IOEither overview

IOEither<E, A> represents a synchronous computation that either yields a value of type A or fails yielding an error of type E.

If you want to represent a synchronous computation that never fails, please see IO. If you want to represent a synchronous computation that may yield nothing, please see IOOption.

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

Example

import { pipe } from 'fp-ts/function'
import * as IOE from 'fp-ts/IOEither'
import * as E from 'fp-ts/Either'

const compute = (value: string) =>
  pipe(
    IOE.of(value),
    IOE.tapEither(() => (value.length > 0 ? E.right('ok') : E.left('error')))
  )

assert.deepStrictEqual(compute('')(), E.left('error'))
assert.deepStrictEqual(compute('fp-ts')(), E.right('fp-ts'))

Added in v2.16.0

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) => I.IO<_>): <E>(self: IOEither<E, A>) => IOEither<E, A>
  <E, A, _>(self: IOEither<E, A>, f: (a: A) => I.IO<_>): IOEither<E, A>
}

Example

import { pipe } from 'fp-ts/function'
import * as IOE from 'fp-ts/IOEither'
import * as E from 'fp-ts/Either'
import * as Console from 'fp-ts/Console'

const sayHello = (value: string) => Console.log(`Hello, ${value}`)

// Will produce `Hello, fp-ts` to the stdout
const effectA = IOE.tapIO(IOE.of('fp-ts'), sayHello)

// No output to the stdout
const effectB = pipe(IOE.left<string>('error'), IOE.tapIO(sayHello))

assert.deepStrictEqual(effectA(), E.right('fp-ts'))
assert.deepStrictEqual(effectB(), E.left('error'))

Added in v2.16.0

constructors

left

Signature

export declare const left: <E = never, A = never>(l: E) => IOEither<E, A>

Added in v2.0.0

leftIO

Signature

export declare const leftIO: <E = never, A = never>(me: I.IO<E>) => IOEither<E, A>

Added in v2.0.0

of

Signature

export declare const of: <E = never, A = never>(a: A) => IOEither<E, A>

Added in v2.8.5

Signature

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

Added in v2.0.0

rightIO

Signature

export declare const rightIO: <E = never, A = never>(ma: I.IO<A>) => IOEither<E, A>

Added in v2.0.0

conversions

fromEither

Signature

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

Added in v2.0.0

fromIO

Signature

export declare const fromIO: <A, E = never>(fa: I.IO<A>) => IOEither<E, A>

Added in v2.7.0

fromOption

Signature

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

Added in v2.0.0

toUnion

Signature

export declare const toUnion: <E, A>(fa: IOEither<E, A>) => I.IO<E | A>

Added in v2.10.0

do notation

Do

Signature

export declare const Do: IOEither<never, {}>

Added in v2.9.0

apS

Signature

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

Signature

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

Added in v2.8.0

bindW

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

Signature

export declare const bindW: <N extends string, A, E2, B>(
  name: Exclude<N, keyof A>,
  f: (a: A) => IOEither<E2, B>
) => <E1>(fa: IOEither<E1, A>) => IOEither<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
) => <E>(fa: IOEither<E, A>) => IOEither<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: <E, A>(that: LazyArg<IOEither<E, A>>) => (fa: IOEither<E, A>) => IOEither<E, A>

Added in v2.0.0

altW

Less strict version of alt.

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

Signature

export declare const altW: <E2, B>(
  that: LazyArg<IOEither<E2, B>>
) => <E1, A>(fa: IOEither<E1, A>) => IOEither<E2, B | A>

Added in v2.9.0

getAltIOValidation

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 getAltIOValidation<E>(S: Semigroup<E>): Alt2C<URI, E>

Added in v2.7.0

getApplicativeIOValidation

The default ApplicativePar 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 getApplicativeIOValidation<E>(S: Semigroup<E>): Applicative2C<URI, E>

Added in v2.7.0

getOrElse

Signature

export declare const getOrElse: <E, A>(onLeft: (e: E) => I.IO<A>) => (ma: IOEither<E, A>) => I.IO<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: <E, B>(onLeft: (e: E) => I.IO<B>) => <A>(ma: IOEither<E, A>) => I.IO<B | A>

Added in v2.6.0

mapBoth

Returns a IOEither 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): (self: IOEither<E, A>) => IOEither<G, B>
  <E, A, G, B>(self: IOEither<E, A>, f: (e: E) => G, g: (a: A) => B): IOEither<G, B>
}

Example

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

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

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

Added in v2.16.0

mapError

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

Signature

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

Example

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

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

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

Added in v2.16.0

orElse

Signature

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

Added in v2.0.0

orElseFirstIOK

Signature

export declare const orElseFirstIOK: <E, B>(onLeft: (e: E) => I.IO<B>) => <A>(ma: IOEither<E, A>) => IOEither<E, A>

Added in v2.12.0

orElseW

Less strict version of orElse.

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

Signature

export declare const orElseW: <E1, E2, B>(
  onLeft: (e: E1) => IOEither<E2, B>
) => <A>(ma: IOEither<E1, A>) => IOEither<E2, B | A>

Added in v2.10.0

orLeft

Signature

export declare const orLeft: <E1, E2>(onLeft: (e: E1) => I.IO<E2>) => <A>(fa: IOEither<E1, A>) => IOEither<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, E2, _>(onLeft: (e: E1) => IOEither<E2, _>): <A>(self: IOEither<E1, A>) => IOEither<E1 | E2, A>
  <E1, A, E2, _>(self: IOEither<E1, A>, onLeft: (e: E1) => IOEither<E2, _>): IOEither<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): (ma: IOEither<E, A>) => IOEither<E, B>
  <E, A>(predicate: Predicate<A>, onFalse: (a: A) => E): <B extends A>(mb: IOEither<E, B>) => IOEither<E, B>
  <E, A>(predicate: Predicate<A>, onFalse: (a: A) => E): (ma: IOEither<E, A>) => IOEither<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): <E1>(
    ma: IOEither<E1, A>
  ) => IOEither<E2 | E1, B>
  <A, E2>(predicate: Predicate<A>, onFalse: (a: A) => E2): <E1, B extends A>(
    mb: IOEither<E1, B>
  ) => IOEither<E2 | E1, B>
  <A, E2>(predicate: Predicate<A>, onFalse: (a: A) => E2): <E1>(ma: IOEither<E1, A>) => IOEither<E2 | E1, A>
}

Added in v2.9.0

getCompactable

Signature

export declare const getCompactable: <E>(M: Monoid<E>) => Compactable2C<'IOEither', E>

Added in v2.10.0

getFilterable

Signature

export declare function getFilterable<E>(M: Monoid<E>): Filterable2C<URI, E>

Added in v2.1.0

instances

Alt

Signature

export declare const Alt: Alt2<'IOEither'>

Added in v2.7.0

ApplicativePar

Runs computations in parallel.

Signature

export declare const ApplicativePar: Applicative2<'IOEither'>

Added in v2.8.4

ApplicativeSeq

Runs computations sequentially.

Signature

export declare const ApplicativeSeq: Applicative2<'IOEither'>

Added in v2.8.4

ApplyPar

Runs computations in parallel.

Signature

export declare const ApplyPar: Apply2<'IOEither'>

Added in v2.10.0

Bifunctor

Signature

export declare const Bifunctor: Bifunctor2<'IOEither'>

Added in v2.7.0

Chain

Signature

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

Added in v2.10.0

FromEither

Signature

export declare const FromEither: FromEither2<'IOEither'>

Added in v2.10.0

FromIO

Signature

export declare const FromIO: FromIO2<'IOEither'>

Added in v2.10.0

Functor

Signature

export declare const Functor: Functor2<'IOEither'>

Added in v2.7.0

Monad

Signature

export declare const Monad: Monad2<'IOEither'>

Added in v2.7.0

MonadIO

Signature

export declare const MonadIO: MonadIO2<'IOEither'>

Added in v2.7.0

MonadThrow

Signature

export declare const MonadThrow: MonadThrow2<'IOEither'>

Added in v2.7.0

Pointed

Signature

export declare const Pointed: Pointed2<'IOEither'>

Added in v2.10.0

interop

tryCatch

Constructs a new IOEither from a function that performs a side effect and might throw

See also tryCatchK.

Signature

export declare const tryCatch: <E, A>(f: LazyArg<A>, onThrow: (reason: unknown) => E) => IOEither<E, A>

Added in v2.0.0

tryCatchK

Converts a function that may throw to one returning a IOEither.

Signature

export declare const tryCatchK: <A extends readonly unknown[], B, E>(
  f: (...a: A) => B,
  onThrow: (reason: unknown) => E
) => (...a: A) => IOEither<E, B>

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) => (fa: IOEither<E, A>) => IOEither<G, B>

Added in v2.0.0

chain

Alias of flatMap.

Signature

export declare const chain: <E, A, B>(f: (a: A) => IOEither<E, B>) => (ma: IOEither<E, A>) => IOEither<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>) => (ma: IOEither<E, A>) => IOEither<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>
) => <E1>(ma: IOEither<E1, A>) => IOEither<E2 | E1, B>

Added in v2.6.1

chainFirst

Alias of tap.

Signature

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

Added in v2.12.0

chainFirstEitherKW

Alias of tapEither.

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

Signature

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

Added in v2.12.0

chainFirstIOK

Alias of tapIO.

Signature

export declare const chainFirstIOK: <A, B>(f: (a: A) => I.IO<B>) => <E>(first: IOEither<E, A>) => IOEither<E, A>

Added in v2.10.0

chainFirstW

Alias of tap.

Signature

export declare const chainFirstW: <E2, A, B>(
  f: (a: A) => IOEither<E2, B>
) => <E1>(ma: IOEither<E1, A>) => IOEither<E2 | E1, A>

Added in v2.8.0

chainIOK

Alias of flatMapIO.

Signature

export declare const chainIOK: <A, B>(f: (a: A) => I.IO<B>) => <E>(first: IOEither<E, A>) => IOEither<E, B>

Added in v2.10.0

chainOptionK

Use flatMapOption.

Signature

export declare const chainOptionK: <E>(
  onNone: LazyArg<E>
) => <A, B>(f: (a: A) => Option<B>) => (ma: IOEither<E, A>) => IOEither<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>) => <E1>(ma: IOEither<E1, A>) => IOEither<E2 | E1, B>

Added in v2.13.2

chainW

Alias of flatMap.

Signature

export declare const chainW: <E2, A, B>(
  f: (a: A) => IOEither<E2, B>
) => <E1>(ma: IOEither<E1, A>) => IOEither<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>) => (...a: A) => IOEither<E, B>

Added in v2.10.0

mapLeft

Alias of mapError.

Signature

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

Added in v2.0.0

orElseFirst

Alias of tapError.

Signature

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

Added in v2.11.0

orElseFirstW

Alias of tapError.

Signature

export declare const orElseFirstW: <E1, E2, B>(
  onLeft: (e: E1) => IOEither<E2, B>
) => <A>(ma: IOEither<E1, A>) => IOEither<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>
) => (...a: A) => IOEither<E, B>

Added in v2.4.0

fromIOK

Signature

export declare const fromIOK: <A extends readonly unknown[], B>(
  f: (...a: A) => I.IO<B>
) => <E = never>(...a: A) => IOEither<E, B>

Added in v2.10.0

fromPredicate

Signature

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

Added in v2.0.0

liftNullable

Signature

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

Added in v2.15.0

mapping

as

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

Signature

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

Added in v2.16.0

asUnit

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

Signature

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

Added in v2.16.0

flap

Signature

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

Added in v2.0.0

model

IOEither (interface)

Signature

export interface IOEither<E, A> extends IO<Either<E, A>> {}

Added in v2.0.0

pattern matching

fold

Alias of matchE.

Signature

export declare const fold: <E, A, B>(
  onLeft: (e: E) => I.IO<B>,
  onRight: (a: A) => I.IO<B>
) => (ma: IOEither<E, A>) => I.IO<B>

Added in v2.0.0

foldW

Alias of matchEW.

Signature

export declare const foldW: <E, B, A, C>(
  onLeft: (e: E) => I.IO<B>,
  onRight: (a: A) => I.IO<C>
) => (ma: IOEither<E, A>) => I.IO<B | C>

Added in v2.10.0

match

Signature

export declare const match: <E, B, A>(onLeft: (e: E) => B, onRight: (a: A) => B) => (ma: IOEither<E, A>) => I.IO<B>

Added in v2.10.0

matchE

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

Signature

export declare const matchE: <E, A, B>(
  onLeft: (e: E) => I.IO<B>,
  onRight: (a: A) => I.IO<B>
) => (ma: IOEither<E, A>) => I.IO<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, B, A, C>(
  onLeft: (e: E) => I.IO<B>,
  onRight: (a: A) => I.IO<C>
) => (ma: IOEither<E, A>) => I.IO<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
) => (ma: IOEither<E, A>) => I.IO<B | C>

Added in v2.10.0

sequencing

flatMap

Signature

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

Added in v2.14.0

flatMapEither

Signature

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

Added in v2.15.0

flatMapIO

Signature

export declare const flatMapIO: {
  <A, B>(f: (a: A) => I.IO<B>): <E>(self: IOEither<E, A>) => IOEither<E, B>
  <E, A, B>(self: IOEither<E, A>, f: (a: A) => I.IO<B>): IOEither<E, B>
}

Added in v2.16.0

flatMapNullable

Signature

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

Added in v2.15.0

flatten

Signature

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

Added in v2.0.0

flattenW

Less strict version of flatten.

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

Signature

export declare const flattenW: <E1, E2, A>(mma: IOEither<E1, IOEither<E2, A>>) => IOEither<E1 | E2, A>

Added in v2.11.0

traversing

sequenceArray

Equivalent to ReadonlyArray#sequence(Applicative).

Signature

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

Added in v2.9.0

sequenceSeqArray

Equivalent to ReadonlyArray#sequence(ApplicativeSeq).

Signature

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

Added in v2.9.0

traverseArray

Equivalent to ReadonlyArray#traverse(Applicative).

Signature

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

Added in v2.9.0

traverseArrayWithIndex

Equivalent to ReadonlyArray#traverseWithIndex(Applicative).

Signature

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

Added in v2.9.0

traverseReadonlyArrayWithIndex

Equivalent to ReadonlyArray#traverseWithIndex(ApplicativePar).

Signature

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

Added in v2.11.0

traverseReadonlyArrayWithIndexSeq

Equivalent to ReadonlyArray#traverseWithIndex(ApplicativeSeq).

Signature

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

Added in v2.11.0

traverseReadonlyNonEmptyArrayWithIndex

Equivalent to ReadonlyNonEmptyArray#traverseWithIndex(ApplicativePar).

Signature

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

Added in v2.11.0

traverseReadonlyNonEmptyArrayWithIndexSeq

Equivalent to ReadonlyNonEmptyArray#traverseWithIndex(ApplicativeSeq).

Signature

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

Added in v2.11.0

traverseSeqArray

Equivalent to ReadonlyArray#traverse(ApplicativeSeq).

Signature

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

Added in v2.9.0

traverseSeqArrayWithIndex

Equivalent to ReadonlyArray#traverseWithIndex(ApplicativeSeq).

Signature

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

Added in v2.9.0

type lambdas

URI

Signature

export declare const URI: 'IOEither'

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: IOEither<never, readonly []>

Added in v2.11.0

ap

Signature

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

Added in v2.0.0

apFirstW

Less strict version of apFirst.

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

Signature

export declare const apFirstW: <E2, B>(
  second: IOEither<E2, B>
) => <E1, A>(first: IOEither<E1, A>) => IOEither<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: <E, B>(second: IOEither<E, B>) => <A>(first: IOEither<E, A>) => IOEither<E, B>

Added in v2.0.0

apSecondW

Less strict version of apSecond.

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

Signature

export declare const apSecondW: <E2, B>(
  second: IOEither<E2, B>
) => <E1, A>(first: IOEither<E1, A>) => IOEither<E2 | E1, B>

Added in v2.12.0

apW

Less strict version of ap.

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

Signature

export declare const apW: <E2, A>(
  fa: IOEither<E2, A>
) => <E1, B>(fab: IOEither<E1, (a: A) => B>) => IOEither<E2 | E1, B>

Added in v2.8.0

bracket

Make sure that a resource is cleaned up in the event of an exception (*). The release action is called regardless of whether the body action throws (*) or returns.

(*) i.e. returns a Left

Signature

export declare const bracket: <E, A, B>(
  acquire: IOEither<E, A>,
  use: (a: A) => IOEither<E, B>,
  release: (a: A, e: E.Either<E, B>) => IOEither<E, void>
) => IOEither<E, B>

Added in v2.0.0

bracketW

Less strict version of bracket.

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

Signature

export declare const bracketW: <E1, A, E2, B, E3>(
  acquire: IOEither<E1, A>,
  use: (a: A) => IOEither<E2, B>,
  release: (a: A, e: E.Either<E2, B>) => IOEither<E3, void>
) => IOEither<E1 | E2 | E3, B>

Added in v2.12.0

swap

Signature

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

Added in v2.0.0

throwError

Signature

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

Added in v2.7.0

zone of death

Applicative

Use ApplicativePar instead

Signature

export declare const Applicative: Applicative2<'IOEither'>

Added in v2.7.0

getApplyMonoid

Use getApplicativeMonoid instead.

Signature

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

Added in v2.0.0

getApplySemigroup

Use getApplySemigroup instead.

Signature

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

Added in v2.0.0

getIOValidation

Use getApplicativeIOValidation and getAltIOValidation.

Signature

export declare function getIOValidation<E>(
  SE: Semigroup<E>
): Monad2C<URI, E> & Bifunctor2<URI> & Alt2C<URI, E> & MonadIO2C<URI, E> & MonadThrow2C<URI, E>

Added in v2.0.0

getSemigroup

Use getApplySemigroup instead.

Signature

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

Added in v2.0.0

ioEither

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

Signature

export declare const ioEither: Monad2<'IOEither'> &
  Bifunctor2<'IOEither'> &
  Alt2<'IOEither'> &
  MonadIO2<'IOEither'> &
  MonadThrow2<'IOEither'>

Added in v2.0.0