,3,10,11,12,100,101,102,1000,1001,1002]

>>> concatMap (take 3) (Just [1..])
[1,2,3]

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

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]

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

Map each element of a structure to an Applicative action, evaluate these actions from left to right, and ignore the results. For a version that doesn't ignore the results see traverse.

traverse_ is just like mapM_, but generalised to Applicative actions.

Examples

Basic usage:

>>> traverse_ print ["Hello", "world", "!"]
"Hello"
"world"
"!"

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

for_ is traverse_ with its arguments flipped. For a version that doesn't ignore the results see for. This is forM_ generalised to Applicative actions.

for_ is just like forM_, but generalised to Applicative actions.

Examples

Basic usage:

>>> for_ [1..4] print
1
2
3
4

mapM_ :: (Foldable t, Monad m) => (a -> m b) -> t a -> m ()

Map each element of a structure to a monadic action, evaluate these actions from left to right, and ignore the results. For a version that doesn't ignore the results see mapM.

mapM_ is just like traverse_, but specialised to monadic actions.

forM_ :: (Foldable t, Monad m) => t a -> (a -> m b) -> m ()

forM_ is mapM_ with its arguments flipped. For a version that doesn't ignore the results see forM.

forM_ is just like for_, but specialised to monadic actions.

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

Evaluate each action in the structure from left to right, and ignore the results. For a version that doesn't ignore the results see sequenceA.

sequenceA_ is just like sequence_, but generalised to Applicative actions.

Examples

Basic usage:

>>> sequenceA_ [print "Hello", print "world", print "!"]
"Hello"
"world"
"!"

sequence_ :: (Foldable t, Monad m) => t (m a) -> m ()

Evaluate each monadic action in the structure from left to right, and ignore the results. For a version that doesn't ignore the results see sequence.

sequence_ is just like sequenceA_, but specialised to monadic actions.

asum :: (Foldable t, Alternative f) => t (f a) -> f a

The sum of a collection of actions using (<|>), generalizing concat.

asum is just like msum, but generalised to Alternative.

Examples

Basic usage:

>>> asum [Just "Hello", Nothing, Just "World"]
Just "Hello"

find :: Foldable t => (a -> Bool) -> t a -> Maybe a

The find function takes a predicate and a structure and returns the leftmost element of the structure matching the predicate, or Nothing if there is no such element.

Examples

Basic usage:

>>> find (> 42) [0, 5..]
Just 45

>>> find (> 12) [1..7]
Nothing

class (Functor t, Foldable t) => Traversable (t :: Type -> Type) where

Functors representing data structures that can be transformed to structures of the same shape by performing an Applicative (or, therefore, Monad) action on each element from left to right.

A more detailed description of what same shape means, the various methods, how traversals are constructed, and example advanced use-cases can be found in the Overview section of Data.Traversable.

For the class laws see the Laws section of Data.Traversable.

Minimal complete definition

traverse | sequenceA

Methods

traverse :: Applicative f => (a -> f b) -> t a -> f (t b)

Map each element of a structure to an action, evaluate these actions from left to right, and collect the results. For a version that ignores the results see traverse_.

Examples

Basic usage:

In the first two examples we show each evaluated action mapping to the output structure.

>>> traverse Just [1,2,3,4]
Just [1,2,3,4]

>>> traverse id [Right 1, Right 2, Right 3, Right 4]
Right [1,2,3,4]

In the next examples, we show that Nothing and Left values short circuit the created structure.

>>> traverse (const Nothing) [1,2,3,4]
Nothing

>>> traverse (\x -> if odd x then Just x else Nothing)  [1,2,3,4]
Nothing

>>> traverse id [Right 1, Right 2, Right 3, Right 4, Left 0]
Left 0

sequenceA :: Applicative f => t (f a) -> f (t a)

Evaluate each action in the structure from left to right, and collect the results. For a version that ignores the results see sequenceA_.

Examples

Basic usage:

For the first two examples we show sequenceA fully evaluating a a structure and collecting the results.

>>> sequenceA [Just 1, Just 2, Just 3]
Just [1,2,3]

>>> sequenceA [Right 1, Right 2, Right 3]
Right [1,2,3]

The next two example show Nothing and Just will short circuit the resulting structure if present in the input. For more context, check the Traversable instances for Either and Maybe.

>>> sequenceA [Just 1, Just 2, Just 3, Nothing]
Nothing

>>> sequenceA [Right 1, Right 2, Right 3, Left 4]
Left 4

mapM :: Monad m => (a -> m b) -> t a -> m (t b)

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.

sequence :: Monad m => t (m a) -> m (t a)

Evaluate each monadic action in the structure from left to right, and collect the results. For a version that ignores the results see sequence_.

Examples

Basic usage:

The first two examples are instances where the input and and output of sequence are isomorphic.

>>> sequence $ Right [1,2,3,4]
[Right 1,Right 2,Right 3,Right 4]

>>> sequence $ [Right 1,Right 2,Right 3,Right 4]
Right [1,2,3,4]

The following examples demonstrate short circuit behavior for sequence.

>>> sequence $ Left [1,2,3,4]
Left [1,2,3,4]

>>> sequence $ [Left 0, Right 1,Right 2,Right 3,Right 4]
Left 0

Instances

Traversable ZipList

Since: base-4.9.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> ZipList a -> f (ZipList b)

sequenceA :: Applicative f => ZipList (f a) -> f (ZipList a)

mapM :: Monad m => (a -> m b) -> ZipList a -> m (ZipList b)

sequence :: Monad m => ZipList (m a) -> m (ZipList a)

Traversable Complex

Since: base-4.9.0.0

Defined in Data.Complex

Methods

traverse :: Applicative f => (a -> f b) -> Complex a -> f (Complex b)

sequenceA :: Applicative f => Complex (f a) -> f (Complex a)

mapM :: Monad m => (a -> m b) -> Complex a -> m (Complex b)

sequence :: Monad m => Complex (m a) -> m (Complex a)

Traversable Identity

Since: base-4.9.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> Identity a -> f (Identity b)

sequenceA :: Applicative f => Identity (f a) -> f (Identity a)

mapM :: Monad m => (a -> m b) -> Identity a -> m (Identity b)

sequence :: Monad m => Identity (m a) -> m (Identity a)

Traversable First

Since: base-4.8.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> First a -> f (First b)

sequenceA :: Applicative f => First (f a) -> f (First a)

mapM :: Monad m => (a -> m b) -> First a -> m (First b)

sequence :: Monad m => First (m a) -> m (First a)

Traversable Last

Since: base-4.8.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> Last a -> f (Last b)

sequenceA :: Applicative f => Last (f a) -> f (Last a)

mapM :: Monad m => (a -> m b) -> Last a -> m (Last b)

sequence :: Monad m => Last (m a) -> m (Last a)

Traversable Down

Since: base-4.12.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> Down a -> f (Down b)

sequenceA :: Applicative f => Down (f a) -> f (Down a)

mapM :: Monad m => (a -> m b) -> Down a -> m (Down b)

sequence :: Monad m => Down (m a) -> m (Down a)

Traversable First

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

traverse :: Applicative f => (a -> f b) -> First a -> f (First b)

sequenceA :: Applicative f => First (f a) -> f (First a)

mapM :: Monad m => (a -> m b) -> First a -> m (First b)

sequence :: Monad m => First (m a) -> m (First a)

Traversable Last

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

traverse :: Applicative f => (a -> f b) -> Last a -> f (Last b)

sequenceA :: Applicative f => Last (f a) -> f (Last a)

mapM :: Monad m => (a -> m b) -> Last a -> m (Last b)

sequence :: Monad m => Last (m a) -> m (Last a)

Traversable Max

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

traverse :: Applicative f => (a -> f b) -> Max a -> f (Max b)

sequenceA :: Applicative f => Max (f a) -> f (Max a)

mapM :: Monad m => (a -> m b) -> Max a -> m (Max b)

sequence :: Monad m => Max (m a) -> m (Max a)

Traversable Min

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

traverse :: Applicative f => (a -> f b) -> Min a -> f (Min b)

sequenceA :: Applicative f => Min (f a) -> f (Min a)

mapM :: Monad m => (a -> m b) -> Min a -> m (Min b)

sequence :: Monad m => Min (m a) -> m (Min a)

Traversable Dual

Since: base-4.8.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> Dual a -> f (Dual b)

sequenceA :: Applicative f => Dual (f a) -> f (Dual a)

mapM :: Monad m => (a -> m b) -> Dual a -> m (Dual b)

sequence :: Monad m => Dual (m a) -> m (Dual a)

Traversable Product

Since: base-4.8.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> Product a -> f (Product b)

sequenceA :: Applicative f => Product (f a) -> f (Product a)

mapM :: Monad m => (a -> m b) -> Product a -> m (Product b)

sequence :: Monad m => Product (m a) -> m (Product a)

Traversable Sum

Since: base-4.8.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> Sum a -> f (Sum b)

sequenceA :: Applicative f => Sum (f a) -> f (Sum a)

mapM :: Monad m => (a -> m b) -> Sum a -> m (Sum b)

sequence :: Monad m => Sum (m a) -> m (Sum a)

Traversable NonEmpty

Since: base-4.9.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> NonEmpty a -> f (NonEmpty b)

sequenceA :: Applicative f => NonEmpty (f a) -> f (NonEmpty a)

mapM :: Monad m => (a -> m b) -> NonEmpty a -> m (NonEmpty b)

sequence :: Monad m => NonEmpty (m a) -> m (NonEmpty a)

Traversable Par1

Since: base-4.9.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> Par1 a -> f (Par1 b)

sequenceA :: Applicative f => Par1 (f a) -> f (Par1 a)

mapM :: Monad m => (a -> m b) -> Par1 a -> m (Par1 b)

sequence :: Monad m => Par1 (m a) -> m (Par1 a)

Traversable IntMap

Traverses in order of increasing key.

Defined in Data.IntMap.Internal

Methods

traverse :: Applicative f => (a -> f b) -> IntMap a -> f (IntMap b)

sequenceA :: Applicative f => IntMap (f a) -> f (IntMap a)

mapM :: Monad m => (a -> m b) -> IntMap a -> m (IntMap b)

sequence :: Monad m => IntMap (m a) -> m (IntMap a)

Traversable Digit

Defined in Data.Sequence.Internal

Methods

traverse :: Applicative f => (a -> f b) -> Digit a -> f (Digit b)

sequenceA :: Applicative f => Digit (f a) -> f (Digit a)

mapM :: Monad m => (a -> m b) -> Digit a -> m (Digit b)

sequence :: Monad m => Digit (m a) -> m (Digit a)

Traversable Elem

Defined in Data.Sequence.Internal

Methods

traverse :: Applicative f => (a -> f b) -> Elem a -> f (Elem b)

sequenceA :: Applicative f => Elem (f a) -> f (Elem a)

mapM :: Monad m => (a -> m b) -> Elem a -> m (Elem b)

sequence :: Monad m => Elem (m a) -> m (Elem a)

Traversable FingerTree

Defined in Data.Sequence.Internal

Methods

traverse :: Applicative f => (a -> f b) -> FingerTree a -> f (FingerTree b)

sequenceA :: Applicative f => FingerTree (f a) -> f (FingerTree a)

mapM :: Monad m => (a -> m b) -> FingerTree a -> m (FingerTree b)

sequence :: Monad m => FingerTree (m a) -> m (FingerTree a)

Traversable Node

Defined in Data.Sequence.Internal

Methods

traverse :: Applicative f => (a -> f b) -> Node a -> f (Node b)

sequenceA :: Applicative f => Node (f a) -> f (Node a)

mapM :: Monad m => (a -> m b) -> Node a -> m (Node b)

sequence :: Monad m => Node (m a) -> m (Node a)

Traversable Seq

Defined in Data.Sequence.Internal

Methods

traverse :: Applicative f => (a -> f b) -> Seq a -> f (Seq b)

sequenceA :: Applicative f => Seq (f a) -> f (Seq a)

mapM :: Monad m => (a -> m b) -> Seq a -> m (Seq b)

sequence :: Monad m => Seq (m a) -> m (Seq a)

Traversable ViewL

Defined in Data.Sequence.Internal

Methods

traverse :: Applicative f => (a -> f b) -> ViewL a -> f (ViewL b)

sequenceA :: Applicative f => ViewL (f a) -> f (ViewL a)

mapM :: Monad m => (a -> m b) -> ViewL a -> m (ViewL b)

sequence :: Monad m => ViewL (m a) -> m (ViewL a)

Traversable ViewR

Defined in Data.Sequence.Internal

Methods

traverse :: Applicative f => (a -> f b) -> ViewR a -> f (ViewR b)

sequenceA :: Applicative f => ViewR (f a) -> f (ViewR a)

mapM :: Monad m => (a -> m b) -> ViewR a -> m (ViewR b)

sequence :: Monad m => ViewR (m a) -> m (ViewR a)

Traversable Tree

Defined in Data.Tree

Methods

traverse :: Applicative f => (a -> f b) -> Tree a -> f (Tree b)

sequenceA :: Applicative f => Tree (f a) -> f (Tree a)

mapM :: Monad m => (a -> m b) -> Tree a -> m (Tree b)

sequence :: Monad m => Tree (m a) -> m (Tree a)

Traversable Maybe

Since: base-2.1

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> Maybe a -> f (Maybe b)

sequenceA :: Applicative f => Maybe (f a) -> f (Maybe a)

mapM :: Monad m => (a -> m b) -> Maybe a -> m (Maybe b)

sequence :: Monad m => Maybe (m a) -> m (Maybe a)

Traversable Solo

Since: base-4.15

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> Solo a -> f (Solo b)

sequenceA :: Applicative f => Solo (f a) -> f (Solo a)

mapM :: Monad m => (a -> m b) -> Solo a -> m (Solo b)

sequence :: Monad m => Solo (m a) -> m (Solo a)

Traversable List

Since: base-2.1

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> [a] -> f [b]

sequenceA :: Applicative f => [f a] -> f [a]

mapM :: Monad m => (a -> m b) -> [a] -> m [b]

sequence :: Monad m => [m a] -> m [a]

Traversable (Either a)

Since: base-4.7.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a0 -> f b) -> Either a a0 -> f (Either a b)

sequenceA :: Applicative f => Either a (f a0) -> f (Either a a0)

mapM :: Monad m => (a0 -> m b) -> Either a a0 -> m (Either a b)

sequence :: Monad m => Either a (m a0) -> m (Either a a0)

Traversable (Proxy :: Type -> Type)

Since: base-4.7.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> Proxy a -> f (Proxy b)

sequenceA :: Applicative f => Proxy (f a) -> f (Proxy a)

mapM :: Monad m => (a -> m b) -> Proxy a -> m (Proxy b)

sequence :: Monad m => Proxy (m a) -> m (Proxy a)

Traversable (Arg a)

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

traverse :: Applicative f => (a0 -> f b) -> Arg a a0 -> f (Arg a b)

sequenceA :: Applicative f => Arg a (f a0) -> f (Arg a a0)

mapM :: Monad m => (a0 -> m b) -> Arg a a0 -> m (Arg a b)

sequence :: Monad m => Arg a (m a0) -> m (Arg a a0)

Ix i => Traversable (Array i)

Since: base-2.1

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> Array i a -> f (Array i b)

sequenceA :: Applicative f => Array i (f a) -> f (Array i a)

mapM :: Monad m => (a -> m b) -> Array i a -> m (Array i b)

sequence :: Monad m => Array i (m a) -> m (Array i a)

Traversable (U1 :: Type -> Type)

Since: base-4.9.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> U1 a -> f (U1 b)

sequenceA :: Applicative f => U1 (f a) -> f (U1 a)

mapM :: Monad m => (a -> m b) -> U1 a -> m (U1 b)

sequence :: Monad m => U1 (m a) -> m (U1 a)

Traversable (UAddr :: Type -> Type)

Since: base-4.9.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> UAddr a -> f (UAddr b)

sequenceA :: Applicative f => UAddr (f a) -> f (UAddr a)

mapM :: Monad m => (a -> m b) -> UAddr a -> m (UAddr b)

sequence :: Monad m => UAddr (m a) -> m (UAddr a)

Traversable (UChar :: Type -> Type)

Since: base-4.9.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> UChar a -> f (UChar b)

sequenceA :: Applicative f => UChar (f a) -> f (UChar a)

mapM :: Monad m => (a -> m b) -> UChar a -> m (UChar b)

sequence :: Monad m => UChar (m a) -> m (UChar a)

Traversable (UDouble :: Type -> Type)

Since: base-4.9.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> UDouble a -> f (UDouble b)

sequenceA :: Applicative f => UDouble (f a) -> f (UDouble a)

mapM :: Monad m => (a -> m b) -> UDouble a -> m (UDouble b)

sequence :: Monad m => UDouble (m a) -> m (UDouble a)

Traversable (UFloat :: Type -> Type)

Since: base-4.9.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> UFloat a -> f (UFloat b)

sequenceA :: Applicative f => UFloat (f a) -> f (UFloat a)

mapM :: Monad m => (a -> m b) -> UFloat a -> m (UFloat b)

sequence :: Monad m => UFloat (m a) -> m (UFloat a)

Traversable (UInt :: Type -> Type)

Since: base-4.9.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> UInt a -> f (UInt b)

sequenceA :: Applicative f => UInt (f a) -> f (UInt a)

mapM :: Monad m => (a -> m b) -> UInt a -> m (UInt b)

sequence :: Monad m => UInt (m a) -> m (UInt a)

Traversable (UWord :: Type -> Type)

Since: base-4.9.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> UWord a -> f (UWord b)

sequenceA :: Applicative f => UWord (f a) -> f (UWord a)

mapM :: Monad m => (a -> m b) -> UWord a -> m (UWord b)

sequence :: Monad m => UWord (m a) -> m (UWord a)

Traversable (V1 :: Type -> Type)

Since: base-4.9.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> V1 a -> f (V1 b)

sequenceA :: Applicative f => V1 (f a) -> f (V1 a)

mapM :: Monad m => (a -> m b) -> V1 a -> m (V1 b)

sequence :: Monad m => V1 (m a) -> m (V1 a)

Traversable (Map k)

Traverses in order of increasing key.

Defined in Data.Map.Internal

Methods

traverse :: Applicative f => (a -> f b) -> Map k a -> f (Map k b)

sequenceA :: Applicative f => Map k (f a) -> f (Map k a)

mapM :: Monad m => (a -> m b) -> Map k a -> m (Map k b)

sequence :: Monad m => Map k (m a) -> m (Map k a)

Traversable (HashMap k)

Defined in Data.HashMap.Internal

Methods

traverse :: Applicative f => (a -> f b) -> HashMap k a -> f (HashMap k b)

sequenceA :: Applicative f => HashMap k (f a) -> f (HashMap k a)

mapM :: Monad m => (a -> m b) -> HashMap k a -> m (HashMap k b)

sequence :: Monad m => HashMap k (m a) -> m (HashMap k a)

Traversable f => Traversable (MaybeT f)

Defined in Control.Monad.Trans.Maybe

Methods

traverse :: Applicative f0 => (a -> f0 b) -> MaybeT f a -> f0 (MaybeT f b)

sequenceA :: Applicative f0 => MaybeT f (f0 a) -> f0 (MaybeT f a)

mapM :: Monad m => (a -> m b) -> MaybeT f a -> m (MaybeT f b)

sequence :: Monad m => MaybeT f (m a) -> m (MaybeT f a)

Traversable ((,) a)

Since: base-4.7.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a0 -> f b) -> (a, a0) -> f (a, b)

sequenceA :: Applicative f => (a, f a0) -> f (a, a0)

mapM :: Monad m => (a0 -> m b) -> (a, a0) -> m (a, b)

sequence :: Monad m => (a, m a0) -> m (a, a0)

Traversable (Const m :: Type -> Type)

Since: base-4.7.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> Const m a -> f (Const m b)

sequenceA :: Applicative f => Const m (f a) -> f (Const m a)

mapM :: Monad m0 => (a -> m0 b) -> Const m a -> m0 (Const m b)

sequence :: Monad m0 => Const m (m0 a) -> m0 (Const m a)

Traversable f => Traversable (Ap f)

Since: base-4.12.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f0 => (a -> f0 b) -> Ap f a -> f0 (Ap f b)

sequenceA :: Applicative f0 => Ap f (f0 a) -> f0 (Ap f a)

mapM :: Monad m => (a -> m b) -> Ap f a -> m (Ap f b)

sequence :: Monad m => Ap f (m a) -> m (Ap f a)

Traversable f => Traversable (Alt f)

Since: base-4.12.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f0 => (a -> f0 b) -> Alt f a -> f0 (Alt f b)

sequenceA :: Applicative f0 => Alt f (f0 a) -> f0 (Alt f a)

mapM :: Monad m => (a -> m b) -> Alt f a -> m (Alt f b)

sequence :: Monad m => Alt f (m a) -> m (Alt f a)

Traversable f => Traversable (Rec1 f)

Since: base-4.9.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f0 => (a -> f0 b) -> Rec1 f a -> f0 (Rec1 f b)

sequenceA :: Applicative f0 => Rec1 f (f0 a) -> f0 (Rec1 f a)

mapM :: Monad m => (a -> m b) -> Rec1 f a -> m (Rec1 f b)

sequence :: Monad m => Rec1 f (m a) -> m (Rec1 f a)

Traversable f => Traversable (ExceptT e f)

Defined in Control.Monad.Trans.Except

Methods

traverse :: Applicative f0 => (a -> f0 b) -> ExceptT e f a -> f0 (ExceptT e f b)

sequenceA :: Applicative f0 => ExceptT e f (f0 a) -> f0 (ExceptT e f a)

mapM :: Monad m => (a -> m b) -> ExceptT e f a -> m (ExceptT e f b)

sequence :: Monad m => ExceptT e f (m a) -> m (ExceptT e f a)

Traversable f => Traversable (IdentityT f)

Defined in Control.Monad.Trans.Identity

Methods

traverse :: Applicative f0 => (a -> f0 b) -> IdentityT f a -> f0 (IdentityT f b)

sequenceA :: Applicative f0 => IdentityT f (f0 a) -> f0 (IdentityT f a)

mapM :: Monad m => (a -> m b) -> IdentityT f a -> m (IdentityT f b)

sequence :: Monad m => IdentityT f (m a) -> m (IdentityT f a)

Traversable f => Traversable (WriterT w f)

Defined in Control.Monad.Trans.Writer.Lazy

Methods

traverse :: Applicative f0 => (a -> f0 b) -> WriterT w f a -> f0 (WriterT w f b)

sequenceA :: Applicative f0 => WriterT w f (f0 a) -> f0 (WriterT w f a)

mapM :: Monad m => (a -> m b) -> WriterT w f a -> m (WriterT w f b)

sequence :: Monad m => WriterT w f (m a) -> m (WriterT w f a)

Traversable f => Traversable (WriterT w f)

Defined in Control.Monad.Trans.Writer.Strict

Methods

traverse :: Applicative f0 => (a -> f0 b) -> WriterT w f a -> f0 (WriterT w f b)

sequenceA :: Applicative f0 => WriterT w f (f0 a) -> f0 (WriterT w f a)

mapM :: Monad m => (a -> m b) -> WriterT w f a -> m (WriterT w f b)

sequence :: Monad m => WriterT w f (m a) -> m (WriterT w f a)

(Traversable f, Traversable g) => Traversable (Product f g)

Since: base-4.9.0.0

Defined in Data.Functor.Product

Methods

traverse :: Applicative f0 => (a -> f0 b) -> Product f g a -> f0 (Product f g b)

sequenceA :: Applicative f0 => Product f g (f0 a) -> f0 (Product f g a)

mapM :: Monad m => (a -> m b) -> Product f g a -> m (Product f g b)

sequence :: Monad m => Product f g (m a) -> m (Product f g a)

(Traversable f, Traversable g) => Traversable (Sum f g)

Since: base-4.9.0.0

Defined in Data.Functor.Sum

Methods

traverse :: Applicative f0 => (a -> f0 b) -> Sum f g a -> f0 (Sum f g b)

sequenceA :: Applicative f0 => Sum f g (f0 a) -> f0 (Sum f g a)

mapM :: Monad m => (a -> m b) -> Sum f g a -> m (Sum f g b)

sequence :: Monad m => Sum f g (m a) -> m (Sum f g a)

(Traversable f, Traversable g) => Traversable (f :*: g)

Since: base-4.9.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f0 => (a -> f0 b) -> (f :*: g) a -> f0 ((f :*: g) b)

sequenceA :: Applicative f0 => (f :*: g) (f0 a) -> f0 ((f :*: g) a)

mapM :: Monad m => (a -> m b) -> (f :*: g) a -> m ((f :*: g) b)

sequence :: Monad m => (f :*: g) (m a) -> m ((f :*: g) a)

(Traversable f, Traversable g) => Traversable (f :+: g)

Since: base-4.9.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f0 => (a -> f0 b) -> (f :+: g) a -> f0 ((f :+: g) b)

sequenceA :: Applicative f0 => (f :+: g) (f0 a) -> f0 ((f :+: g) a)

mapM :: Monad m => (a -> m b) -> (f :+: g) a -> m ((f :+: g) b)

sequence :: Monad m => (f :+: g) (m a) -> m ((f :+: g) a)

Traversable (K1 i c :: Type -> Type)

Since: base-4.9.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> K1 i c a -> f (K1 i c b)

sequenceA :: Applicative f => K1 i c (f a) -> f (K1 i c a)

mapM :: Monad m => (a -> m b) -> K1 i c a -> m (K1 i c b)

sequence :: Monad m => K1 i c (m a) -> m (K1 i c a)

(Traversable f, Traversable g) => Traversable (Compose f g)

Since: base-4.9.0.0

Defined in Data.Functor.Compose

Methods

traverse :: Applicative f0 => (a -> f0 b) -> Compose f g a -> f0 (Compose f g b)

sequenceA :: Applicative f0 => Compose f g (f0 a) -> f0 (Compose f g a)

mapM :: Monad m => (a -> m b) -> Compose f g a -> m (Compose f g b)

sequence :: Monad m => Compose f g (m a) -> m (Compose f g a)

(Traversable f, Traversable g) => Traversable (f :.: g)

Since: base-4.9.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f0 => (a -> f0 b) -> (f :.: g) a -> f0 ((f :.: g) b)

sequenceA :: Applicative f0 => (f :.: g) (f0 a) -> f0 ((f :.: g) a)

mapM :: Monad m => (a -> m b) -> (f :.: g) a -> m ((f :.: g) b)

sequence :: Monad m => (f :.: g) (m a) -> m ((f :.: g) a)

Traversable f => Traversable (M1 i c f)

Since: base-4.9.0.0

Defined in Data.Traversable

Methods

traverse :: Applicative f0 => (a -> f0 b) -> M1 i c f a -> f0 (M1 i c f b)

sequenceA :: Applicative f0 => M1 i c f (f0 a) -> f0 (M1 i c f a)

mapM :: Monad m => (a -> m b) -> M1 i c f a -> m (M1 i c f b)

sequence :: Monad m => M1 i c f (m a) -> m (M1 i c f a)

forM :: (Traversable t, Monad m) => t a -> (a -> m b) -> m (t b)

forM is mapM with its arguments flipped. For a version that ignores the results see forM_.

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

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"])

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

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"])

Bi reexports

class Bifoldable (p :: Type -> Type -> Type) where

Bifoldable identifies foldable structures with two different varieties of elements (as opposed to Foldable, which has one variety of element). Common examples are Either and (,):

instance Bifoldable Either where
  bifoldMap f _ (Left  a) = f a
  bifoldMap _ g (Right b) = g b

instance Bifoldable (,) where
  bifoldr f g z (a, b) = f a (g b z)

Some examples below also use the following BiList to showcase empty Bifoldable behaviors when relevant (Either and (,) containing always exactly resp. 1 and 2 elements):

data BiList a b = BiList [a] [b]

instance Bifoldable BiList where
  bifoldr f g z (BiList as bs) = foldr f (foldr g z bs) as

A minimal Bifoldable definition consists of either bifoldMap or bifoldr. When defining more than this minimal set, one should ensure that the following identities hold:

bifold ≡ bifoldMap id id
bifoldMap f g ≡ bifoldr (mappend . f) (mappend . g) mempty
bifoldr f g z t ≡ appEndo (bifoldMap (Endo . f) (Endo . g) t) z

If the type is also a Bifunctor instance, it should satisfy:

bifoldMap f g ≡ bifold . bimap f g

which implies that

bifoldMap f g . bimap h i ≡ bifoldMap (f . h) (g . i)

Since: base-4.10.0.0

Minimal complete definition

bifoldr | bifoldMap

Methods

bifold :: Monoid m => p m m -> m

Combines the elements of a structure using a monoid.

bifold ≡ bifoldMap id id

Examples

Basic usage:

>>> bifold (Right [1, 2, 3])
[1,2,3]

>>> bifold (Left [5, 6])
[5,6]

>>> bifold ([1, 2, 3], [4, 5])
[1,2,3,4,5]

>>> bifold (Product 6, Product 7)
Product {getProduct = 42}

>>> bifold (Sum 6, Sum 7)
Sum {getSum = 13}

Since: base-4.10.0.0

bifoldMap :: Monoid m => (a -> m) -> (b -> m) -> p a b -> m

Combines the elements of a structure, given ways of mapping them to a common monoid.

bifoldMap f g ≡ bifoldr (mappend . f) (mappend . g) mempty

Examples

Basic usage:

>>> bifoldMap (take 3) (fmap digitToInt) ([1..], "89")
[1,2,3,8,9]

>>> bifoldMap (take 3) (fmap digitToInt) (Left [1..])
[1,2,3]

>>> bifoldMap (take 3) (fmap digitToInt) (Right "89")
[8,9]

Since: base-4.10.0.0

bifoldr :: (a -> c -> c) -> (b -> c -> c) -> c -> p a b -> c

Combines the elements of a structure in a right associative manner. Given a hypothetical function toEitherList :: p a b -> [Either a b] yielding a list of all elements of a structure in order, the following would hold:

bifoldr f g z ≡ foldr (either f g) z . toEitherList

Examples

Basic usage:

> bifoldr (+) (*) 3 (5, 7)
26 -- 5 + (7 * 3)

> bifoldr (+) (*) 3 (7, 5)
22 -- 7 + (5 * 3)

> bifoldr (+) (*) 3 (Right 5)
15 -- 5 * 3

> bifoldr (+) (*) 3 (Left 5)
8 -- 5 + 3

Since: base-4.10.0.0

bifoldl :: (c -> a -> c) -> (c -> b -> c) -> c -> p a b -> c

Combines the elements of a structure in a left associative manner. Given a hypothetical function toEitherList :: p a b -> [Either a b] yielding a list of all elements of a structure in order, the following would hold:

bifoldl f g z
     ≡ foldl (acc -> either (f acc) (g acc)) z . toEitherList

Note that if you want an efficient left-fold, you probably want to use bifoldl' instead of bifoldl. The reason is that the latter does not force the "inner" results, resulting in a thunk chain which then must be evaluated from the outside-in.

Examples

Basic usage:

> bifoldl (+) (*) 3 (5, 7)
56 -- (5 + 3) * 7

> bifoldl (+) (*) 3 (7, 5)
50 -- (7 + 3) * 5

> bifoldl (+) (*) 3 (Right 5)
15 -- 5 * 3

> bifoldl (+) (*) 3 (Left 5)
8 -- 5 + 3

Since: base-4.10.0.0

Instances

Bifoldable Either

Since: base-4.10.0.0

Defined in Data.Bifoldable

Methods

bifold :: Monoid m => Either m m -> m

bifoldMap :: Monoid m => (a -> m) -> (b -> m) -> Either a b -> m

bifoldr :: (a -> c -> c) -> (b -> c -> c) -> c -> Either a b -> c

bifoldl :: (c -> a -> c) -> (c -> b -> c) -> c -> Either a b -> c

Bifoldable Arg

Since: base-4.10.0.0

Defined in Data.Semigroup

Methods

bifold :: Monoid m => Arg m m -> m

bifoldMap :: Monoid m => (a -> m) -> (b -> m) -> Arg a b -> m

bifoldr :: (a -> c -> c) -> (b -> c -> c) -> c -> Arg a b -> c

bifoldl :: (c -> a -> c) -> (c -> b -> c) -> c -> Arg a b -> c

Bifoldable Map

Since: containers-0.6.3.1

Defined in Data.Map.Internal

Methods

bifold :: Monoid m => Map m m -> m

bifoldMap :: Monoid m => (a -> m) -> (b -> m) -> Map a b -> m

bifoldr :: (a -> c -> c) -> (b -> c -> c) -> c -> Map a b -> c

bifoldl :: (c -> a -> c) -> (c -> b -> c) -> c -> Map a b -> c

Bifoldable HashMap

Since: unordered-containers-0.2.11

Defined in Data.HashMap.Internal

Methods

bifold :: Monoid m => HashMap m m -> m

bifoldMap :: Monoid m => (a -> m) -> (b -> m) -> HashMap a b -> m

bifoldr :: (a -> c -> c) -> (b -> c -> c) -> c -> HashMap a b -> c

bifoldl :: (c -> a -> c) -> (c -> b -> c) -> c -> HashMap a b -> c

Bifoldable (,)

Since: base-4.10.0.0

Defined in Data.Bifoldable

Methods

bifold :: Monoid m => (m, m) -> m

bifoldMap :: Monoid m => (a -> m) -> (b -> m) -> (a, b) -> m

bifoldr :: (a -> c -> c) -> (b -> c -> c) -> c -> (a, b) -> c

bifoldl :: (c -> a -> c) -> (c -> b -> c) -> c -> (a, b) -> c

Bifoldable (Const :: Type -> Type -> Type)

Since: base-4.10.0.0

Defined in Data.Bifoldable

Methods

bifold :: Monoid m => Const m m -> m

bifoldMap :: Monoid m => (a -> m) -> (b -> m) -> Const a b -> m

bifoldr :: (a -> c -> c) -> (b -> c -> c) -> c -> Const a b -> c

bifoldl :: (c -> a -> c) -> (c -> b -> c) -> c -> Const a b -> c

Bifoldable ((,,) x)

Since: base-4.10.0.0

Defined in Data.Bifoldable

Methods

bifold :: Monoid m => (x, m, m) -> m

bifoldMap :: Monoid m => (a -> m) -> (b -> m) -> (x, a, b) -> m

bifoldr :: (a -> c -> c) -> (b -> c -> c) -> c -> (x, a, b) -> c

bifoldl :: (c -> a -> c) -> (c -> b -> c) -> c -> (x, a, b) -> c

Bifoldable (K1 i :: Type -> Type -> Type)

Since: base-4.10.0.0

Defined in Data.Bifoldable

Methods

bifold :: Monoid m => K1 i m m -> m

bifoldMap :: Monoid m => (a -> m) -> (b -> m) -> K1 i a b -> m

bifoldr :: (a -> c -> c) -> (b -> c -> c) -> c -> K1 i a b -> c

bifoldl :: (c -> a -> c) -> (c -> b -> c) -> c -> K1 i a b -> c

Bifoldable ((,,,) x y)

Since: base-4.10.0.0

Defined in Data.Bifoldable

Methods

bifold :: Monoid m => (x, y, m, m) -> m

bifoldMap :: Monoid m => (a -> m) -> (b -> m) -> (x, y, a, b) -> m

bifoldr :: (a -> c -> c) -> (b -> c -> c) -> c -> (x, y, a, b) -> c

bifoldl :: (c -> a -> c) -> (c -> b -> c) -> c -> (x, y, a, b) -> c

Bifoldable ((,,,,) x y z)

Since: base-4.10.0.0

Defined in Data.Bifoldable

Methods

bifold :: Monoid m => (x, y, z, m, m) -> m

bifoldMap :: Monoid m => (a -> m) -> (b -> m) -> (x, y, z, a, b) -> m

bifoldr :: (a -> c -> c) -> (b -> c -> c) -> c -> (x, y, z, a, b) -> c

bifoldl :: (c -> a -> c) -> (c -> b -> c) -> c -> (x, y, z, a, b) -> c

Bifoldable ((,,,,,) x y z w)

Since: base-4.10.0.0

Defined in Data.Bifoldable

Methods

bifold :: Monoid m => (x, y, z, w, m, m) -> m

bifoldMap :: Monoid m => (a -> m) -> (b -> m) -> (x, y, z, w, a, b) -> m

bifoldr :: (a -> c -> c) -> (b -> c -> c) -> c -> (x, y, z, w, a, b) -> c

bifoldl :: (c -> a -> c) -> (c -> b -> c) -> c -> (x, y, z, w, a, b) -> c

Bifoldable ((,,,,,,) x y z w v)

Since: base-4.10.0.0

Defined in Data.Bifoldable

Methods

bifold :: Monoid m => (x, y, z, w, v, m, m) -> m

bifoldMap :: Monoid m => (a -> m) -> (b -> m) -> (x, y, z, w, v, a, b) -> m

bifoldr :: (a -> c -> c) -> (b -> c -> c) -> c -> (x, y, z, w, v, a, b) -> c

bifoldl :: (c -> a -> c) -> (c -> b -> c) -> c -> (x, y, z, w, v, a, b) -> c

bifoldr' :: Bifoldable t => (a -> c -> c) -> (b -> c -> c) -> c -> t a b -> c

As bifoldr, but strict in the result of the reduction functions at each step.

Since: base-4.10.0.0

bifoldrM :: (Bifoldable t, Monad m) => (a -> c -> m c) -> (b -> c -> m c) -> c -> t a b -> m c

Right associative monadic bifold over a structure.

Since: base-4.10.0.0

bifoldl' :: Bifoldable t => (a -> b -> a) -> (a -> c -> a) -> a -> t b c -> a

As bifoldl, but strict in the result of the reduction functions at each step.

This ensures that each step of the bifold 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, monolithic result (e.g., bilength).

Since: base-4.10.0.0

bifoldlM :: (Bifoldable t, Monad m) => (a -> b -> m a) -> (a -> c -> m a) -> a -> t b c -> m a

Left associative monadic bifold over a structure.

Examples

Basic usage:

>>> bifoldlM (\a b -> print b >> pure a) (\a c -> print (show c) >> pure a) 42 ("Hello", True)
"Hello"
"True"
42

>>> bifoldlM (\a b -> print b >> pure a) (\a c -> print (show c) >> pure a) 42 (Right True)
"True"
42

>>> bifoldlM (\a b -> print b >> pure a) (\a c -> print (show c) >> pure a) 42 (Left "Hello")
"Hello"
42

Since: base-4.10.0.0

bitraverse_ :: (Bifoldable t, Applicative f) => (a -> f c) -> (b -> f d) -> t a b -> f ()

Map each element of a structure using one of two actions, evaluate these actions from left to right, and ignore the results. For a version that doesn't ignore the results, see bitraverse.

Examples

Basic usage:

>>> bitraverse_ print (print . show) ("Hello", True)
"Hello"
"True"

>>> bitraverse_ print (print . show) (Right True)
"True"

>>> bitraverse_ print (print . show) (Left "Hello")
"Hello"

Since: base-4.10.0.0

bifor_ :: (Bifoldable t, Applicative f) => t a b -> (a -> f c) -> (b -> f d) -> f ()

As bitraverse_, but with the structure as the primary argument. For a version that doesn't ignore the results, see bifor.

Examples

Basic usage:

>>> bifor_ ("Hello", True) print (print . show)
"Hello"
"True"

>>> bifor_ (Right True) print (print . show)
"True"

>>> bifor_ (Left "Hello") print (print . show)
"Hello"

Since: base-4.10.0.0

bisequence_ :: (Bifoldable t, Applicative f) => t (f a) (f b) -> f ()

Evaluate each action in the structure from left to right, and ignore the results. For a version that doesn't ignore the results, see bisequence.

Examples

Basic usage:

>>> bisequence_ (print "Hello", print "World")
"Hello"
"World"

>>> bisequence_ (Left (print "Hello"))
"Hello"

>>> bisequence_ (Right (print "World"))
"World"

Since: base-4.10.0.0

biasum :: (Bifoldable t, Alternative f) => t (f a) (f a) -> f a

The sum of a collection of actions, generalizing biconcat.

Examples

Basic usage:

>>> biasum (Nothing, Nothing)
Nothing

>>> biasum (Nothing, Just 42)
Just 42

>>> biasum (Just 18, Nothing)
Just 18

>>> biasum (Just 18, Just 42)
Just 18

Since: base-4.10.0.0

biList :: Bifoldable t => t a a -> [a]

Collects the list of elements of a structure, from left to right.

Examples

Basic usage:

>>> biList (18, 42)
[18,42]

>>> biList (Left 18)
[18]

Since: base-4.10.0.0

binull :: Bifoldable t => t a b -> Bool

Test whether the structure is empty.

Examples

Basic usage:

>>> binull (18, 42)
False

>>> binull (Right 42)
False

>>> binull (BiList [] [])
True

Since: base-4.10.0.0

bilength :: Bifoldable t => t a b -> Int

Returns the size/length of a finite structure as an Int.

Examples

Basic usage:

>>> bilength (True, 42)
2

>>> bilength (Right 42)
1

>>> bilength (BiList [1,2,3] [4,5])
5

>>> bilength (BiList [] [])
0

On infinite structures, this function hangs:

> bilength (BiList [1..] [])
* Hangs forever *

Since: base-4.10.0.0

bielem :: (Bifoldable t, Eq a) => a -> t a a -> Bool

Does the element occur in the structure?

Examples

Basic usage:

>>> bielem 42 (17, 42)
True

>>> bielem 42 (17, 43)
False

>>> bielem 42 (Left 42)
True

>>> bielem 42 (Right 13)
False

>>> bielem 42 (BiList [1..5] [1..100])
True

>>> bielem 42 (BiList [1..5] [1..41])
False

Since: base-4.10.0.0

biand :: Bifoldable t => t Bool Bool -> Bool

biand 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.

Examples

Basic usage:

>>> biand (True, False)
False

>>> biand (True, True)
True

>>> biand (Left True)
True

Empty structures yield True:

>>> biand (BiList [] [])
True

A False value finitely far from the left end yields False (short circuit):

>>> biand (BiList [True, True, False, True] (repeat True))
False

A False value infinitely far from the left end hangs:

> biand (BiList (repeat True) [False])
* Hangs forever *

An infinitely True value hangs:

> biand (BiList (repeat True) [])
* Hangs forever *

Since: base-4.10.0.0

bior :: Bifoldable t => t Bool Bool -> Bool

bior 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.

Examples

Basic usage:

>>> bior (True, False)
True

>>> bior (False, False)
False

>>> bior (Left True)
True

Empty structures yield False:

>>> bior (BiList [] [])
False

A True value finitely far from the left end yields True (short circuit):

>>> bior (BiList [False, False, True, False] (repeat False))
True

A True value infinitely far from the left end hangs:

> bior (BiList (repeat False) [True])
* Hangs forever *

An infinitely False value hangs:

> bior (BiList (repeat False) [])
* Hangs forever *

Since: base-4.10.0.0

biany :: Bifoldable t => (a -> Bool) -> (b -> Bool) -> t a b -> Bool

Determines whether any element of the structure satisfies its appropriate predicate argument. Empty structures yield False.

Examples

Basic usage:

>>> biany even isDigit (27, 't')
False

>>> biany even isDigit (27, '8')
True

>>> biany even isDigit (26, 't')
True

>>> biany even isDigit (Left 27)
False

>>> biany even isDigit (Left 26)
True

>>> biany even isDigit (BiList [27, 53] ['t', '8'])
True

Empty structures yield False:

>>> biany even isDigit (BiList [] [])
False

Since: base-4.10.0.0

biall :: Bifoldable t => (a -> Bool) -> (b -> Bool) -> t a b -> Bool

Determines whether all elements of the structure satisfy their appropriate predicate argument. Empty structures yield True.

Examples

Basic usage:

>>> biall even isDigit (27, 't')
False

>>> biall even isDigit (26, '8')
True

>>> biall even isDigit (Left 27)
False

>>> biall even isDigit (Left 26)
True

>>> biall even isDigit (BiList [26, 52] ['3', '8'])
True

Empty structures yield True:

>>> biall even isDigit (BiList [] [])
True

Since: base-4.10.0.0

bifind :: Bifoldable t => (a -> Bool) -> t a a -> Maybe a

The bifind function takes a predicate and a structure and returns the leftmost element of the structure matching the predicate, or Nothing if there is no such element.

Examples

Basic usage:

>>> bifind even (27, 53)
Nothing

>>> bifind even (27, 52)
Just 52

>>> bifind even (26, 52)
Just 26

Empty structures always yield Nothing:

>>> bifind even (BiList [] [])
Nothing

Since: base-4.10.0.0

class (Bifunctor t, Bifoldable t) => Bitraversable (t :: Type -> Type -> Type) where

Bitraversable identifies bifunctorial data structures whose elements can be traversed in order, performing Applicative or Monad actions at each element, and collecting a result structure with the same shape.

As opposed to Traversable data structures, which have one variety of element on which an action can be performed, Bitraversable data structures have two such varieties of elements.

A definition of bitraverse must satisfy the following laws:

Naturality

bitraverse (t . f) (t . g) ≡ t . bitraverse f g for every applicative transformation t

Identity

bitraverse Identity Identity ≡ Identity

Composition

Compose . fmap (bitraverse g1 g2) . bitraverse f1 f2 ≡ bitraverse (Compose . fmap g1 . f1) (Compose . fmap g2 . f2)

where an applicative transformation is a function

t :: (Applicative f, Applicative g) => f a -> g a

preserving the Applicative operations:

t (pure x) = pure x
t (f <*> x) = t f <*> t x

and the identity functor Identity and composition functors Compose are from Data.Functor.Identity and Data.Functor.Compose.

Some simple examples are Either and (,):

instance Bitraversable Either where
  bitraverse f _ (Left x) = Left <$> f x
  bitraverse _ g (Right y) = Right <$> g y

instance Bitraversable (,) where
  bitraverse f g (x, y) = (,) <$> f x <*> g y

Bitraversable relates to its superclasses in the following ways:

bimap f g ≡ runIdentity . bitraverse (Identity . f) (Identity . g)
bifoldMap f g = getConst . bitraverse (Const . f) (Const . g)

These are available as bimapDefault and bifoldMapDefault respectively.

Since: base-4.10.0.0

Methods

bitraverse :: Applicative f => (a -> f c) -> (b -> f d) -> t a b -> f (t c d)

Evaluates the relevant functions at each element in the structure, running the action, and builds a new structure with the same shape, using the results produced from sequencing the actions.

bitraverse f g ≡ bisequenceA . bimap f g

For a version that ignores the results, see bitraverse_.

Examples

Basic usage:

>>> bitraverse listToMaybe (find odd) (Left [])
Nothing

>>> bitraverse listToMaybe (find odd) (Left [1, 2, 3])
Just (Left 1)

>>> bitraverse listToMaybe (find odd) (Right [4, 5])
Just (Right 5)

>>> bitraverse listToMaybe (find odd) ([1, 2, 3], [4, 5])
Just (1,5)

>>> bitraverse listToMaybe (find odd) ([], [4, 5])
Nothing

Since: base-4.10.0.0

Instances

Bitraversable Either

Since: base-4.10.0.0

Defined in Data.Bitraversable

Methods

bitraverse :: Applicative f => (a -> f c) -> (b -> f d) -> Either a b -> f (Either c d)

Bitraversable Arg

Since: base-4.10.0.0

Defined in Data.Semigroup

Methods

bitraverse :: Applicative f => (a -> f c) -> (b -> f d) -> Arg a b -> f (Arg c d)

Bitraversable (,)

Since: base-4.10.0.0

Defined in Data.Bitraversable

Methods

bitraverse :: Applicative f => (a -> f c) -> (b -> f d) -> (a, b) -> f (c, d)

Bitraversable (Const :: Type -> Type -> Type)

Since: base-4.10.0.0

Defined in Data.Bitraversable

Methods

bitraverse :: Applicative f => (a -> f c) -> (b -> f d) -> Const a b -> f (Const c d)

Bitraversable ((,,) x)

Since: base-4.10.0.0

Defined in Data.Bitraversable

Methods

bitraverse :: Applicative f => (a -> f c) -> (b -> f d) -> (x, a, b) -> f (x, c, d)

Bitraversable (K1 i :: Type -> Type -> Type)

Since: base-4.10.0.0

Defined in Data.Bitraversable

Methods

bitraverse :: Applicative f => (a -> f c) -> (b -> f d) -> K1 i a b -> f (K1 i c d)

Bitraversable ((,,,) x y)

Since: base-4.10.0.0

Defined in Data.Bitraversable

Methods

bitraverse :: Applicative f => (a -> f c) -> (b -> f d) -> (x, y, a, b) -> f (x, y, c, d)

Bitraversable ((,,,,) x y z)

Since: base-4.10.0.0

Defined in Data.Bitraversable

Methods

bitraverse :: Applicative f => (a -> f c) -> (b -> f d) -> (x, y, z, a, b) -> f (x, y, z, c, d)

Bitraversable ((,,,,,) x y z w)

Since: base-4.10.0.0

Defined in Data.Bitraversable

Methods

bitraverse :: Applicative f => (a -> f c) -> (b -> f d) -> (x, y, z, w, a, b) -> f (x, y, z, w, c, d)

Bitraversable ((,,,,,,) x y z w v)

Since: base-4.10.0.0

Defined in Data.Bitraversable

Methods

bitraverse :: Applicative f => (a -> f c) -> (b -> f d) -> (x, y, z, w, v, a, b) -> f (x, y, z, w, v, c, d)

bifor :: (Bitraversable t, Applicative f) => t a b -> (a -> f c) -> (b -> f d) -> f (t c d)

bifor is bitraverse with the structure as the first argument. For a version that ignores the results, see bifor_.

Examples

Basic usage:

>>> bifor (Left []) listToMaybe (find even)
Nothing

>>> bifor (Left [1, 2, 3]) listToMaybe (find even)
Just (Left 1)

>>> bifor (Right [4, 5]) listToMaybe (find even)
Just (Right 4)

>>> bifor ([1, 2, 3], [4, 5]) listToMaybe (find even)
Just (1,4)

>>> bifor ([], [4, 5]) listToMaybe (find even)
Nothing

Since: base-4.10.0.0

bisequence :: (Bitraversable t, Applicative f) => t (f a) (f b) -> f (t a b)

Sequences all the actions in a structure, building a new structure with the same shape using the results of the actions. For a version that ignores the results, see bisequence_.

bisequence ≡ bitraverse id id

Examples

Basic usage:

>>> bisequence (Just 4, Nothing)
Nothing

>>> bisequence (Just 4, Just 5)
Just (4,5)

>>> bisequence ([1, 2, 3], [4, 5])
[(1,4),(1,5),(2,4),(2,5),(3,4),(3,5)]

Since: base-4.10.0.0

bimapDefault :: Bitraversable t => (a -> b) -> (c -> d) -> t a c -> t b d

A default definition of bimap in terms of the Bitraversable operations.

bimapDefault f g ≡
     runIdentity . bitraverse (Identity . f) (Identity . g)

Since: base-4.10.0.0

bifoldMapDefault :: (Bitraversable t, Monoid m) => (a -> m) -> (b -> m) -> t a b -> m

A default definition of bifoldMap in terms of the Bitraversable operations.

bifoldMapDefault f g ≡
    getConst . bitraverse (Const . f) (Const . g)

Since: base-4.10.0.0