State.ts.md

title	nav_order	parent
State.ts	97	Modules

State overview

Added in v2.0.0

---

Table of contents

• Apply
  • ap
• Functor
  • map
• Monad
  • chain
• Pointed
  • of
• combinators
  • apFirst
  • apSecond
  • chainFirst
  • flap
  • flatten
• constructors
  • get
  • gets
  • modify
  • put
• instances
  • Applicative
  • Apply
  • Chain
  • FromState
  • Functor
  • Monad
  • Pointed
  • URI
  • URI (type alias)
  • state
• model
  • State (interface)
• utils
  • apS
  • bind
  • bindTo
  • evaluate
  • execute
  • sequenceArray
  • sequenceNonEmptyArray
  • traverseArray
  • traverseArrayWithIndex
  • traverseReadonlyArrayWithIndex
  • traverseReadonlyNonEmptyArrayWithIndex
  • evalState
  • execState

---

Apply

ap

Apply a function to an argument under a type constructor.

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

Functor

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

Monad

chain

Composes computations in sequence, using the return value of one computation to determine the next computation.

Signature

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

Added in v2.0.0

Pointed

of

Signature

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

Added in v2.0.0

combinators

apFirst

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

Derivable from Apply.

Signature

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

Added in v2.0.0

apSecond

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

Derivable from Apply.

Signature

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

Added in v2.0.0

chainFirst

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

Derivable from Chain.

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

flap

Derivable from Functor.

Signature

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

Added in v2.10.0

flatten

Derivable from Chain.

Signature

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

Added in v2.0.0

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

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: 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

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

state

Use small, specific instances instead.

Signature

export declare const state: Monad2<'State'>

Added in v2.0.0

model

State (interface)

Signature

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

Added in v2.0.0

utils

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

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

sequenceArray

Signature

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

Added in v2.9.0

sequenceNonEmptyArray

Signature

export declare const sequenceNonEmptyArray: <S, A>(
  arr: ReadonlyNonEmptyArray<State<S, A>>
) => State<S, ReadonlyNonEmptyArray<A>>

Added in v2.12.0

traverseArray

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

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

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