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fp-ts

ReaderEither 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: {
  <R1, E1, A, R2, E2, _>(self: ReaderEither<R1, E1, A>, f: (a: A) => ReaderEither<R2, E2, _>): ReaderEither<
    R1 & R2,
    E1 | E2,
    A
  >
  <A, R2, E2, _>(f: (a: A) => ReaderEither<R2, E2, _>): <R1, E1>(
    self: ReaderEither<R1, E1, A>
  ) => ReaderEither<R1 & R2, E2 | E1, A>
}

Added in v2.15.0

tapEither

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 tapEither: {
  <A, E2, _>(f: (a: A) => E.Either<E2, _>): <R1, E1>(self: ReaderEither<R1, E1, A>) => ReaderEither<R1, E2 | E1, A>
  <R1, E1, A, E2, _>(self: ReaderEither<R1, E1, A>, f: (a: A) => E.Either<E2, _>): ReaderEither<R1, E1 | E2, A>
}

Example

import * as E from 'fp-ts/Either'
import { pipe } from 'fp-ts/function'
import * as RE from 'fp-ts/ReaderEither'

const checkString = (value: string) =>
  pipe(
    RE.ask<number>(),
    RE.tapEither((minLength) => (value.length > minLength ? E.right('ok') : E.left('error')))
  )

assert.deepStrictEqual(checkString('')(1), E.left('error'))
assert.deepStrictEqual(checkString('fp-ts')(2), E.right(2))

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

Added in v2.16.0

constructors

ask

Reads the current context.

Signature

export declare const ask: <R, E = never>() => ReaderEither<R, E, R>

Added in v2.0.0

asks

Projects a value from the global context in a ReaderEither.

Signature

export declare const asks: <R, A, E = never>(f: (r: R) => A) => ReaderEither<R, E, A>

Added in v2.0.0

asksReaderEither

Effectfully accesses the environment.

Signature

export declare const asksReaderEither: <R, E, A>(f: (r: R) => ReaderEither<R, E, A>) => ReaderEither<R, E, A>

Added in v2.11.0

asksReaderEitherW

Less strict version of asksReaderEither.

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

Signature

export declare const asksReaderEitherW: <R1, R2, E, A>(
  f: (r1: R1) => ReaderEither<R2, E, A>
) => ReaderEither<R1 & R2, E, A>

Added in v2.11.0

left

Signature

export declare const left: <R, E = never, A = never>(e: E) => ReaderEither<R, E, A>

Added in v2.0.0

leftReader

Signature

export declare const leftReader: <R, E = never, A = never>(me: R.Reader<R, E>) => ReaderEither<R, E, A>

Added in v2.0.0

of

Signature

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

Added in v2.8.5

Signature

export declare const right: <R, E = never, A = never>(a: A) => ReaderEither<R, E, A>

Added in v2.0.0

rightReader

Signature

export declare const rightReader: <R, E = never, A = never>(ma: R.Reader<R, A>) => ReaderEither<R, E, A>

Added in v2.0.0

conversions

fromEither

Signature

export declare const fromEither: <E, A, R = unknown>(fa: E.Either<E, A>) => ReaderEither<R, E, A>

Added in v2.0.0

fromOption

Signature

export declare const fromOption: <E>(onNone: LazyArg<E>) => <A, R = unknown>(fa: Option<A>) => ReaderEither<R, E, A>

Added in v2.0.0

fromReader

Signature

export declare const fromReader: <R, A, E = never>(fa: R.Reader<R, A>) => ReaderEither<R, E, A>

Added in v2.11.0

toUnion

Signature

export declare const toUnion: <R, E, A>(fa: ReaderEither<R, E, A>) => R.Reader<R, E | A>

Added in v2.10.0

do notation

Do

Signature

export declare const Do: ReaderEither<unknown, never, {}>

Added in v2.9.0

apS

Signature

export declare const apS: <N, A, R, E, B>(
  name: Exclude<N, keyof A>,
  fb: ReaderEither<R, E, B>
) => (fa: ReaderEither<R, E, A>) => ReaderEither<R, 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 and the error types will be merged.

Signature

export declare const apSW: <A, N extends string, R2, E2, B>(
  name: Exclude<N, keyof A>,
  fb: ReaderEither<R2, E2, B>
) => <R1, E1>(
  fa: ReaderEither<R1, E1, A>
) => ReaderEither<R1 & R2, E2 | E1, { 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, R, E, B>(
  name: Exclude<N, keyof A>,
  f: (a: A) => ReaderEither<R, E, B>
) => (ma: ReaderEither<R, E, A>) => ReaderEither<R, 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
) => <R, E, A>(fa: ReaderEither<R, E, A>) => ReaderEither<R, E, { readonly [K in N]: A }>

Added in v2.8.0

bindW

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

Signature

export declare const bindW: <N extends string, A, R2, E2, B>(
  name: Exclude<N, keyof A>,
  f: (a: A) => ReaderEither<R2, E2, B>
) => <R1, E1>(
  fa: ReaderEither<R1, E1, A>
) => ReaderEither<R1 & R2, E2 | E1, { 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
) => <R, E>(
  fa: ReaderEither<R, E, A>
) => ReaderEither<R, E, { readonly [K in N | keyof A]: K extends keyof A ? A[K] : B }>

Added in v2.13.0

error handling

alt

Identifies an associative operation on a type constructor. It is similar to Semigroup, except that it applies to types of kind * -> *.

Signature

export declare const alt: <R, E, A>(
  that: () => ReaderEither<R, E, A>
) => (fa: ReaderEither<R, E, A>) => ReaderEither<R, E, A>

Added in v2.0.0

altW

Less strict version of alt.

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

Signature

export declare const altW: <R2, E2, B>(
  that: () => ReaderEither<R2, E2, B>
) => <R1, E1, A>(fa: ReaderEither<R1, E1, A>) => ReaderEither<R1 & R2, E2, B | A>

Added in v2.9.0

getAltReaderValidation

The default Alt instance returns the last error, if you want to get all errors you need to provide a way to concatenate them via a Semigroup.

See getAltValidation.

Signature

export declare function getAltReaderValidation<E>(S: Semigroup<E>): Alt3C<URI, E>

Added in v2.7.0

getApplicativeReaderValidation

The default Applicative instance returns the first error, if you want to get all errors you need to provide a way to concatenate them via a Semigroup.

See getApplicativeValidation.

Signature

export declare function getApplicativeReaderValidation<E>(S: Semigroup<E>): Applicative3C<URI, E>

Added in v2.7.0

getOrElse

Signature

export declare const getOrElse: <E, R, A>(
  onLeft: (e: E) => R.Reader<R, A>
) => (ma: ReaderEither<R, E, A>) => R.Reader<R, A>

Added in v2.0.0

getOrElseW

Less strict version of getOrElse.

The W suffix (short for Widening) means that the handler return type will be merged.

Signature

export declare const getOrElseW: <R2, E, B>(
  onLeft: (e: E) => R.Reader<R2, B>
) => <R1, A>(ma: ReaderEither<R1, E, A>) => R.Reader<R1 & R2, B | A>

Added in v2.6.0

mapBoth

Returns a ReaderEither whose failure and success channels have been mapped by the specified pair of functions, f and g.

Signature

export declare const mapBoth: {
  <E, G, A, B>(f: (e: E) => G, g: (a: A) => B): <R>(self: ReaderEither<R, E, A>) => ReaderEither<R, G, B>
  <R, E, A, G, B>(self: ReaderEither<R, E, A>, f: (e: E) => G, g: (a: A) => B): ReaderEither<R, G, B>
}

Example

import * as ReaderEither from 'fp-ts/ReaderEither'
import * as Either from 'fp-ts/Either'

const f = (s: string) => new Error(s)
const g = (n: number) => n * 2

assert.deepStrictEqual(ReaderEither.mapBoth(ReaderEither.right(1), f, g)({}), Either.right(2))
assert.deepStrictEqual(ReaderEither.mapBoth(ReaderEither.left('err'), f, g)({}), Either.left(new Error('err')))

Added in v2.16.0

mapError

Returns a ReaderEither with its error channel mapped using the specified function.

Signature

export declare const mapError: {
  <R, E, G>(f: (e: E) => G): <A>(self: ReaderEither<R, E, A>) => ReaderEither<R, G, A>
  <R, E, A, G>(self: ReaderEither<R, E, A>, f: (e: E) => G): ReaderEither<R, G, A>
}

Example

import * as ReaderEither from 'fp-ts/ReaderEither'
import * as Either from 'fp-ts/Either'

const f = (s: string) => new Error(s)

assert.deepStrictEqual(ReaderEither.mapError(ReaderEither.right(1), f)({}), Either.right(1))
assert.deepStrictEqual(ReaderEither.mapError(ReaderEither.left('err'), f)({}), Either.left(new Error('err')))

Added in v2.16.0

orElse

Signature

export declare const orElse: <E1, R, E2, A>(
  onLeft: (e: E1) => ReaderEither<R, E2, A>
) => (ma: ReaderEither<R, E1, A>) => ReaderEither<R, E2, A>

Added in v2.0.0

orElseW

Less strict version of orElse.

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

Signature

export declare const orElseW: <E1, R1, E2, B>(
  onLeft: (e: E1) => ReaderEither<R1, E2, B>
) => <R2, A>(ma: ReaderEither<R2, E1, A>) => ReaderEither<R1 & R2, E2, B | A>

Added in v2.10.0

orLeft

Signature

export declare const orLeft: <E1, R, E2>(
  onLeft: (e: E1) => R.Reader<R, E2>
) => <A>(fa: ReaderEither<R, E1, A>) => ReaderEither<R, E2, A>

Added in v2.11.0

tapError

Returns an effect that effectfully “peeks” at the failure of this effect.

Signature

export declare const tapError: {
  <E1, R2, E2, _>(onLeft: (e: E1) => ReaderEither<R2, E2, _>): <R1, A>(
    self: ReaderEither<R1, E1, A>
  ) => ReaderEither<R1 & R2, E1 | E2, A>
  <R1, E1, A, R2, E2, _>(self: ReaderEither<R1, E1, A>, onLeft: (e: E1) => ReaderEither<R2, E2, _>): ReaderEither<
    R1 & R2,
    E1 | E2,
    A
  >
}

Added in v2.15.0

filtering

filterOrElse

Signature

export declare const filterOrElse: {
  <E, A, B extends A>(refinement: Refinement<A, B>, onFalse: (a: A) => E): <R>(
    ma: ReaderEither<R, E, A>
  ) => ReaderEither<R, E, B>
  <E, A>(predicate: Predicate<A>, onFalse: (a: A) => E): <R, B extends A>(
    mb: ReaderEither<R, E, B>
  ) => ReaderEither<R, E, B>
  <E, A>(predicate: Predicate<A>, onFalse: (a: A) => E): <R>(ma: ReaderEither<R, E, A>) => ReaderEither<R, E, A>
}

Added in v2.0.0

filterOrElseW

Less strict version of filterOrElse.

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

Signature

export declare const filterOrElseW: {
  <A, B extends A, E2>(refinement: Refinement<A, B>, onFalse: (a: A) => E2): <R, E1>(
    ma: ReaderEither<R, E1, A>
  ) => ReaderEither<R, E2 | E1, B>
  <A, E2>(predicate: Predicate<A>, onFalse: (a: A) => E2): <R, E1, B extends A>(
    mb: ReaderEither<R, E1, B>
  ) => ReaderEither<R, E2 | E1, B>
  <A, E2>(predicate: Predicate<A>, onFalse: (a: A) => E2): <R, E1>(
    ma: ReaderEither<R, E1, A>
  ) => ReaderEither<R, E2 | E1, A>
}

Added in v2.9.0

getCompactable

Signature

export declare const getCompactable: <E>(M: Monoid<E>) => Compactable3C<'ReaderEither', E>

Added in v2.10.0

getFilterable

Signature

export declare function getFilterable<E>(M: Monoid<E>): Filterable3C<URI, E>

Added in v2.10.0

instances

Alt

Signature

export declare const Alt: Alt3<'ReaderEither'>

Added in v2.7.0

Applicative

Signature

export declare const Applicative: Applicative3<'ReaderEither'>

Added in v2.7.0

Apply

Signature

export declare const Apply: Apply3<'ReaderEither'>

Added in v2.10.0

Bifunctor

Signature

export declare const Bifunctor: Bifunctor3<'ReaderEither'>

Added in v2.7.0

Chain

Signature

export declare const Chain: chainable.Chain3<'ReaderEither'>

Added in v2.10.0

FromEither

Signature

export declare const FromEither: FromEither3<'ReaderEither'>

Added in v2.10.0

FromReader

Signature

export declare const FromReader: FromReader3<'ReaderEither'>

Added in v2.11.0

Functor

Signature

export declare const Functor: Functor3<'ReaderEither'>

Added in v2.7.0

Monad

Signature

export declare const Monad: Monad3<'ReaderEither'>

Added in v2.7.0

MonadThrow

Signature

export declare const MonadThrow: MonadThrow3<'ReaderEither'>

Added in v2.7.0

Pointed

Signature

export declare const Pointed: Pointed3<'ReaderEither'>

Added in v2.10.0

legacy

bimap

Alias of mapBoth.

Signature

export declare const bimap: <E, G, A, B>(
  f: (e: E) => G,
  g: (a: A) => B
) => <R>(fa: ReaderEither<R, E, A>) => ReaderEither<R, G, B>

Added in v2.0.0

chain

Alias of flatMap.

Signature

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

Added in v2.0.0

chainEitherK

Alias of flatMapEither.

Signature

export declare const chainEitherK: <E, A, B>(
  f: (a: A) => E.Either<E, B>
) => <R>(ma: ReaderEither<R, E, A>) => ReaderEither<R, E, B>

Added in v2.4.0

chainEitherKW

Alias of flatMapEither.

Signature

export declare const chainEitherKW: <E2, A, B>(
  f: (a: A) => E.Either<E2, B>
) => <R, E1>(ma: ReaderEither<R, E1, A>) => ReaderEither<R, E2 | E1, B>

Added in v2.6.1

chainFirst

Alias of tap.

Signature

export declare const chainFirst: <R, E, A, B>(
  f: (a: A) => ReaderEither<R, E, B>
) => (ma: ReaderEither<R, E, A>) => ReaderEither<R, E, A>

Added in v2.0.0

chainFirstEitherK

Alias of tapEither.

Signature

export declare const chainFirstEitherK: <A, E, B>(
  f: (a: A) => E.Either<E, B>
) => <R>(ma: ReaderEither<R, E, A>) => ReaderEither<R, E, A>

Added in v2.12.0

chainFirstEitherKW

Alias of tapEither.

Less strict version of chainFirstEitherK.

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

Signature

export declare const chainFirstEitherKW: <A, E2, B>(
  f: (a: A) => E.Either<E2, B>
) => <R, E1>(ma: ReaderEither<R, E1, A>) => ReaderEither<R, E2 | E1, A>

Added in v2.12.0

chainFirstReaderK

Alias of tapReader.

Signature

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

Added in v2.11.0

chainFirstReaderKW

Alias of tapReader.

Less strict version of chainReaderK.

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, E>(ma: ReaderEither<R2, E, A>) => ReaderEither<R1 & R2, E, A>

Added in v2.11.0

chainFirstW

Alias of tap.

Signature

export declare const chainFirstW: <R2, E2, A, B>(
  f: (a: A) => ReaderEither<R2, E2, B>
) => <R1, E1>(ma: ReaderEither<R1, E1, A>) => ReaderEither<R1 & R2, E2 | E1, A>

Added in v2.8.0

chainOptionK

Use flatMapOption.

Signature

export declare const chainOptionK: <E>(
  onNone: LazyArg<E>
) => <A, B>(f: (a: A) => Option<B>) => <R>(ma: ReaderEither<R, E, A>) => ReaderEither<R, E, B>

Added in v2.10.0

chainOptionKW

Use flatMapOption.

Signature

export declare const chainOptionKW: <E2>(
  onNone: LazyArg<E2>
) => <A, B>(f: (a: A) => Option<B>) => <R, E1>(ma: ReaderEither<R, E1, A>) => ReaderEither<R, E2 | E1, B>

Added in v2.13.2

chainReaderK

Alias of flatMapReader.

Signature

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

Added in v2.11.0

chainW

Alias of flatMap.

Signature

export declare const chainW: <R2, E2, A, B>(
  f: (a: A) => ReaderEither<R2, E2, B>
) => <R1, E1>(ma: ReaderEither<R1, E1, A>) => ReaderEither<R1 & R2, E2 | E1, B>

Added in v2.6.0

fromOptionK

Use liftOption.

Signature

export declare const fromOptionK: <E>(
  onNone: LazyArg<E>
) => <A extends readonly unknown[], B>(f: (...a: A) => Option<B>) => <R = unknown>(...a: A) => ReaderEither<R, E, B>

Added in v2.10.0

mapLeft

Alias of mapError.

Signature

export declare const mapLeft: <E, G>(f: (e: E) => G) => <R, A>(fa: ReaderEither<R, E, A>) => ReaderEither<R, G, A>

Added in v2.0.0

orElseFirst

Alias of tapError.

Signature

export declare const orElseFirst: <E, R, B>(
  onLeft: (e: E) => ReaderEither<R, E, B>
) => <A>(ma: ReaderEither<R, E, A>) => ReaderEither<R, E, A>

Added in v2.11.0

orElseFirstW

Alias of tapError.

Signature

export declare const orElseFirstW: <E1, R2, E2, B>(
  onLeft: (e: E1) => ReaderEither<R2, E2, B>
) => <R1, A>(ma: ReaderEither<R1, E1, A>) => ReaderEither<R1 & R2, E1 | E2, A>

Added in v2.11.0

lifting

fromEitherK

Signature

export declare const fromEitherK: <E, A extends readonly unknown[], B>(
  f: (...a: A) => E.Either<E, B>
) => <R = unknown>(...a: A) => ReaderEither<R, E, B>

Added in v2.4.0

fromPredicate

Signature

export declare const fromPredicate: {
  <E, A, B extends A>(refinement: Refinement<A, B>, onFalse: (a: A) => E): <R = unknown>(a: A) => ReaderEither<R, E, B>
  <E, A>(predicate: Predicate<A>, onFalse: (a: A) => E): <R = unknown, B extends A = A>(b: B) => ReaderEither<R, E, B>
  <E, A>(predicate: Predicate<A>, onFalse: (a: A) => E): <R = unknown>(a: A) => ReaderEither<R, E, A>
}

Added in v2.0.0

fromReaderK

Signature

export declare const fromReaderK: <A extends readonly unknown[], R, B>(
  f: (...a: A) => R.Reader<R, B>
) => <E = never>(...a: A) => ReaderEither<R, E, B>

Added in v2.11.0

liftNullable

Signature

export declare const liftNullable: <A extends readonly unknown[], B, E>(
  f: (...a: A) => B | null | undefined,
  onNullable: (...a: A) => E
) => <R>(...a: A) => ReaderEither<R, E, NonNullable<B>>

Added in v2.15.0

liftOption

Signature

export declare const liftOption: <A extends readonly unknown[], B, E>(
  f: (...a: A) => Option<B>,
  onNone: (...a: A) => E
) => <R>(...a: A) => ReaderEither<R, E, B>

Added in v2.15.0

mapping

as

Maps the Right value of this ReaderEither to the specified constant value.

Signature

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

Added in v2.16.0

asUnit

Maps the Right value of this ReaderEither to the void constant value.

Signature

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

Added in v2.16.0

flap

Signature

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

Added in v2.0.0

model

ReaderEither (interface)

Signature

export interface ReaderEither<R, E, A> extends Reader<R, Either<E, A>> {}

Added in v2.0.0

pattern matching

fold

Alias of matchE.

Signature

export declare const fold: <R, E, A, B>(
  onLeft: (e: E) => R.Reader<R, B>,
  onRight: (a: A) => R.Reader<R, B>
) => (ma: ReaderEither<R, E, A>) => R.Reader<R, B>

Added in v2.0.0

foldW

Alias of matchEW.

Signature

export declare const foldW: <E, R2, B, A, R3, C>(
  onLeft: (e: E) => R.Reader<R2, B>,
  onRight: (a: A) => R.Reader<R3, C>
) => <R1>(ma: ReaderEither<R1, E, A>) => R.Reader<R1 & R2 & R3, B | C>

Added in v2.10.0

match

Signature

export declare const match: <E, B, A>(
  onLeft: (e: E) => B,
  onRight: (a: A) => B
) => <R>(ma: ReaderEither<R, E, A>) => R.Reader<R, B>

Added in v2.10.0

matchE

The E suffix (short for Effect) means that the handlers return an effect (Reader).

Signature

export declare const matchE: <R, E, A, B>(
  onLeft: (e: E) => R.Reader<R, B>,
  onRight: (a: A) => R.Reader<R, B>
) => (ma: ReaderEither<R, E, A>) => R.Reader<R, B>

Added in v2.10.0

matchEW

Less strict version of matchE.

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

Signature

export declare const matchEW: <E, R2, B, A, R3, C>(
  onLeft: (e: E) => R.Reader<R2, B>,
  onRight: (a: A) => R.Reader<R3, C>
) => <R1>(ma: ReaderEither<R1, E, A>) => R.Reader<R1 & R2 & R3, B | C>

Added in v2.10.0

matchW

Less strict version of match.

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

Signature

export declare const matchW: <E, B, A, C>(
  onLeft: (e: E) => B,
  onRight: (a: A) => C
) => <R>(ma: R.Reader<R, E.Either<E, A>>) => R.Reader<R, B | C>

Added in v2.10.0

sequencing

flatMap

Signature

export declare const flatMap: {
  <A, R2, E2, B>(f: (a: A) => ReaderEither<R2, E2, B>): <R1, E1>(
    ma: ReaderEither<R1, E1, A>
  ) => ReaderEither<R1 & R2, E2 | E1, B>
  <R1, E1, A, R2, E2, B>(ma: ReaderEither<R1, E1, A>, f: (a: A) => ReaderEither<R2, E2, B>): ReaderEither<
    R1 & R2,
    E1 | E2,
    B
  >
}

Added in v2.14.0

flatMapEither

Signature

export declare const flatMapEither: {
  <A, E2, B>(f: (a: A) => E.Either<E2, B>): <R, E1>(self: ReaderEither<R, E1, A>) => ReaderEither<R, E2 | E1, B>
  <R, E1, A, E2, B>(self: ReaderEither<R, E1, A>, f: (a: A) => E.Either<E2, B>): ReaderEither<R, E1 | E2, B>
}

Added in v2.15.0

flatMapNullable

Signature

export declare const flatMapNullable: {
  <A, B, E2>(f: (a: A) => B | null | undefined, onNullable: (a: A) => E2): <R, E1>(
    self: ReaderEither<R, E1, A>
  ) => ReaderEither<R, E2 | E1, NonNullable<B>>
  <R, E1, A, B, E2>(
    self: ReaderEither<R, E1, A>,
    f: (a: A) => B | null | undefined,
    onNullable: (a: A) => E2
  ): ReaderEither<R, E1 | E2, NonNullable<B>>
}

Added in v2.15.0

flatMapOption

Signature

export declare const flatMapOption: {
  <A, B, E2>(f: (a: A) => Option<B>, onNone: (a: A) => E2): <R, E1>(
    self: ReaderEither<R, E1, A>
  ) => ReaderEither<R, E2 | E1, B>
  <R, E1, A, B, E2>(self: ReaderEither<R, E1, A>, f: (a: A) => Option<B>, onNone: (a: A) => E2): ReaderEither<
    R,
    E1 | E2,
    B
  >
}

Added in v2.15.0

flatMapReader

Signature

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

Added in v2.16.0

flatten

Signature

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

Added in v2.0.0

flattenW

Less strict version of flatten.

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

Signature

export declare const flattenW: <R1, R2, E1, E2, A>(
  mma: ReaderEither<R1, E1, ReaderEither<R2, E2, A>>
) => ReaderEither<R1 & R2, E1 | E2, A>

Added in v2.11.0

traversing

sequenceArray

Equivalent to ReadonlyArray#sequence(Applicative).

Signature

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

Added in v2.9.0

traverseArray

Equivalent to ReadonlyArray#traverse(Applicative).

Signature

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

Added in v2.9.0

traverseArrayWithIndex

Equivalent to ReadonlyArray#traverseWithIndex(Applicative).

Signature

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

Added in v2.9.0

traverseReadonlyArrayWithIndex

Equivalent to ReadonlyArray#traverseWithIndex(Applicative).

Signature

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

Added in v2.11.0

traverseReadonlyNonEmptyArrayWithIndex

Equivalent to ReadonlyNonEmptyArray#traverseWithIndex(Applicative).

Signature

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

Added in v2.11.0

type lambdas

URI

Signature

export declare const URI: 'ReaderEither'

Added in v2.0.0

URI (type alias)

Signature

export type URI = typeof URI

Added in v2.0.0

utils

ApT

Signature

export declare const ApT: ReaderEither<unknown, never, readonly []>

Added in v2.11.0

ap

Signature

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

Added in v2.0.0

apFirst

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

Signature

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

Added in v2.0.0

apFirstW

Less strict version of apFirst

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

Signature

export declare const apFirstW: <R2, E2, B>(
  second: ReaderEither<R2, E2, B>
) => <R1, E1, A>(first: ReaderEither<R1, E1, A>) => ReaderEither<R1 & R2, E2 | E1, A>

Added in v2.12.0

apSecond

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

Signature

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

Added in v2.0.0

apSecondW

Less strict version of apSecond

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

Signature

export declare const apSecondW: <R2, E2, B>(
  second: ReaderEither<R2, E2, B>
) => <R1, E1, A>(first: ReaderEither<R1, E1, A>) => ReaderEither<R1 & R2, E2 | E1, B>

Added in v2.12.0

apW

Less strict version of ap.

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

Signature

export declare const apW: <R2, E2, A>(
  fa: ReaderEither<R2, E2, A>
) => <R1, E1, B>(fab: ReaderEither<R1, E1, (a: A) => B>) => ReaderEither<R1 & R2, E2 | E1, 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) => <E, A>(ma: ReaderEither<R1, E, A>) => ReaderEither<R2, E, A>

Added in v2.0.0

swap

Signature

export declare const swap: <R, E, A>(ma: ReaderEither<R, E, A>) => ReaderEither<R, A, E>

Added in v2.0.0

throwError

Signature

export declare const throwError: <R, E, A>(e: E) => ReaderEither<R, E, A>

Added in v2.7.0

zone of death

getApplyMonoid

Use getApplicativeMonoid instead.

Signature

export declare const getApplyMonoid: <R, E, A>(M: Monoid<A>) => Monoid<ReaderEither<R, E, A>>

Added in v2.0.0

getApplySemigroup

Use getApplySemigroup instead.

Signature

export declare const getApplySemigroup: <R, E, A>(S: Semigroup<A>) => Semigroup<ReaderEither<R, E, A>>

Added in v2.0.0

getReaderValidation

Use getApplicativeReaderValidation and getAltReaderValidation instead.

Signature

export declare function getReaderValidation<E>(
  SE: Semigroup<E>
): Monad3C<URI, E> & Bifunctor3<URI> & Alt3C<URI, E> & MonadThrow3C<URI, E>

Added in v2.3.0

getSemigroup

Use getApplySemigroup instead.

Signature

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

Added in v2.0.0

readerEither

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

Signature

export declare const readerEither: Monad3<'ReaderEither'> &
  Bifunctor3<'ReaderEither'> &
  Alt3<'ReaderEither'> &
  MonadThrow3<'ReaderEither'>

Added in v2.0.0