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fp-ts

ReaderTask overview

Added in v2.3.0

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: {
  <R1, A, R2, _>(self: ReaderTask<R1, A>, f: (a: A) => ReaderTask<R2, _>): ReaderTask<R1 & R2, A>
  <A, R2, _>(f: (a: A) => ReaderTask<R2, _>): <R1>(self: ReaderTask<R1, A>) => ReaderTask<R2 & R1, A>
}

Added in v2.15.0

tapIO

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 tapIO: {
  <A, _>(f: (a: A) => IO<_>): <R>(self: ReaderTask<R, A>) => ReaderTask<R, A>
  <R, A, _>(self: ReaderTask<R, A>, f: (a: A) => IO<_>): ReaderTask<R, A>
}

Example

import { pipe } from 'fp-ts/function'
import * as RT from 'fp-ts/ReaderTask'
import * as Console from 'fp-ts/Console'

// Will produce `Hello, fp-ts` to the stdout
const effect = pipe(
  RT.ask<string>(),
  RT.tapIO((value) => Console.log(`Hello, ${value}`))
)

async function test() {
  assert.deepStrictEqual(await effect('fp-ts')(), 'fp-ts')
}

test()

Added in v2.16.0

tapReader

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 tapReader: {
  <R2, A, _>(f: (a: A) => R.Reader<R2, _>): <R1>(self: ReaderTask<R1, A>) => ReaderTask<R1 & R2, A>
  <R1, R2, A, _>(self: ReaderTask<R1, A>, f: (a: A) => R.Reader<R2, _>): ReaderTask<R1 & R2, A>
}

Added in v2.16.0

tapReaderIO

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 tapReaderIO: {
  <R2, A, _>(f: (a: A) => RIO.ReaderIO<R2, _>): <R1>(self: ReaderTask<R1, A>) => ReaderTask<R1 & R2, A>
  <R1, R2, A, _>(self: ReaderTask<R1, A>, f: (a: A) => RIO.ReaderIO<R2, _>): ReaderTask<R1 & R2, A>
}

Added in v2.16.0

tapTask

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 tapTask: {
  <A, _>(f: (a: A) => T.Task<_>): <R>(self: ReaderTask<R, A>) => ReaderTask<R, A>
  <R, A, _>(self: ReaderTask<R, A>, f: (a: A) => T.Task<_>): ReaderTask<R, A>
}

Example

import { pipe } from 'fp-ts/function'
import * as RT from 'fp-ts/ReaderTask'
import * as T from 'fp-ts/Task'

const effect = pipe(
  RT.ask<number>(),
  RT.tapTask((value) => T.of(value + 1))
)

async function test() {
  assert.deepStrictEqual(await effect(1)(), 1)
}

test()

Added in v2.16.0

constructors

ask

Reads the current context.

Signature

export declare const ask: <R>() => ReaderTask<R, R>

Added in v2.3.0

asks

Projects a value from the global context in a ReaderTask.

Signature

export declare const asks: <R, A>(f: (r: R) => A) => ReaderTask<R, A>

Added in v2.3.0

asksReaderTask

Effectfully accesses the environment.

Signature

export declare const asksReaderTask: <R, A>(f: (r: R) => ReaderTask<R, A>) => ReaderTask<R, A>

Added in v2.11.0

asksReaderTaskW

Less strict version of asksReaderTask.

The W suffix (short for Widening) means that the environment types will be merged.

Signature

export declare const asksReaderTaskW: <R1, R2, A>(f: (r1: R1) => ReaderTask<R2, A>) => ReaderTask<R1 & R2, A>

Added in v2.11.0

of

Signature

export declare const of: <R = unknown, A = never>(a: A) => ReaderTask<R, A>

Added in v2.3.0

conversions

fromIO

Signature

export declare const fromIO: <A, R = unknown>(fa: IO<A>) => ReaderTask<R, A>

Added in v2.3.0

fromReader

Signature

export declare const fromReader: <R, A>(fa: R.Reader<R, A>) => ReaderTask<R, A>

Added in v2.3.0

fromReaderIO

Signature

export declare const fromReaderIO: <R, A>(fa: RIO.ReaderIO<R, A>) => ReaderTask<R, A>

Added in v2.13.0

fromTask

Signature

export declare const fromTask: <A, R = unknown>(fa: T.Task<A>) => ReaderTask<R, A>

Added in v2.3.0

do notation

Do

Signature

export declare const Do: ReaderTask<unknown, {}>

Added in v2.9.0

apS

Signature

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

Added in v2.8.0

apSW

Less strict version of apS.

The W suffix (short for Widening) means that the environment types will be merged.

Signature

export declare const apSW: <A, N extends string, R2, B>(
  name: Exclude<N, keyof A>,
  fb: ReaderTask<R2, B>
) => <R1>(fa: ReaderTask<R1, A>) => ReaderTask<R1 & R2, { 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) => ReaderTask<E, B>
) => (ma: ReaderTask<E, A>) => ReaderTask<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: ReaderTask<E, A>) => ReaderTask<E, { readonly [K in N]: A }>

Added in v2.8.0

bindW

The W suffix (short for Widening) means that the environment types will be merged.

Signature

export declare const bindW: <N extends string, A, R2, B>(
  name: Exclude<N, keyof A>,
  f: (a: A) => ReaderTask<R2, B>
) => <R1>(fa: ReaderTask<R1, A>) => ReaderTask<R1 & R2, { readonly [K in N | keyof A]: K extends keyof A ? A[K] : B }>

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: ReaderTask<E, A>) => ReaderTask<E, { readonly [K in N | keyof A]: K extends keyof A ? A[K] : B }>

Added in v2.13.0

instances

ApplicativePar

Runs computations in parallel.

Signature

export declare const ApplicativePar: Applicative2<'ReaderTask'>

Added in v2.7.0

ApplicativeSeq

Runs computations sequentially.

Signature

export declare const ApplicativeSeq: Applicative2<'ReaderTask'>

Added in v2.7.0

ApplyPar

Runs computations in parallel.

Signature

export declare const ApplyPar: Apply2<'ReaderTask'>

Added in v2.10.0

ApplySeq

Runs computations sequentially.

Signature

export declare const ApplySeq: Apply2<'ReaderTask'>

Added in v2.10.0

Chain

Signature

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

Added in v2.10.0

FromIO

Signature

export declare const FromIO: FromIO2<'ReaderTask'>

Added in v2.10.0

FromReader

Signature

export declare const FromReader: FromReader2<'ReaderTask'>

Added in v2.11.0

FromTask

Signature

export declare const FromTask: FromTask2<'ReaderTask'>

Added in v2.10.0

Functor

Signature

export declare const Functor: Functor2<'ReaderTask'>

Added in v2.7.0

Monad

Signature

export declare const Monad: Monad2<'ReaderTask'>

Added in v2.10.0

MonadIO

Signature

export declare const MonadIO: MonadIO2<'ReaderTask'>

Added in v2.10.0

MonadTask

Signature

export declare const MonadTask: MonadTask2<'ReaderTask'>

Added in v2.10.0

Pointed

Signature

export declare const Pointed: Pointed2<'ReaderTask'>

Added in v2.10.0

legacy

chain

Alias of flatMap.

Signature

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

Added in v2.3.0

chainFirst

Alias of tap.

Signature

export declare const chainFirst: <A, R, B>(
  f: (a: A) => ReaderTask<R, B>
) => (first: ReaderTask<R, A>) => ReaderTask<R, A>

Added in v2.3.0

chainFirstIOK

Alias of tapIO.

Signature

export declare const chainFirstIOK: <A, B>(f: (a: A) => IO<B>) => <R>(first: ReaderTask<R, A>) => ReaderTask<R, A>

Added in v2.10.0

chainFirstReaderIOK

Alias of tapReaderIO.

Signature

export declare const chainFirstReaderIOK: <A, R, B>(
  f: (a: A) => RIO.ReaderIO<R, B>
) => (ma: ReaderTask<R, A>) => ReaderTask<R, A>

Added in v2.13.0

chainFirstReaderIOKW

Alias of tapReaderIO.

Less strict version of chainFirstReaderIOK.

Signature

export declare const chainFirstReaderIOKW: <A, R2, B>(
  f: (a: A) => RIO.ReaderIO<R2, B>
) => <R1>(ma: ReaderTask<R1, A>) => ReaderTask<R1 & R2, A>

Added in v2.13.0

chainFirstReaderK

Alias of tapReader.

Signature

export declare const chainFirstReaderK: <A, R, B>(
  f: (a: A) => R.Reader<R, B>
) => (ma: ReaderTask<R, A>) => ReaderTask<R, A>

Added in v2.11.0

chainFirstReaderKW

Alias of tapReader.

Less strict version of chainFirstReaderK.

The W suffix (short for Widening) means that the environment types will be merged.

Signature

export declare const chainFirstReaderKW: <A, R1, B>(
  f: (a: A) => R.Reader<R1, B>
) => <R2>(ma: ReaderTask<R2, A>) => ReaderTask<R1 & R2, A>

Added in v2.11.0

chainFirstTaskK

Alias of tapTask.

Signature

export declare const chainFirstTaskK: <A, B>(f: (a: A) => T.Task<B>) => <R>(first: ReaderTask<R, A>) => ReaderTask<R, A>

Added in v2.10.0

chainFirstW

Alias of tap.

Signature

export declare const chainFirstW: <R2, A, B>(
  f: (a: A) => ReaderTask<R2, B>
) => <R1>(ma: ReaderTask<R1, A>) => ReaderTask<R1 & R2, A>

Added in v2.11.0

chainIOK

Alias of flatMapIO.

Signature

export declare const chainIOK: <A, B>(f: (a: A) => IO<B>) => <R>(first: ReaderTask<R, A>) => ReaderTask<R, B>

Added in v2.4.0

chainReaderIOK

Alias of flatMapReaderIO.

Signature

export declare const chainReaderIOK: <A, R, B>(
  f: (a: A) => RIO.ReaderIO<R, B>
) => (ma: ReaderTask<R, A>) => ReaderTask<R, B>

Added in v2.13.0

chainReaderIOKW

Alias of flatMapReaderIO.

Less strict version of chainReaderIOK.

Signature

export declare const chainReaderIOKW: <A, R2, B>(
  f: (a: A) => RIO.ReaderIO<R2, B>
) => <R1>(ma: ReaderTask<R1, A>) => ReaderTask<R1 & R2, B>

Added in v2.13.0

chainReaderK

Alias of flatMapReader.

Signature

export declare const chainReaderK: <A, R, B>(f: (a: A) => R.Reader<R, B>) => (ma: ReaderTask<R, A>) => ReaderTask<R, B>

Added in v2.11.0

chainReaderKW

Alias of flatMapReader.

Less strict version of chainReaderK.

The W suffix (short for Widening) means that the environment types will be merged.

Signature

export declare const chainReaderKW: <A, R1, B>(
  f: (a: A) => R.Reader<R1, B>
) => <R2>(ma: ReaderTask<R2, A>) => ReaderTask<R1 & R2, B>

Added in v2.11.0

chainTaskK

Alias of flatMapTask.

Signature

export declare const chainTaskK: <A, B>(f: (a: A) => T.Task<B>) => <R>(first: ReaderTask<R, A>) => ReaderTask<R, B>

Added in v2.4.0

chainW

Alias of flatMap.

Signature

export declare const chainW: <R2, A, B>(
  f: (a: A) => ReaderTask<R2, B>
) => <R1>(ma: ReaderTask<R1, A>) => ReaderTask<R1 & R2, B>

Added in v2.6.7

lifting

fromIOK

Signature

export declare const fromIOK: <A extends readonly unknown[], B>(
  f: (...a: A) => IO<B>
) => <R = unknown>(...a: A) => ReaderTask<R, B>

Added in v2.4.0

fromReaderIOK

Signature

export declare const fromReaderIOK: <A extends readonly unknown[], R, B>(
  f: (...a: A) => RIO.ReaderIO<R, B>
) => (...a: A) => ReaderTask<R, B>

Added in v2.13.0

fromReaderK

Signature

export declare const fromReaderK: <A extends readonly unknown[], R, B>(
  f: (...a: A) => R.Reader<R, B>
) => (...a: A) => ReaderTask<R, B>

Added in v2.11.0

fromTaskK

Signature

export declare const fromTaskK: <A extends readonly unknown[], B>(
  f: (...a: A) => T.Task<B>
) => <R = unknown>(...a: A) => ReaderTask<R, B>

Added in v2.4.0

mapping

as

Maps the value to the specified constant value.

Signature

export declare const as: {
  <A>(a: A): <R, _>(self: ReaderTask<R, _>) => ReaderTask<R, A>
  <R, _, A>(self: ReaderTask<R, _>, a: A): ReaderTask<R, A>
}

Added in v2.16.0

asUnit

Maps the value to the void constant value.

Signature

export declare const asUnit: <R, _>(self: ReaderTask<R, _>) => ReaderTask<R, void>

Added in v2.16.0

flap

Signature

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

Added in v2.3.0

model

ReaderTask (interface)

Signature

export interface ReaderTask<R, A> {
  (r: R): Task<A>
}

Added in v2.3.0

sequencing

flatMap

Signature

export declare const flatMap: {
  <A, R2, B>(f: (a: A) => ReaderTask<R2, B>): <R1>(ma: ReaderTask<R1, A>) => ReaderTask<R1 & R2, B>
  <R1, A, R2, B>(ma: ReaderTask<R1, A>, f: (a: A) => ReaderTask<R2, B>): ReaderTask<R1 & R2, B>
}

Added in v2.14.0

flatMapIO

Signature

export declare const flatMapIO: {
  <A, B>(f: (a: A) => IO<B>): <R>(self: ReaderTask<R, A>) => ReaderTask<R, B>
  <R, A, B>(self: ReaderTask<R, A>, f: (a: A) => IO<B>): ReaderTask<R, B>
}

Added in v2.16.0

flatMapReader

Signature

export declare const flatMapReader: {
  <A, R2, B>(f: (a: A) => R.Reader<R2, B>): <R1>(self: ReaderTask<R1, A>) => ReaderTask<R1 & R2, B>
  <R1, A, R2, B>(self: ReaderTask<R1, A>, f: (a: A) => R.Reader<R2, B>): ReaderTask<R1 & R2, B>
}

Added in v2.16.0

flatMapReaderIO

Signature

export declare const flatMapReaderIO: {
  <A, R2, B>(f: (a: A) => RIO.ReaderIO<R2, B>): <R1>(self: ReaderTask<R1, A>) => ReaderTask<R1 & R2, B>
  <R1, A, R2, B>(self: ReaderTask<R1, A>, f: (a: A) => RIO.ReaderIO<R2, B>): ReaderTask<R1 & R2, B>
}

Added in v2.16.0

flatMapTask

Signature

export declare const flatMapTask: {
  <A, B>(f: (a: A) => T.Task<B>): <R>(self: ReaderTask<R, A>) => ReaderTask<R, B>
  <R, A, B>(self: ReaderTask<R, A>, f: (a: A) => T.Task<B>): ReaderTask<R, B>
}

Added in v2.16.0

flatten

Signature

export declare const flatten: <R, A>(mma: ReaderTask<R, ReaderTask<R, A>>) => ReaderTask<R, A>

Added in v2.3.0

flattenW

Less strict version of flatten.

The W suffix (short for Widening) means that the environment types will be merged.

Signature

export declare const flattenW: <R1, R2, A>(mma: ReaderTask<R1, ReaderTask<R2, A>>) => ReaderTask<R1 & R2, A>

Added in v2.11.0

traversing

sequenceArray

Equivalent to ReadonlyArray#sequence(Applicative).

Signature

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

Added in v2.9.0

traverseArray

Equivalent to ReadonlyArray#traverseWithIndex(Applicative).

Signature

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

Added in v2.9.0

traverseArrayWithIndex

Equivalent to ReadonlyArray#traverseWithIndex(Applicative).

Signature

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

Added in v2.9.0

traverseReadonlyArrayWithIndex

Equivalent to ReadonlyArray#traverseWithIndex(Applicative).

Signature

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

Added in v2.11.0

traverseReadonlyArrayWithIndexSeq

Equivalent to ReadonlyArray#traverseWithIndex(ApplicativeSeq).

Signature

export declare const traverseReadonlyArrayWithIndexSeq: <R, A, B>(
  f: (index: number, a: A) => ReaderTask<R, B>
) => (as: readonly A[]) => ReaderTask<R, readonly B[]>

Added in v2.11.0

traverseReadonlyNonEmptyArrayWithIndex

Equivalent to ReadonlyNonEmptyArray#traverseWithIndex(Applicative).

Signature

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

Added in v2.11.0

traverseReadonlyNonEmptyArrayWithIndexSeq

Equivalent to ReadonlyNonEmptyArray#traverseWithIndex(ApplicativeSeq).

Signature

export declare const traverseReadonlyNonEmptyArrayWithIndexSeq: <R, A, B>(
  f: (index: number, a: A) => ReaderTask<R, B>
) => (as: ReadonlyNonEmptyArray<A>) => ReaderTask<R, ReadonlyNonEmptyArray<B>>

Added in v2.11.0

traverseSeqArray

Equivalent to ReadonlyArray#traverse(ApplicativeSeq).

Signature

export declare const traverseSeqArray: <R, A, B>(
  f: (a: A) => ReaderTask<R, B>
) => (as: readonly A[]) => ReaderTask<R, readonly B[]>

Added in v2.10.0

traverseSeqArrayWithIndex

Equivalent to ReadonlyArray#traverseWithIndex(ApplicativeSeq).

Signature

export declare const traverseSeqArrayWithIndex: <R, A, B>(
  f: (index: number, a: A) => ReaderTask<R, B>
) => (as: readonly A[]) => ReaderTask<R, readonly B[]>

Added in v2.10.0

type lambdas

URI

Signature

export declare const URI: 'ReaderTask'

Added in v2.3.0

URI (type alias)

Signature

export type URI = typeof URI

Added in v2.3.0

utils

ApT

Signature

export declare const ApT: ReaderTask<unknown, readonly []>

Added in v2.11.0

ap

Signature

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

Added in v2.3.0

apFirst

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

Signature

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

Added in v2.3.0

apSecond

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

Signature

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

Added in v2.3.0

apW

Less strict version of ap.

The W suffix (short for Widening) means that the environment types will be merged.

Signature

export declare const apW: <R2, A>(
  fa: ReaderTask<R2, A>
) => <R1, B>(fab: ReaderTask<R1, (a: A) => B>) => ReaderTask<R1 & R2, B>

Added in v2.8.0

local

Changes the value of the local context during the execution of the action ma (similar to Contravariant’s contramap).

Signature

export declare const local: <R2, R1>(f: (r2: R2) => R1) => <A>(ma: ReaderTask<R1, A>) => ReaderTask<R2, A>

Added in v2.3.0

zone of death

getMonoid

Use getApplicativeMonoid instead.

Signature

export declare const getMonoid: <R, A>(M: Monoid<A>) => Monoid<ReaderTask<R, A>>

Added in v2.3.0

getSemigroup

Use getApplySemigroup instead.

Signature

export declare const getSemigroup: <R, A>(S: Semigroup<A>) => Semigroup<ReaderTask<R, A>>

Added in v2.3.0

readerTaskSeq

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

Signature

export declare const readerTaskSeq: MonadTask2<'ReaderTask'>

Added in v2.3.0

readerTask

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

Signature

export declare const readerTask: MonadTask2<'ReaderTask'>

Added in v2.3.0

run

Signature

export declare function run<R, A>(ma: ReaderTask<R, A>, r: R): Promise<A>

Added in v2.4.0

sequenceSeqArray

Use traverseReadonlyArrayWithIndexSeq instead.

Signature

export declare const sequenceSeqArray: <R, A>(arr: readonly ReaderTask<R, A>[]) => ReaderTask<R, readonly A[]>

Added in v2.10.0