Skip to main content

Reader

Instances​

Combinators​

Constructors​

Do notation​

Instance methods​

Legacy​

Mapping​

Model​

Sequencing​

Traversing​

Type lambdas​

Utilities​

Instances​

Applicative​

Signature​

export declare const Applicative: Applicative2<URI>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

Apply​

Signature​

export declare const Apply: Apply2<URI>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

Category​

Signature​

export declare const Category: Category2<URI>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

Chain​

Signature​

export declare const Chain: chainable.Chain2<URI>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

ChainRec​

ChainRec for Reader

Signature​

export declare const ChainRec: ChainRec2<URI>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2022-present Jacob Alford

Choice​

Signature​

export declare const Choice: Choice2<URI>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

Functor​

Signature​

export declare const Functor: Functor2<URI>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

Monad​

Signature​

export declare const Monad: Monad2<URI>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

Pointed​

Signature​

export declare const Pointed: Pointed2<URI>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

Profunctor​

Signature​

export declare const Profunctor: Profunctor2<URI>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

Strong​

Signature​

export declare const Strong: Strong2<URI>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

Constructors​

ask​

Reads the current context

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

asks​

Projects a value from the global context in a Reader

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

asksReader​

Effectfully accesses the environment.

Signature​

export declare const asksReader: <R, A>(f: (r: R) => Reader<R, A>) => Reader<R, A>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

asksReaderW​

Less strict version of asksReader.

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

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

id​

Signature​

export declare const id: Category2<URI>['id']

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

of​

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

Do notation​

Do​

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

apS​

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

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: Reader<R2, B>,
) => <R1>(fa: Reader<R1, A>) => Reader<
  R1 & R2,
  {
    readonly [K in keyof A | N]: K extends keyof A ? A[K] : B
  }
>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

bind​

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

bindTo​

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

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) => Reader<R2, B>,
) => <R1>(fa: Reader<R1, A>) => Reader<
  R1 & R2,
  {
    readonly [K in keyof A | N]: K extends keyof A ? A[K] : B
  }
>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

Instance methods​

chainRec​

Signature​

export declare const chainRec: ChainRec2<URI>['chainRec']

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2022-present Jacob Alford

Legacy​

chain​

Alias of flatMap.

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

chainFirst​

Alias of tap.

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

chainFirstW​

Alias of tap.

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

chainW​

Alias of flatMap.

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

Mapping​

flap​

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

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: Reader<R, A>) => Reader<R, B>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

Model​

Reader​

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

Sequencing​

flatMap​

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

flatten​

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

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: Reader<R1, Reader<R2, A>>) => Reader<R1 & R2, A>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

Traversing​

sequenceArray​

Equivalent to ReadonlyArray#sequence(Applicative).

Signature​

export declare const sequenceArray: <R, A>(arr: ReadonlyArray<Reader<R, A>>) => Reader<R, ReadonlyArray<A>>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

traverseArray​

Equivalent to ReadonlyArray#traverse(Applicative).

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

traverseArrayWithIndex​

Equivalent to ReadonlyArray#traverseWithIndex(Applicative).

Signature​

export declare const traverseArrayWithIndex: <R, A, B>(
  f: (index: number, a: A) => Reader<R, B>,
) => (as: ReadonlyArray<A>) => Reader<R, ReadonlyArray<B>>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

traverseReadonlyArrayWithIndex​

Equivalent to ReadonlyArray#traverseWithIndex(Applicative).

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

traverseReadonlyNonEmptyArrayWithIndex​

Equivalent to ReadonlyNonEmptyArray#traverseWithIndex(Applicative).

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

Type lambdas​

URI​

Signature​

export type URI = typeof URI

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

URI​

Signature​

export declare const URI = 'Reader'

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

Utilities​

ApT​

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

ap​

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

apFirst​

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

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

apFirstW​

Less strict version of apFirst.

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

Signature​

export declare const apFirstW: <R2, B>(second: Reader<R2, B>) => <R1, A>(first: Reader<R1, A>) => Reader<R1 & R2, A>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

apSecond​

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

Signature​

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

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

apSecondW​

Less strict version of apSecond.

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

Signature​

export declare const apSecondW: <R2, B>(second: Reader<R2, B>) => <R1, A>(first: Reader<R1, A>) => Reader<R1 & R2, B>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

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: Reader<R2, A>) => <R1, B>(fab: Reader<R1, (a: A) => B>) => Reader<R1 & R2, B>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

compose​

Signature​

export declare const compose: <A, B>(ab: Reader<A, B>) => <C>(bc: Reader<B, C>) => Reader<A, C>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

do​

Signature​

export declare const do_: <MA extends ReaderIterable<any, any>, A>(
  yieldFunction: (unwrap: <R, A>(ma: Reader<R, A>) => ReaderIterable<R, A>) => Generator<MA, A>,
) => Reader<_.UnionToIntersection<MA extends ReaderIterable<infer R, any> ? R : never>, A>

first​

Signature​

export declare const first: Strong2<URI>['first']

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

getMonoid​

Use getApplicativeMonoid instead.

Signature​

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

Details​

  • Added in 0.1.0
  • Deprecated

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

getSemigroup​

Use getApplySemigroup instead.

Signature​

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

Details​

  • Added in 0.1.0
  • Deprecated

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

left​

Signature​

export declare const left: Choice2<URI>['left']

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

let​

Signature​

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

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: Reader<R1, A>) => Reader<R2, A>

Details​

  • Added in 0.1.0

Example​

import { pipe } from '@fp-tx/core/function'
import * as R from '@fp-tx/core/Reader'
import * as string from '@fp-tx/core/string'

const calculateContentLen: R.Reader<string, number> = pipe(
  R.Do,
  R.bind('content', () => R.ask<string>()),
  R.map(({ content }) => string.size(content)),
)

// Calls calculateContentLen after adding a prefix to the Reader content.
const calculateModifiedContentLen: R.Reader<string, number> = pipe(
  calculateContentLen,
  R.local(s => 'Prefix ' + s),
)

const s = '12345'

assert.deepStrictEqual(
  "Modified 's' length: " +
    calculateModifiedContentLen(s) +
    '\n' +
    "Original 's' length: " +
    calculateContentLen(s),
  "Modified 's' length: 12\nOriginal 's' length: 5",
)

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

promap​

Signature​

export declare const promap: <E, A, D, B>(f: (d: D) => E, g: (a: A) => B) => (fea: Reader<E, A>) => Reader<D, B>

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

reader​

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

Signature​

export declare const reader: Monad2<URI> & Profunctor2<URI> & Category2<URI> & Strong2<URI> & Choice2<URI>

Details​

  • Added in 0.1.0
  • Deprecated

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

Signature​

export declare const right: Choice2<URI>['right']

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti

second​

Signature​

export declare const second: Strong2<URI>['second']

Details​

  • Added in 0.1.0

License​

  • MIT – Copyright (c) 2017-present Giulio Canti