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fp-ts

IOOption overview

IOOption<A> represents a synchronous computation that either yields a value of type A or nothing.

If you want to represent a synchronous computation that never fails, please see IO. If you want to represent a synchronous computation that may fail, please see IOEither.

Added in v2.12.0

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: {
  <A, _>(self: IOOption<A>, f: (a: A) => IOOption<_>): IOOption<A>
  <A, _>(f: (a: A) => IOOption<_>): (self: IOOption<A>) => IOOption<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, E, _>(f: (a: A) => Either<E, _>): (self: IOOption<A>) => IOOption<A>
  <A, E, _>(self: IOOption<A>, f: (a: A) => Either<E, _>): IOOption<A>
}

Example

import { pipe } from 'fp-ts/function'
import * as IOO from 'fp-ts/IOOption'
import * as O from 'fp-ts/Option'
import * as E from 'fp-ts/Either'

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

assert.deepStrictEqual(compute(1)(), O.of(1))
assert.deepStrictEqual(compute(-1)(), O.none)

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

Example

import { pipe } from 'fp-ts/function'
import * as IOO from 'fp-ts/IOOption'
import * as O from 'fp-ts/Option'
import * as Console from 'fp-ts/Console'

// Will produce `Hello, fp-ts` to the stdout
const effectA = pipe(
  IOO.of('fp-ts'),
  IOO.tapIO((value) => Console.log(`Hello, ${value}`))
)

// No output to the stdout
const effectB = pipe(
  IOO.none as IOO.IOOption<string>,
  IOO.tapIO((value) => Console.log(`Hello, ${value}`))
)

async function test() {
  assert.deepStrictEqual(effectA(), O.of('fp-ts'))
  assert.deepStrictEqual(effectB(), O.none)
}

test()

Added in v2.16.0

constructors

none

Signature

export declare const none: IOOption<never>

Added in v2.12.0

of

Signature

export declare const of: <A>(a: A) => IOOption<A>

Added in v2.12.0

some

Signature

export declare const some: <A>(a: A) => IOOption<A>

Added in v2.12.0

conversions

fromEither

Signature

export declare const fromEither: <A>(fa: Either<unknown, A>) => IOOption<A>

Added in v2.12.0

fromIO

Signature

export declare const fromIO: <A>(fa: I.IO<A>) => IOOption<A>

Added in v2.12.0

fromIOEither

Signature

export declare const fromIOEither: <A>(fa: IOEither<unknown, A>) => IOOption<A>

Added in v2.12.0

fromNullable

Signature

export declare const fromNullable: <A>(a: A) => IOOption<NonNullable<A>>

Added in v2.12.0

fromOption

Signature

export declare const fromOption: <A>(fa: O.Option<A>) => IOOption<A>

Added in v2.12.0

toNullable

Signature

export declare const toNullable: <A>(ma: IOOption<A>) => I.IO<A | null>

Added in v2.12.0

toUndefined

Signature

export declare const toUndefined: <A>(ma: IOOption<A>) => I.IO<A | undefined>

Added in v2.12.0

do notation

Do

Signature

export declare const Do: IOOption<{}>

Added in v2.12.0

apS

Signature

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

Added in v2.12.0

bind

Signature

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

Added in v2.12.0

bindTo

Signature

export declare const bindTo: <N>(name: N) => <A>(fa: IOOption<A>) => IOOption<{ readonly [K in N]: A }>

Added in v2.12.0

guard

Signature

export declare const guard: (b: boolean) => IOOption<void>

Added in v2.12.0

let

Signature

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

Added in v2.13.0

error handling

alt

Signature

export declare const alt: <A>(second: LazyArg<IOOption<A>>) => (first: IOOption<A>) => IOOption<A>

Added in v2.12.0

altW

Less strict version of alt.

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

Signature

export declare const altW: <B>(second: LazyArg<IOOption<B>>) => <A>(first: IOOption<A>) => IOOption<B | A>

Added in v2.12.0

getOrElse

Signature

export declare const getOrElse: <A>(onNone: LazyArg<I.IO<A>>) => (fa: IOOption<A>) => I.IO<A>

Added in v2.12.0

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: <B>(onNone: LazyArg<I.IO<B>>) => <A>(ma: IOOption<A>) => I.IO<B | A>

Added in v2.12.0

filtering

compact

Signature

export declare const compact: <A>(fa: IOOption<O.Option<A>>) => IOOption<A>

Added in v2.12.0

filter

Signature

export declare const filter: {
  <A, B extends A>(refinement: Refinement<A, B>): (fb: IOOption<A>) => IOOption<B>
  <A>(predicate: Predicate<A>): <B extends A>(fb: IOOption<B>) => IOOption<B>
  <A>(predicate: Predicate<A>): (fa: IOOption<A>) => IOOption<A>
}

Added in v2.12.0

filterMap

Signature

export declare const filterMap: <A, B>(f: (a: A) => O.Option<B>) => (fga: IOOption<A>) => IOOption<B>

Added in v2.12.0

partition

Signature

export declare const partition: {
  <A, B extends A>(refinement: Refinement<A, B>): (fb: IOOption<A>) => Separated<IOOption<A>, IOOption<B>>
  <A>(predicate: Predicate<A>): <B extends A>(fb: IOOption<B>) => Separated<IOOption<B>, IOOption<B>>
  <A>(predicate: Predicate<A>): (fa: IOOption<A>) => Separated<IOOption<A>, IOOption<A>>
}

Added in v2.12.0

partitionMap

Signature

export declare const partitionMap: <A, B, C>(
  f: (a: A) => Either<B, C>
) => (fa: IOOption<A>) => Separated<IOOption<B>, IOOption<C>>

Added in v2.12.0

separate

Signature

export declare const separate: <A, B>(fa: IOOption<Either<A, B>>) => Separated<IOOption<A>, IOOption<B>>

Added in v2.12.0

instances

Alt

Signature

export declare const Alt: Alt1<'IOOption'>

Added in v2.12.0

Alternative

Signature

export declare const Alternative: Alternative1<'IOOption'>

Added in v2.12.0

Applicative

Signature

export declare const Applicative: Applicative1<'IOOption'>

Added in v2.12.0

Apply

Signature

export declare const Apply: Apply1<'IOOption'>

Added in v2.12.0

Chain

Signature

export declare const Chain: chainable.Chain1<'IOOption'>

Added in v2.12.0

Compactable

Signature

export declare const Compactable: Compactable1<'IOOption'>

Added in v2.12.0

Filterable

Signature

export declare const Filterable: Filterable1<'IOOption'>

Added in v2.12.0

FromEither

Signature

export declare const FromEither: FromEither1<'IOOption'>

Added in v2.12.0

FromIO

Signature

export declare const FromIO: FromIO1<'IOOption'>

Added in v2.12.0

Functor

Signature

export declare const Functor: Functor1<'IOOption'>

Added in v2.12.0

Monad

Signature

export declare const Monad: Monad1<'IOOption'>

Added in v2.12.0

MonadIO

Signature

export declare const MonadIO: MonadIO1<'IOOption'>

Added in v2.12.0

Pointed

Signature

export declare const Pointed: Pointed1<'IOOption'>

Added in v2.12.0

Zero

Signature

export declare const Zero: Zero1<'IOOption'>

Added in v2.12.0

legacy

chain

Alias of flatMap.

Signature

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

Added in v2.12.0

chainEitherK

Alias of flatMapEither.

Signature

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

Added in v2.12.0

chainFirst

Alias of tap.

Signature

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

Added in v2.12.0

chainFirstEitherK

Alias of tapEither.

Signature

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

Added in v2.12.0

chainFirstIOK

Alias of tapIO.

Signature

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

Added in v2.12.0

chainIOK

Alias of flatMapIO.

Signature

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

Added in v2.12.0

chainNullableK

Alias of flatMapNullable.

Signature

export declare const chainNullableK: <A, B>(
  f: (a: A) => B | null | undefined
) => (ma: IOOption<A>) => IOOption<NonNullable<B>>

Added in v2.12.0

chainOptionK

Alias of flatMapOption.

Signature

export declare const chainOptionK: <A, B>(f: (a: A) => O.Option<B>) => (ma: IOOption<A>) => IOOption<B>

Added in v2.12.0

lifting

fromEitherK

Signature

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

Added in v2.12.0

fromIOK

Signature

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

Added in v2.12.0

fromNullableK

Signature

export declare const fromNullableK: <A extends readonly unknown[], B>(
  f: (...a: A) => B | null | undefined
) => (...a: A) => IOOption<NonNullable<B>>

Added in v2.12.0

fromOptionK

Signature

export declare const fromOptionK: <A extends readonly unknown[], B>(
  f: (...a: A) => O.Option<B>
) => (...a: A) => IOOption<B>

Added in v2.12.0

fromPredicate

Signature

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

Added in v2.12.0

mapping

as

Maps the Some value of this IOOption to the specified constant value.

Signature

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

Added in v2.16.0

asUnit

Maps the Some value of this IOOption to the void constant value.

Signature

export declare const asUnit: <_>(self: IOOption<_>) => IOOption<void>

Added in v2.16.0

flap

Signature

export declare const flap: <A>(a: A) => <B>(fab: IOOption<(a: A) => B>) => IOOption<B>

Added in v2.12.0

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) => (fa: IOOption<A>) => IOOption<B>

Added in v2.12.0

model

IOOption (interface)

Signature

export interface IOOption<A> extends IO<Option<A>> {}

Added in v2.12.0

pattern matching

fold

Alias of matchE.

Signature

export declare const fold: <B, A>(onNone: () => I.IO<B>, onSome: (a: A) => I.IO<B>) => (ma: IOOption<A>) => I.IO<B>

Added in v2.12.0

match

Signature

export declare const match: <B, A>(onNone: () => B, onSome: (a: A) => B) => (ma: IOOption<A>) => I.IO<B>

Added in v2.12.0

matchE

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

Signature

export declare const matchE: <B, A>(onNone: () => I.IO<B>, onSome: (a: A) => I.IO<B>) => (ma: IOOption<A>) => I.IO<B>

Added in v2.12.0

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: <B, C, A>(
  onNone: () => I.IO<B>,
  onSome: (a: A) => I.IO<C>
) => (ma: IOOption<A>) => I.IO<B | C>

Added in v2.12.0

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: <B, A, C>(onNone: () => B, onSome: (a: A) => C) => (ma: IOOption<A>) => I.IO<B | C>

Added in v2.12.0

sequencing

flatMap

Signature

export declare const flatMap: {
  <A, B>(f: (a: A) => IOOption<B>): (ma: IOOption<A>) => IOOption<B>
  <A, B>(ma: IOOption<A>, f: (a: A) => IOOption<B>): IOOption<B>
}

Added in v2.14.0

flatMapEither

Signature

export declare const flatMapEither: {
  <A, B, _>(f: (a: A) => Either<_, B>): (self: IOOption<A>) => IOOption<B>
  <A, B, _>(self: IOOption<A>, f: (a: A) => Either<_, B>): IOOption<B>
}

Added in v2.16.0

flatMapIO

Signature

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

Added in v2.16.0

flatMapNullable

Signature

export declare const flatMapNullable: {
  <A, B>(f: (a: A) => B | null | undefined): (self: IOOption<A>) => IOOption<B>
  <A, B>(self: IOOption<A>, f: (a: A) => B | null | undefined): IOOption<B>
}

Added in v2.16.0

flatMapOption

Signature

export declare const flatMapOption: {
  <A, B>(f: (a: A) => O.Option<B>): (self: IOOption<A>) => IOOption<B>
  <A, B>(self: IOOption<A>, f: (a: A) => O.Option<B>): IOOption<B>
}

Added in v2.16.0

flatten

Signature

export declare const flatten: <A>(mma: IOOption<IOOption<A>>) => IOOption<A>

Added in v2.12.0

traversing

traverseReadonlyArrayWithIndex

Equivalent to ReadonlyArray#traverseWithIndex(Applicative).

Signature

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

Added in v2.12.0

traverseReadonlyNonEmptyArrayWithIndex

Equivalent to ReadonlyNonEmptyArray#traverseWithIndex(Applicative).

Signature

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

Added in v2.12.0

type lambdas

URI

Signature

export declare const URI: 'IOOption'

Added in v2.12.0

URI (type alias)

Signature

export type URI = typeof URI

Added in v2.12.0

utils

ApT

Signature

export declare const ApT: IOOption<readonly []>

Added in v2.12.0

ap

Signature

export declare const ap: <A>(fa: IOOption<A>) => <B>(fab: IOOption<(a: A) => B>) => IOOption<B>

Added in v2.12.0

apFirst

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

Signature

export declare const apFirst: <B>(second: IOOption<B>) => <A>(first: IOOption<A>) => IOOption<A>

Added in v2.12.0

apSecond

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

Signature

export declare const apSecond: <B>(second: IOOption<B>) => <A>(first: IOOption<A>) => IOOption<B>

Added in v2.12.0

zero

Signature

export declare const zero: <A>() => IOOption<A>

Added in v2.12.0