@typed/fp
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Data Structures and Resources for fp-ts
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---
title: ReaderOption.ts
nav_order: 44
parent: Modules
---
## ReaderOption overview
ReaderOption is an OptionT of fp-ts/Reader
Added in v0.9.2
---
<h2 class="text-delta">Table of contents</h2>
- [Combinator](#combinator)
- [alt](#alt)
- [altW](#altw)
- [ap](#ap)
- [chain](#chain)
- [chainFirstReaderK](#chainfirstreaderk)
- [chainNullableK](#chainnullablek)
- [chainOptionK](#chainoptionk)
- [chainReaderK](#chainreaderk)
- [chainRec](#chainrec)
- [local](#local)
- [map](#map)
- [Constructor](#constructor)
- [altAll](#altall)
- [apFirst](#apfirst)
- [apFirstW](#apfirstw)
- [apS](#aps)
- [apSW](#apsw)
- [apSecond](#apsecond)
- [apSecondW](#apsecondw)
- [apT](#apt)
- [apTW](#aptw)
- [ask](#ask)
- [asks](#asks)
- [bind](#bind)
- [chainFirst](#chainfirst)
- [fromEither](#fromeither)
- [fromIO](#fromio)
- [fromNullable](#fromnullable)
- [fromNullableK](#fromnullablek)
- [fromOptionK](#fromoptionk)
- [fromPredicate](#frompredicate)
- [fromReader](#fromreader)
- [fromReaderK](#fromreaderk)
- [some](#some)
- [zero](#zero)
- [Deconsructor](#deconsructor)
- [getOrElseE](#getorelsee)
- [Deconstructor](#deconstructor)
- [getOrElse](#getorelse)
- [getOrElseEW](#getorelseew)
- [getOrElseW](#getorelsew)
- [match](#match)
- [matchE](#matche)
- [matchEW](#matchew)
- [Instance](#instance)
- [Alt](#alt)
- [Alternative](#alternative)
- [Applicative](#applicative)
- [Apply](#apply)
- [Chain](#chain)
- [ChainRec](#chainrec)
- [FromIO](#fromio)
- [FromReader](#fromreader)
- [Functor](#functor)
- [Monad](#monad)
- [MonadRec](#monadrec)
- [Pointed](#pointed)
- [Provide](#provide)
- [ProvideAll](#provideall)
- [ProvideSome](#providesome)
- [UseAll](#useall)
- [UseSome](#usesome)
- [Model](#model)
- [ReaderOption (interface)](#readeroption-interface)
- [Typeclass Instance](#typeclass-instance)
- [getApplySemigroup](#getapplysemigroup)
- [URI](#uri)
- [URI](#uri-1)
- [URI (type alias)](#uri-type-alias)
---
# Combinator
## alt
**Signature**
```ts
export declare const alt: <E, A>(
second: Lazy<R.Reader<E, O.Option<A>>>,
) => (first: R.Reader<E, O.Option<A>>) => R.Reader<E, O.Option<A>>
```
Added in v0.9.2
## altW
**Signature**
```ts
export declare const altW: <E1, A>(
second: Lazy<ReaderOption<E1, A>>,
) => <E2, B>(first: ReaderOption<E2, B>) => ReaderOption<E1 & E2, A | B>
```
Added in v0.9.2
## ap
**Signature**
```ts
export declare const ap: <E, A>(
fa: R.Reader<E, O.Option<A>>,
) => <B>(fab: R.Reader<E, O.Option<(a: A) => B>>) => R.Reader<E, O.Option<B>>
```
Added in v0.9.2
## chain
**Signature**
```ts
export declare const chain: <A, E, B>(
f: (a: A) => R.Reader<E, O.Option<B>>,
) => (ma: R.Reader<E, O.Option<A>>) => R.Reader<E, O.Option<B>>
```
Added in v0.9.2
## chainFirstReaderK
**Signature**
```ts
export declare const chainFirstReaderK: <A, R, B>(
f: (a: A) => R.Reader<R, B>,
) => (ma: ReaderOption<R, A>) => ReaderOption<R, A>
```
Added in v0.9.2
## chainNullableK
**Signature**
```ts
export declare const chainNullableK: <A, B>(
f: (a: A) => B | null | undefined,
) => <E>(ma: R.Reader<E, O.Option<A>>) => R.Reader<E, O.Option<NonNullable<B>>>
```
Added in v0.9.2
## chainOptionK
**Signature**
```ts
export declare const chainOptionK: <A, B>(
f: (a: A) => O.Option<B>,
) => <E>(ma: R.Reader<E, O.Option<A>>) => R.Reader<E, O.Option<B>>
```
Added in v0.9.2
## chainReaderK
**Signature**
```ts
export declare const chainReaderK: <A, R, B>(
f: (a: A) => R.Reader<R, B>,
) => (ma: ReaderOption<R, A>) => ReaderOption<R, B>
```
Added in v0.9.2
## chainRec
**Signature**
```ts
export declare const chainRec: <A, E, B>(
f: (value: A) => ReaderOption<E, Ei.Either<A, B>>,
) => (value: A) => ReaderOption<E, B>
```
Added in v0.9.2
## local
**Signature**
```ts
export declare const local: <A, B>(
f: (a: A) => B,
) => <C>(ro: ReaderOption<B, C>) => ReaderOption<A, C>
```
Added in v0.9.2
## map
**Signature**
```ts
export declare const map: <A, B>(
f: (a: A) => B,
) => <E>(fa: R.Reader<E, O.Option<A>>) => R.Reader<E, O.Option<B>>
```
Added in v0.9.2
# Constructor
## altAll
**Signature**
```ts
export declare const altAll: <E, A>(
startWith: ReaderOption<E, A>,
) => (as: readonly ReaderOption<E, A>[]) => ReaderOption<E, A>
```
Added in v0.12.2
## apFirst
**Signature**
```ts
export declare const apFirst: <E, B>(
second: ReaderOption<E, B>,
) => <A>(first: ReaderOption<E, A>) => ReaderOption<E, A>
```
Added in v0.12.2
## apFirstW
**Signature**
```ts
export declare const apFirstW: <E1, B>(
second: ReaderOption<E1, B>,
) => <E2, A>(first: ReaderOption<E2, A>) => ReaderOption<E1 & E2, A>
```
Added in v0.12.2
## apS
**Signature**
```ts
export declare const apS: <N, A, E, B>(
name: Exclude<N, keyof A>,
fb: ReaderOption<E, B>,
) => (
fa: ReaderOption<E, A>,
) => ReaderOption<E, { readonly [K in N | keyof A]: K extends keyof A ? A[K] : B }>
```
Added in v0.12.2
## apSW
**Signature**
```ts
export declare const apSW: <N extends string, A, E1, B>(
name: Exclude<N, keyof A>,
fb: ReaderOption<E1, B>,
) => <E2>(
fa: ReaderOption<E2, A>,
) => ReaderOption<E1 & E2, { readonly [K in N | keyof A]: K extends keyof A ? A[K] : B }>
```
Added in v0.12.2
## apSecond
**Signature**
```ts
export declare const apSecond: <E, B>(
second: ReaderOption<E, B>,
) => <A>(first: ReaderOption<E, A>) => ReaderOption<E, B>
```
Added in v0.12.2
## apSecondW
**Signature**
```ts
export declare const apSecondW: <E1, B>(
second: ReaderOption<E1, B>,
) => <E2, A>(first: ReaderOption<E2, A>) => ReaderOption<E1 & E2, B>
```
Added in v0.12.2
## apT
**Signature**
```ts
export declare const apT: <E, B>(
fb: ReaderOption<E, B>,
) => <A>(fas: ReaderOption<E, A>) => ReaderOption<E, readonly [...A, B]>
```
Added in v0.12.2
## apTW
**Signature**
```ts
export declare const apTW: <E1, B>(
fb: ReaderOption<E1, B>,
) => <E2, A extends readonly unknown[]>(
fas: ReaderOption<E2, A>,
) => ReaderOption<E1 & E2, readonly [...A, B]>
```
Added in v0.12.2
## ask
**Signature**
```ts
export declare const ask: <R>() => ReaderOption<R, R>
```
Added in v0.9.2
## asks
**Signature**
```ts
export declare const asks: <R, A>(f: (r: R) => A) => ReaderOption<R, A>
```
Added in v0.9.2
## bind
**Signature**
```ts
export declare const bind: <N, A, E, B>(
name: Exclude<N, keyof A>,
f: (a: A) => ReaderOption<E, B>,
) => (
ma: ReaderOption<E, A>,
) => ReaderOption<E, { readonly [K in N | keyof A]: K extends keyof A ? A[K] : B }>
```
Added in v0.12.2
## chainFirst
**Signature**
```ts
export declare const chainFirst: <A, E, B>(
f: (a: A) => ReaderOption<E, B>,
) => (first: ReaderOption<E, A>) => ReaderOption<E, A>
```
Added in v0.12.2
## fromEither
**Signature**
```ts
export declare const fromEither: <A, E>(e: Ei.Either<unknown, A>) => R.Reader<E, O.Option<A>>
```
Added in v0.9.2
## fromIO
**Signature**
```ts
export declare const fromIO: NaturalTransformation12<'IO', '@typed/fp/ReaderOption'>
```
Added in v0.9.2
## fromNullable
**Signature**
```ts
export declare const fromNullable: <A, E>(a: A) => R.Reader<E, O.Option<NonNullable<A>>>
```
Added in v0.9.2
## fromNullableK
**Signature**
```ts
export declare const fromNullableK: <A, B>(
f: (...a: A) => B | null | undefined,
) => <E>(...a: A) => R.Reader<E, O.Option<NonNullable<B>>>
```
Added in v0.9.2
## fromOptionK
**Signature**
```ts
export declare const fromOptionK: <A, B>(
f: (...a: A) => O.Option<B>,
) => <E>(...a: A) => R.Reader<E, O.Option<B>>
```
Added in v0.9.2
## fromPredicate
**Signature**
```ts
export declare const fromPredicate: {
<A, B>(refinement: Refinement<A, B>): <E>(a: A) => R.Reader<E, O.Option<B>>
<A>(predicate: Predicate<A>): <E, B>(b: B) => R.Reader<E, O.Option<B>>
}
```
Added in v0.9.2
## fromReader
**Signature**
```ts
export declare const fromReader: <E, A>(ma: R.Reader<E, A>) => R.Reader<E, O.Option<A>>
```
Added in v0.9.2
## fromReaderK
**Signature**
```ts
export declare const fromReaderK: <A, R, B>(
f: (...a: A) => R.Reader<R, B>,
) => (...a: A) => ReaderOption<R, B>
```
Added in v0.9.2
## some
**Signature**
```ts
export declare const some: <A, E>(a: A) => R.Reader<E, O.Option<A>>
```
Added in v0.9.2
## zero
**Signature**
```ts
export declare const zero: <E, A>() => R.Reader<E, O.Option<A>>
```
Added in v0.9.2
# Deconsructor
## getOrElseE
**Signature**
```ts
export declare const getOrElseE: <E, A>(
onNone: Lazy<R.Reader<E, A>>,
) => (fa: R.Reader<E, O.Option<A>>) => R.Reader<E, A>
```
Added in v0.9.2
# Deconstructor
## getOrElse
**Signature**
```ts
export declare const getOrElse: <A>(
onNone: Lazy<A>,
) => <E>(fa: R.Reader<E, O.Option<A>>) => R.Reader<E, A>
```
Added in v0.9.2
## getOrElseEW
**Signature**
```ts
export declare const getOrElseEW: <E1, A>(
onNone: Lazy<R.Reader<E1, A>>,
) => <E2, B>(fa: ReaderOption<E2, B>) => R.Reader<E1 & E2, A | B>
```
Added in v0.9.2
## getOrElseW
**Signature**
```ts
export declare const getOrElseW: <A>(
onNone: Lazy<A>,
) => <E, B>(fa: R.Reader<E, O.Option<B>>) => R.Reader<E, A | B>
```
Added in v0.13.0
## match
**Signature**
```ts
export declare const match: <B, A>(
onNone: () => B,
onSome: (a: A) => B,
) => <E>(ma: R.Reader<E, O.Option<A>>) => R.Reader<E, B>
```
Added in v0.9.2
## matchE
**Signature**
```ts
export declare const matchE: <E, B, A>(
onNone: () => R.Reader<E, B>,
onSome: (a: A) => R.Reader<E, B>,
) => (ma: R.Reader<E, O.Option<A>>) => R.Reader<E, B>
```
Added in v0.9.2
## matchEW
**Signature**
```ts
export declare const matchEW: <E1, B, A, E2, C>(
onNone: () => R.Reader<E1, B>,
onSome: (a: A) => R.Reader<E2, C>,
) => <E3>(ma: R.Reader<E3, O.Option<A>>) => R.Reader<E1 & E2 & E3, B | C>
```
Added in v0.13.0
# Instance
## Alt
**Signature**
```ts
export declare const Alt: Alt_.Alt2<'@typed/fp/ReaderOption'>
```
Added in v0.9.2
## Alternative
**Signature**
```ts
export declare const Alternative: Alternative2<'@typed/fp/ReaderOption'>
```
Added in v0.9.2
## Applicative
**Signature**
```ts
export declare const Applicative: Applicative2<'@typed/fp/ReaderOption'>
```
Added in v0.9.2
## Apply
**Signature**
```ts
export declare const Apply: Ap.Apply2<'@typed/fp/ReaderOption'>
```
Added in v0.9.2
## Chain
**Signature**
```ts
export declare const Chain: CH.Chain2<'@typed/fp/ReaderOption'>
```
Added in v0.9.2
## ChainRec
**Signature**
```ts
export declare const ChainRec: ChainRec2<'@typed/fp/ReaderOption'>
```
Added in v0.9.2
## FromIO
**Signature**
```ts
export declare const FromIO: FromIO2<'@typed/fp/ReaderOption'>
```
Added in v0.9.2
## FromReader
**Signature**
```ts
export declare const FromReader: FR.FromReader2<'@typed/fp/ReaderOption'>
```
Added in v0.9.2
## Functor
**Signature**
```ts
export declare const Functor: Functor2<'@typed/fp/ReaderOption'>
```
Added in v0.9.2
## Monad
**Signature**
```ts
export declare const Monad: Monad2<'@typed/fp/ReaderOption'>
```
Added in v0.9.2
## MonadRec
**Signature**
```ts
export declare const MonadRec: MonadRec2<'@typed/fp/ReaderOption'>
```
Added in v0.9.2
## Pointed
**Signature**
```ts
export declare const Pointed: Pointed2<'@typed/fp/ReaderOption'>
```
Added in v0.9.2
## Provide
**Signature**
```ts
export declare const Provide: Provide2<'@typed/fp/ReaderOption'>
```
Added in v0.9.2
## ProvideAll
**Signature**
```ts
export declare const ProvideAll: ProvideAll2<'@typed/fp/ReaderOption'>
```
Added in v0.9.2
## ProvideSome
**Signature**
```ts
export declare const ProvideSome: ProvideSome2<'@typed/fp/ReaderOption'>
```
Added in v0.9.2
## UseAll
**Signature**
```ts
export declare const UseAll: UseAll2<'@typed/fp/ReaderOption'>
```
Added in v0.9.2
## UseSome
**Signature**
```ts
export declare const UseSome: UseSome2<'@typed/fp/ReaderOption'>
```
Added in v0.9.2
# Model
## ReaderOption (interface)
**Signature**
```ts
export interface ReaderOption<E, A> extends R.Reader<E, O.Option<A>> {}
```
Added in v0.9.2
# Typeclass Instance
## getApplySemigroup
**Signature**
```ts
export declare const getApplySemigroup: <A, E>(S: Semigroup<A>) => Semigroup<ReaderOption<E, A>>
```
Added in v0.12.2
# URI
## URI
**Signature**
```ts
export declare const URI: '@typed/fp/ReaderOption'
```
Added in v0.9.2
## URI (type alias)
**Signature**
```ts
export type URI = typeof URI
```
Added in v0.9.2