State overview

Added in v2.0.0

Table of contents

combinators

tap

Composes computations in sequence, using the return value of one computation to determine the next computation and keeping only the result of the first.

Signature

export declare const tap: {
  <S, A, _>(self: State<S, A>, f: (a: A) => State<S, _>): State<S, A>
  <A, S, _>(f: (a: A) => State<S, _>): (self: State<S, A>) => State<S, A>
}

Added in v2.15.0

constructors

get

Get the current state

Signature

export declare const get: <S>() => State<S, S>

Added in v2.0.0

gets

Get a value which depends on the current state

Signature

export declare const gets: <S, A>(f: (s: S) => A) => State<S, A>

Added in v2.0.0

modify

Modify the state by applying a function to the current state

Signature

export declare const modify: <S>(f: (s: S) => S) => State<S, void>

Added in v2.0.0

of

Signature

export declare const of: <S, A>(a: A) => State<S, A>

Added in v2.0.0

put

Set the state

Signature

export declare const put: <S>(s: S) => State<S, void>

Added in v2.0.0

instances

Applicative

Signature

export declare const Applicative: Applicative2<'State'>

Added in v2.7.0

Apply

Signature

export declare const Apply: Apply2<'State'>

Added in v2.10.0

Chain

Signature

export declare const Chain: chainable.Chain2<'State'>

Added in v2.10.0

FromState

Signature

export declare const FromState: FromState2<'State'>

Added in v2.11.0

Functor

Signature

export declare const Functor: Functor2<'State'>

Added in v2.7.0

Monad

Signature

export declare const Monad: Monad2<'State'>

Added in v2.7.0

Pointed

Signature

export declare const Pointed: Pointed2<'State'>

Added in v2.10.0

legacy

chain

Alias of flatMap.

Signature

export declare const chain: <S, A, B>(f: (a: A) => State<S, B>) => (ma: State<S, A>) => State<S, B>

Added in v2.0.0

chainFirst

Alias of tap.

Signature

export declare const chainFirst: <S, A, B>(f: (a: A) => State<S, B>) => (ma: State<S, A>) => State<S, A>

Added in v2.0.0

mapping

flap

Signature

export declare const flap: <A>(a: A) => <E, B>(fab: State<E, (a: A) => B>) => State<E, B>

Added in v2.10.0

map

map can be used to turn functions (a: A) => B into functions (fa: F<A>) => F<B> whose argument and return types use the type constructor F to represent some computational context.

Signature

export declare const map: <A, B>(f: (a: A) => B) => <E>(fa: State<E, A>) => State<E, B>

Added in v2.0.0

model

State (interface)

Signature

export interface State<S, A> {
  (s: S): [A, S]
}

Added in v2.0.0

sequencing

flatMap

Signature

export declare const flatMap: {
  <A, S, B>(f: (a: A) => State<S, B>): (ma: State<S, A>) => State<S, B>
  <S, A, B>(ma: State<S, A>, f: (a: A) => State<S, B>): State<S, B>
}

Added in v2.14.0

flatten

Signature

export declare const flatten: <E, A>(mma: State<E, State<E, A>>) => State<E, A>

Added in v2.0.0

traversing

sequenceArray

Equivalent to ReadonlyArray#sequence(Applicative).

Signature

export declare const sequenceArray: <S, A>(arr: readonly State<S, A>[]) => State<S, readonly A[]>

Added in v2.9.0

traverseArray

Equivalent to ReadonlyArray#traverse(Applicative).

Signature

export declare const traverseArray: <A, S, B>(f: (a: A) => State<S, B>) => (as: readonly A[]) => State<S, readonly B[]>

Added in v2.9.0

traverseArrayWithIndex

Equivalent to ReadonlyArray#traverseWithIndex(Applicative).

Signature

export declare const traverseArrayWithIndex: <A, S, B>(
  f: (index: number, a: A) => State<S, B>
) => (as: readonly A[]) => State<S, readonly B[]>

Added in v2.9.0

traverseReadonlyArrayWithIndex

Equivalent to ReadonlyArray#traverseWithIndex(Applicative).

Signature

export declare const traverseReadonlyArrayWithIndex: <A, S, B>(
  f: (index: number, a: A) => State<S, B>
) => (as: readonly A[]) => State<S, readonly B[]>

Added in v2.11.0

traverseReadonlyNonEmptyArrayWithIndex

Equivalent to ReadonlyNonEmptyArray#traverseWithIndex(Applicative).

Signature

export declare const traverseReadonlyNonEmptyArrayWithIndex: <A, S, B>(
  f: (index: number, a: A) => State<S, B>
) => (as: ReadonlyNonEmptyArray<A>) => State<S, ReadonlyNonEmptyArray<B>>

Added in v2.11.0

type lambdas

URI

Signature

export declare const URI: 'State'

Added in v2.0.0

URI (type alias)

Signature

export type URI = typeof URI

Added in v2.0.0

utils

ap

Signature

export declare const ap: <E, A>(fa: State<E, A>) => <B>(fab: State<E, (a: A) => B>) => State<E, B>

Added in v2.0.0

apFirst

Combine two effectful actions, keeping only the result of the first.

Signature

export declare const apFirst: <E, B>(second: State<E, B>) => <A>(first: State<E, A>) => State<E, A>

Added in v2.0.0

apS

Signature

export declare const apS: <N, A, E, B>(
  name: Exclude<N, keyof A>,
  fb: State<E, B>
) => (fa: State<E, A>) => State<E, { readonly [K in N | keyof A]: K extends keyof A ? A[K] : B }>

Added in v2.8.0

apSecond

Combine two effectful actions, keeping only the result of the second.

Signature

export declare const apSecond: <E, B>(second: State<E, B>) => <A>(first: State<E, A>) => State<E, B>

Added in v2.0.0

bind

Signature

export declare const bind: <N, A, E, B>(
  name: Exclude<N, keyof A>,
  f: (a: A) => State<E, B>
) => (ma: State<E, A>) => State<E, { readonly [K in N | keyof A]: K extends keyof A ? A[K] : B }>

Added in v2.8.0

bindTo

Signature

export declare const bindTo: <N>(name: N) => <E, A>(fa: State<E, A>) => State<E, { readonly [K in N]: A }>

Added in v2.8.0

evaluate

Run a computation in the State monad, discarding the final state

Signature

export declare const evaluate: <S>(s: S) => <A>(ma: State<S, A>) => A

Added in v2.8.0

execute

Run a computation in the State monad discarding the result

Signature

export declare const execute: <S>(s: S) => <A>(ma: State<S, A>) => S

Added in v2.8.0

let

Signature

export declare const let: <N, A, B>(
  name: Exclude<N, keyof A>,
  f: (a: A) => B
) => <E>(fa: State<E, A>) => State<E, { readonly [K in N | keyof A]: K extends keyof A ? A[K] : B }>

Added in v2.13.0

zone of death

evalState

Use evaluate instead

Signature

export declare const evalState: <S, A>(ma: State<S, A>, s: S) => A

Added in v2.0.0

execState

Use execute instead

Signature

export declare const execState: <S, A>(ma: State<S, A>, s: S) => S

Added in v2.0.0

state

This instance is deprecated, use small, specific instances instead. For example if a function needs a Functor instance, pass S.Functor instead of S.state (where S is from import S from 'fp-ts/State')

Signature

export declare const state: Monad2<'State'>

Added in v2.0.0