Foldable overview

Added in v2.0.0

Table of contents

model

Foldable (interface)

Signature

export interface Foldable<F> {
  readonly URI: F
  readonly reduce: <A, B>(fa: HKT<F, A>, b: B, f: (b: B, a: A) => B) => B
  readonly foldMap: <M>(M: Monoid<M>) => <A>(fa: HKT<F, A>, f: (a: A) => M) => M
  readonly reduceRight: <A, B>(fa: HKT<F, A>, b: B, f: (a: A, b: B) => B) => B
}

Added in v2.0.0

Foldable1 (interface)

Signature

export interface Foldable1<F extends URIS> {
  readonly URI: F
  readonly reduce: <A, B>(fa: Kind<F, A>, b: B, f: (b: B, a: A) => B) => B
  readonly foldMap: <M>(M: Monoid<M>) => <A>(fa: Kind<F, A>, f: (a: A) => M) => M
  readonly reduceRight: <A, B>(fa: Kind<F, A>, b: B, f: (a: A, b: B) => B) => B
}

Added in v2.0.0

Foldable2 (interface)

Signature

export interface Foldable2<F extends URIS2> {
  readonly URI: F
  readonly reduce: <E, A, B>(fa: Kind2<F, E, A>, b: B, f: (b: B, a: A) => B) => B
  readonly foldMap: <M>(M: Monoid<M>) => <E, A>(fa: Kind2<F, E, A>, f: (a: A) => M) => M
  readonly reduceRight: <E, A, B>(fa: Kind2<F, E, A>, b: B, f: (a: A, b: B) => B) => B
}

Added in v2.0.0

Foldable2C (interface)

Signature

export interface Foldable2C<F extends URIS2, E> {
  readonly URI: F
  readonly _E: E
  readonly reduce: <A, B>(fa: Kind2<F, E, A>, b: B, f: (b: B, a: A) => B) => B
  readonly foldMap: <M>(M: Monoid<M>) => <A>(fa: Kind2<F, E, A>, f: (a: A) => M) => M
  readonly reduceRight: <A, B>(fa: Kind2<F, E, A>, b: B, f: (a: A, b: B) => B) => B
}

Added in v2.0.0

Foldable3 (interface)

Signature

export interface Foldable3<F extends URIS3> {
  readonly URI: F
  readonly reduce: <R, E, A, B>(fa: Kind3<F, R, E, A>, b: B, f: (b: B, a: A) => B) => B
  readonly foldMap: <M>(M: Monoid<M>) => <R, E, A>(fa: Kind3<F, R, E, A>, f: (a: A) => M) => M
  readonly reduceRight: <R, E, A, B>(fa: Kind3<F, R, E, A>, b: B, f: (a: A, b: B) => B) => B
}

Added in v2.0.0

Foldable3C (interface)

Signature

export interface Foldable3C<F extends URIS3, E> {
  readonly URI: F
  readonly _E: E
  readonly reduce: <R, A, B>(fa: Kind3<F, R, E, A>, b: B, f: (b: B, a: A) => B) => B
  readonly foldMap: <M>(M: Monoid<M>) => <R, A>(fa: Kind3<F, R, E, A>, f: (a: A) => M) => M
  readonly reduceRight: <R, A, B>(fa: Kind3<F, R, E, A>, b: B, f: (a: A, b: B) => B) => B
}

Added in v2.2.0

Foldable4 (interface)

Signature

export interface Foldable4<F extends URIS4> {
  readonly URI: F
  readonly reduce: <S, R, E, A, B>(fa: Kind4<F, S, R, E, A>, b: B, f: (b: B, a: A) => B) => B
  readonly foldMap: <M>(M: Monoid<M>) => <S, R, E, A>(fa: Kind4<F, S, R, E, A>, f: (a: A) => M) => M
  readonly reduceRight: <S, R, E, A, B>(fa: Kind4<F, S, R, E, A>, b: B, f: (a: A, b: B) => B) => B
}

Added in v2.0.0

utils

foldMap

foldMap composition.

Signature

export declare function foldMap<F extends URIS, G extends URIS>(
  F: Foldable1<F>,
  G: Foldable1<G>
): <M>(M: Monoid<M>) => <A>(f: (a: A) => M) => (fga: Kind<F, Kind<G, A>>) => M
export declare function foldMap<F, G>(
  F: Foldable<F>,
  G: Foldable<G>
): <M>(M: Monoid<M>) => <A>(f: (a: A) => M) => (fga: HKT<F, HKT<G, A>>) => M

Added in v2.10.0

intercalate

Fold a data structure, accumulating values in some Monoid, combining adjacent elements using the specified separator

Signature

export declare function intercalate<M, F extends URIS3>(
  M: Monoid<M>,
  F: Foldable3<F>
): <R, E>(middle: M, fm: Kind3<F, R, E, M>) => M
export declare function intercalate<M, F extends URIS2>(
  M: Monoid<M>,
  F: Foldable2<F>
): <E>(middle: M, fm: Kind2<F, E, M>) => M
export declare function intercalate<M, F extends URIS2, E>(
  M: Monoid<M>,
  F: Foldable2C<F, E>
): (middle: M, fm: Kind2<F, E, M>) => M
export declare function intercalate<M, F extends URIS>(M: Monoid<M>, F: Foldable1<F>): (middle: M, fm: Kind<F, M>) => M
export declare function intercalate<M, F>(M: Monoid<M>, F: Foldable<F>): (middle: M, fm: HKT<F, M>) => M

Example

import { intercalate } from 'fp-ts/Foldable'
import * as S from 'fp-ts/string'
import { make, Foldable } from 'fp-ts/Tree'

const t = make('a', [make('b', []), make('c', []), make('d', [])])
assert.strictEqual(intercalate(S.Monoid, Foldable)('|', t), 'a|b|c|d')

Added in v2.0.0

reduce

reduce composition.

Signature

export declare function reduce<F extends URIS, G extends URIS>(
  F: Foldable1<F>,
  G: Foldable1<G>
): <B, A>(b: B, f: (b: B, a: A) => B) => (fga: Kind<F, Kind<G, A>>) => B
export declare function reduce<F, G>(
  F: Foldable<F>,
  G: Foldable<G>
): <B, A>(b: B, f: (b: B, a: A) => B) => (fga: HKT<F, HKT<G, A>>) => B

Added in v2.10.0

reduceM

Similar to ‘reduce’, but the result is encapsulated in a monad.

Note: this function is not generally stack-safe, e.g., for monads which build up thunks a la IO.

Signature

export declare function reduceM<M extends URIS3, F extends URIS>(
  M: Monad3<M>,
  F: Foldable1<F>
): <B, A, R, E>(b: B, f: (b: B, a: A) => Kind3<M, R, E, B>) => (fa: Kind<F, A>) => Kind3<M, R, E, B>
export declare function reduceM<M extends URIS3, F extends URIS, E>(
  M: Monad3C<M, E>,
  F: Foldable1<F>
): <B, A, R>(b: B, f: (b: B, a: A) => Kind3<M, R, E, B>) => (fa: Kind<F, A>) => Kind3<M, R, E, B>
export declare function reduceM<M extends URIS2, F extends URIS>(
  M: Monad2<M>,
  F: Foldable1<F>
): <B, A, E>(b: B, f: (b: B, a: A) => Kind2<M, E, B>) => (fa: Kind<F, A>) => Kind2<M, E, B>
export declare function reduceM<M extends URIS2, F extends URIS, E>(
  M: Monad2C<M, E>,
  F: Foldable1<F>
): <B, A>(b: B, f: (b: B, a: A) => Kind2<M, E, B>) => (fa: Kind<F, A>) => Kind2<M, E, B>
export declare function reduceM<M extends URIS, F extends URIS>(
  M: Monad1<M>,
  F: Foldable1<F>
): <B, A>(b: B, f: (b: B, a: A) => Kind<M, B>) => (fa: Kind<F, A>) => Kind<M, B>
export declare function reduceM<M, F>(
  M: Monad<M>,
  F: Foldable<F>
): <B, A>(b: B, f: (b: B, a: A) => HKT<M, B>) => (fa: HKT<F, A>) => HKT<M, B>

Example

import { reduceM } from 'fp-ts/Foldable'
import { Monad, some } from 'fp-ts/Option'
import { make, Foldable } from 'fp-ts/Tree'
import { pipe } from 'fp-ts/function'

const t = make(1, [make(2, []), make(3, []), make(4, [])])
assert.deepStrictEqual(
  pipe(
    t,
    reduceM(Monad, Foldable)(0, (b, a) => (a > 2 ? some(b + a) : some(b)))
  ),
  some(7)
)

Added in v2.8.0

reduceRight

reduceRight composition.

Signature

export declare function reduceRight<F extends URIS, G extends URIS>(
  F: Foldable1<F>,
  G: Foldable1<G>
): <B, A>(b: B, f: (a: A, b: B) => B) => (fga: Kind<F, Kind<G, A>>) => B
export declare function reduceRight<F, G>(
  F: Foldable<F>,
  G: Foldable<G>
): <B, A>(b: B, f: (a: A, b: B) => B) => (fga: HKT<F, HKT<G, A>>) => B

Added in v2.10.0

toReadonlyArray

Transforms a Foldable into a toReadonlyArray.

Signature

export declare function toReadonlyArray<F extends URIS4>(
  F: Foldable4<F>
): <S, R, E, A>(fa: Kind4<F, S, R, E, A>) => ReadonlyArray<A>
export declare function toReadonlyArray<F extends URIS3>(
  F: Foldable3<F>
): <R, E, A>(fa: Kind3<F, R, E, A>) => ReadonlyArray<A>
export declare function toReadonlyArray<F extends URIS3, E>(
  F: Foldable3C<F, E>
): <R, A>(fa: Kind3<F, R, E, A>) => ReadonlyArray<A>
export declare function toReadonlyArray<F extends URIS2>(
  F: Foldable2<F>
): <E, A>(fa: Kind2<F, E, A>) => ReadonlyArray<A>
export declare function toReadonlyArray<F extends URIS2, E>(
  F: Foldable2C<F, E>
): <A>(fa: Kind2<F, E, A>) => ReadonlyArray<A>
export declare function toReadonlyArray<F extends URIS>(F: Foldable1<F>): <A>(fa: Kind<F, A>) => ReadonlyArray<A>
export declare function toReadonlyArray<F>(F: Foldable<F>): <A>(fa: HKT<F, A>) => ReadonlyArray<A>

Example

import { toReadonlyArray } from 'fp-ts/Foldable'
import { Foldable, make } from 'fp-ts/Tree'

const t = make(1, [make(2, []), make(3, []), make(4, [])])
assert.deepStrictEqual(toReadonlyArray(Foldable)(t), [1, 2, 3, 4])

Added in v2.10.0

traverse_

Traverse a data structure, performing some effects encoded by an Applicative functor at each value, ignoring the final result.

Signature

export declare function traverse_<M extends URIS3, F extends URIS>(
  M: Applicative3<M>,
  F: Foldable1<F>
): <R, E, A, B>(fa: Kind<F, A>, f: (a: A) => Kind3<M, R, E, B>) => Kind3<M, R, E, void>
export declare function traverse_<M extends URIS2, F extends URIS>(
  M: Applicative2<M>,
  F: Foldable1<F>
): <E, A, B>(fa: Kind<F, A>, f: (a: A) => Kind2<M, E, B>) => Kind2<M, E, void>
export declare function traverse_<M extends URIS2, F extends URIS, E>(
  M: Applicative2C<M, E>,
  F: Foldable1<F>
): <A, B>(fa: Kind<F, A>, f: (a: A) => Kind2<M, E, B>) => Kind2<M, E, void>
export declare function traverse_<M extends URIS, F extends URIS>(
  M: Applicative1<M>,
  F: Foldable1<F>
): <A, B>(fa: Kind<F, A>, f: (a: A) => Kind<M, B>) => Kind<M, void>
export declare function traverse_<M, F>(
  M: Applicative<M>,
  F: Foldable<F>
): <A, B>(fa: HKT<F, A>, f: (a: A) => HKT<M, B>) => HKT<M, void>

Example

import { Foldable } from 'fp-ts/Array'
import { traverse_ } from 'fp-ts/Foldable'
import { Applicative } from 'fp-ts/IO'

let log = ''
const append = (s: string) => () => (log += s)
traverse_(Applicative, Foldable)(['a', 'b', 'c'], append)()
assert.strictEqual(log, 'abc')

Added in v2.0.0

zone of death

FoldableComposition11 (interface)

Signature

export interface FoldableComposition11<F extends URIS, G extends URIS> {
  readonly reduce: <A, B>(fga: Kind<F, Kind<G, A>>, b: B, f: (b: B, a: A) => B) => B
  readonly foldMap: <M>(M: Monoid<M>) => <A>(fa: Kind<F, Kind<G, A>>, f: (a: A) => M) => M
  readonly reduceRight: <A, B>(fa: Kind<F, Kind<G, A>>, b: B, f: (a: A, b: B) => B) => B
}

Added in v2.0.0

FoldableComposition12C (interface)

Signature

export interface FoldableComposition12C<F extends URIS, G extends URIS2, E> {
  readonly reduce: <A, B>(fga: Kind<F, Kind2<G, E, A>>, b: B, f: (b: B, a: A) => B) => B
  readonly foldMap: <M>(M: Monoid<M>) => <A>(fa: Kind<F, Kind2<G, E, A>>, f: (a: A) => M) => M
  readonly reduceRight: <A, B>(fa: Kind<F, Kind2<G, E, A>>, b: B, f: (a: A, b: B) => B) => B
}

Added in v2.0.0

FoldableComposition12 (interface)

Signature

export interface FoldableComposition12<F extends URIS, G extends URIS2> {
  readonly reduce: <E, A, B>(fga: Kind<F, Kind2<G, E, A>>, b: B, f: (b: B, a: A) => B) => B
  readonly foldMap: <M>(M: Monoid<M>) => <E, A>(fa: Kind<F, Kind2<G, E, A>>, f: (a: A) => M) => M
  readonly reduceRight: <E, A, B>(fa: Kind<F, Kind2<G, E, A>>, b: B, f: (a: A, b: B) => B) => B
}

Added in v2.0.0

FoldableComposition21 (interface)

Signature

export interface FoldableComposition21<F extends URIS2, G extends URIS> {
  readonly reduce: <E, A, B>(fga: Kind2<F, E, Kind<G, A>>, b: B, f: (b: B, a: A) => B) => B
  readonly foldMap: <M>(M: Monoid<M>) => <E, A>(fa: Kind2<F, E, Kind<G, A>>, f: (a: A) => M) => M
  readonly reduceRight: <E, A, B>(fa: Kind2<F, E, Kind<G, A>>, b: B, f: (a: A, b: B) => B) => B
}

Added in v2.0.0

FoldableComposition22C (interface)

Signature

export interface FoldableComposition22C<F extends URIS2, G extends URIS2, E> {
  readonly reduce: <FE, A, B>(fga: Kind2<F, FE, Kind2<G, E, A>>, b: B, f: (b: B, a: A) => B) => B
  readonly foldMap: <M>(M: Monoid<M>) => <FE, A>(fa: Kind2<F, FE, Kind2<G, E, A>>, f: (a: A) => M) => M
  readonly reduceRight: <FE, A, B>(fa: Kind2<F, FE, Kind2<G, E, A>>, b: B, f: (a: A, b: B) => B) => B
}

Added in v2.0.0

FoldableComposition22 (interface)

Signature

export interface FoldableComposition22<F extends URIS2, G extends URIS2> {
  readonly reduce: <FE, GE, A, B>(fga: Kind2<F, FE, Kind2<G, GE, A>>, b: B, f: (b: B, a: A) => B) => B
  readonly foldMap: <M>(M: Monoid<M>) => <FE, GE, A>(fa: Kind2<F, FE, Kind2<G, GE, A>>, f: (a: A) => M) => M
  readonly reduceRight: <FE, GE, A, B>(fa: Kind2<F, FE, Kind2<G, GE, A>>, b: B, f: (a: A, b: B) => B) => B
}

Added in v2.0.0

FoldableComposition2C1 (interface)

Signature

export interface FoldableComposition2C1<F extends URIS2, G extends URIS, E> {
  readonly reduce: <A, B>(fga: Kind2<F, E, Kind<G, A>>, b: B, f: (b: B, a: A) => B) => B
  readonly foldMap: <M>(M: Monoid<M>) => <A>(fa: Kind2<F, E, Kind<G, A>>, f: (a: A) => M) => M
  readonly reduceRight: <A, B>(fa: Kind2<F, E, Kind<G, A>>, b: B, f: (a: A, b: B) => B) => B
}

Added in v2.0.0

FoldableComposition (interface)

Signature

export interface FoldableComposition<F, G> {
  readonly reduce: <A, B>(fga: HKT<F, HKT<G, A>>, b: B, f: (b: B, a: A) => B) => B
  readonly foldMap: <M>(M: Monoid<M>) => <A>(fa: HKT<F, HKT<G, A>>, f: (a: A) => M) => M
  readonly reduceRight: <A, B>(fa: HKT<F, HKT<G, A>>, b: B, f: (a: A, b: B) => B) => B
}

Added in v2.0.0

foldM

Use reduceM instead

Signature

export declare function foldM<M extends URIS3, F extends URIS>(
  M: Monad3<M>,
  F: Foldable1<F>
): <R, E, A, B>(fa: Kind<F, A>, b: B, f: (b: B, a: A) => Kind3<M, R, E, B>) => Kind3<M, R, E, B>
export declare function foldM<M extends URIS3, F extends URIS, E>(
  M: Monad3C<M, E>,
  F: Foldable1<F>
): <R, A, B>(fa: Kind<F, A>, b: B, f: (b: B, a: A) => Kind3<M, R, E, B>) => Kind3<M, R, E, B>
export declare function foldM<M extends URIS2, F extends URIS>(
  M: Monad2<M>,
  F: Foldable1<F>
): <E, A, B>(fa: Kind<F, A>, b: B, f: (b: B, a: A) => Kind2<M, E, B>) => Kind2<M, E, B>
export declare function foldM<M extends URIS2, F extends URIS, E>(
  M: Monad2C<M, E>,
  F: Foldable1<F>
): <A, B>(fa: Kind<F, A>, b: B, f: (b: B, a: A) => Kind2<M, E, B>) => Kind2<M, E, B>
export declare function foldM<M extends URIS, F extends URIS>(
  M: Monad1<M>,
  F: Foldable1<F>
): <A, B>(fa: Kind<F, A>, b: B, f: (b: B, a: A) => Kind<M, B>) => Kind<M, B>
export declare function foldM<M, F>(
  M: Monad<M>,
  F: Foldable<F>
): <A, B>(fa: HKT<F, A>, b: B, f: (b: B, a: A) => HKT<M, B>) => HKT<M, B>

Added in v2.0.0

getFoldableComposition

Use

instead.

Signature

export declare function getFoldableComposition<F extends URIS2, G extends URIS2, E>(
  F: Foldable2<F>,
  G: Foldable2C<G, E>
): FoldableComposition22C<F, G, E>
export declare function getFoldableComposition<F extends URIS2, G extends URIS2>(
  F: Foldable2<F>,
  G: Foldable2<G>
): FoldableComposition22<F, G>
export declare function getFoldableComposition<F extends URIS2, G extends URIS, E>(
  F: Foldable2C<F, E>,
  G: Foldable1<G>
): FoldableComposition2C1<F, G, E>
export declare function getFoldableComposition<F extends URIS2, G extends URIS>(
  F: Foldable2<F>,
  G: Foldable1<G>
): FoldableComposition21<F, G>
export declare function getFoldableComposition<F extends URIS, G extends URIS2, E>(
  F: Foldable1<F>,
  G: Foldable2C<G, E>
): FoldableComposition12C<F, G, E>
export declare function getFoldableComposition<F extends URIS, G extends URIS2>(
  F: Foldable1<F>,
  G: Foldable2<G>
): FoldableComposition12<F, G>
export declare function getFoldableComposition<F extends URIS, G extends URIS>(
  F: Foldable1<F>,
  G: Foldable1<G>
): FoldableComposition11<F, G>
export declare function getFoldableComposition<F, G>(F: Foldable<F>, G: Foldable<G>): FoldableComposition<F, G>

Added in v2.0.0

toArray

Use toReadonlyArray instead

Signature

export declare const toArray: typeof toReadonlyArray

Added in v2.8.0