467 lines
13 KiB
TypeScript
467 lines
13 KiB
TypeScript
/**
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* The `Reader` monad (also called the Environment monad). Represents a computation, which can read values from a shared environment,
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* pass values from function to function, and execute sub-computations in a modified environment.
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* Using `Reader` monad for such computations is often clearer and easier than using the `State` monad.
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*
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* In this example the `Reader` monad provides access to variable bindings. `Bindings` are a map of `number` variables.
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* The variable count contains number of variables in the bindings. You can see how to run a `Reader` monad and retrieve
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* data from it, how to access the `Reader` data with `ask` and `asks`.
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*
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* @example
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* import { pipe } from 'fp-ts/function'
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* import * as O from 'fp-ts/Option'
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* import * as R from 'fp-ts/Reader'
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* import * as RR from 'fp-ts/ReadonlyRecord'
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*
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* interface Bindings extends RR.ReadonlyRecord<string, number> {}
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*
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* // The Reader monad, which implements this complicated check.
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* const isCountCorrect: R.Reader<Bindings, boolean> = pipe(
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* R.Do,
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* R.bind('count', () => R.asks(lookupVar('count'))),
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* R.bind('bindings', () => R.ask()),
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* R.map(({ count, bindings }) => count === RR.size(bindings))
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* )
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*
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* // The selector function to use with 'asks'.
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* // Returns value of the variable with specified name.
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* const lookupVar = (name: string) => (bindings: Bindings): number =>
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* pipe(
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* bindings,
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* RR.lookup(name),
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* O.getOrElse(() => 0)
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* )
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*
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* const sampleBindings: Bindings = { count: 3, a: 1, b: 2 }
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*
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* assert.deepStrictEqual(isCountCorrect(sampleBindings), true)
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*
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* @since 2.0.0
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*/
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import { Applicative2 } from './Applicative'
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import { Apply2 } from './Apply'
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import { Category2 } from './Category'
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import { Chain2 } from './Chain'
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import { Choice2 } from './Choice'
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import { Functor2 } from './Functor'
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import { Monad2 } from './Monad'
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import { Monoid } from './Monoid'
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import { Pointed2 } from './Pointed'
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import { Profunctor2 } from './Profunctor'
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import { ReadonlyNonEmptyArray } from './ReadonlyNonEmptyArray'
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import { Semigroup } from './Semigroup'
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import { Strong2 } from './Strong'
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/**
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* @category model
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* @since 2.0.0
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*/
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export interface Reader<R, A> {
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(r: R): A
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}
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/**
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* Reads the current context
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*
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* @category constructors
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* @since 2.0.0
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*/
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export declare const ask: <R>() => Reader<R, R>
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/**
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* Projects a value from the global context in a Reader
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*
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* @category constructors
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* @since 2.0.0
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*/
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export declare const asks: <R, A>(f: (r: R) => A) => Reader<R, A>
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/**
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* Changes the value of the local context during the execution of the action `ma` (similar to `Contravariant`'s
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* `contramap`).
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*
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* @example
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* import { pipe } from 'fp-ts/function'
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* import * as R from 'fp-ts/Reader'
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* import * as string from 'fp-ts/string'
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*
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* const calculateContentLen: R.Reader<string, number> = pipe(
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* R.Do,
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* R.bind('content', () => R.ask<string>()),
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* R.map(({ content }) => string.size(content))
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* )
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*
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* // Calls calculateContentLen after adding a prefix to the Reader content.
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* const calculateModifiedContentLen: R.Reader<string, number> = pipe(
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* calculateContentLen,
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* R.local((s) => 'Prefix ' + s)
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* )
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*
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* const s = '12345'
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*
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* assert.deepStrictEqual(
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* "Modified 's' length: " + calculateModifiedContentLen(s) + '\n' + "Original 's' length: " + calculateContentLen(s),
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* "Modified 's' length: 12\nOriginal 's' length: 5"
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* )
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*
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* @since 2.0.0
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*/
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export declare const local: <R2, R1>(f: (r2: R2) => R1) => <A>(ma: Reader<R1, A>) => Reader<R2, A>
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/**
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* Less strict version of [`asksReader`](#asksreader).
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*
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* The `W` suffix (short for **W**idening) means that the environment types will be merged.
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*
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* @category constructors
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* @since 2.11.0
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*/
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export declare const asksReaderW: <R1, R2, A>(f: (r1: R1) => Reader<R2, A>) => Reader<R1 & R2, A>
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/**
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* Effectfully accesses the environment.
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*
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* @category constructors
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* @since 2.11.0
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*/
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export declare const asksReader: <R, A>(f: (r: R) => Reader<R, A>) => Reader<R, A>
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/**
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* `map` can be used to turn functions `(a: A) => B` into functions `(fa: F<A>) => F<B>` whose argument and return types
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* use the type constructor `F` to represent some computational context.
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*
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* @category mapping
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* @since 2.0.0
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*/
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export declare const map: <A, B>(f: (a: A) => B) => <R>(fa: Reader<R, A>) => Reader<R, B>
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/**
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* Less strict version of [`ap`](#ap).
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*
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* The `W` suffix (short for **W**idening) means that the environment types will be merged.
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*
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* @since 2.8.0
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*/
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export declare const apW: <R2, A>(fa: Reader<R2, A>) => <R1, B>(fab: Reader<R1, (a: A) => B>) => Reader<R1 & R2, B>
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/**
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* @since 2.0.0
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*/
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export declare const ap: <R, A>(fa: Reader<R, A>) => <B>(fab: Reader<R, (a: A) => B>) => Reader<R, B>
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/**
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* @category constructors
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* @since 2.0.0
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*/
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export declare const of: <R = unknown, A = never>(a: A) => Reader<R, A>
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/**
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* Less strict version of [`chain`](#chain).
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*
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* The `W` suffix (short for **W**idening) means that the environment types will be merged.
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*
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* @category sequencing
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* @since 2.6.0
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*/
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export declare const chainW: <R2, A, B>(f: (a: A) => Reader<R2, B>) => <R1>(ma: Reader<R1, A>) => Reader<R1 & R2, B>
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/**
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* Composes computations in sequence, using the return value of one computation to determine the next computation.
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*
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* @category sequencing
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* @since 2.0.0
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*/
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export declare const chain: <A, R, B>(f: (a: A) => Reader<R, B>) => (ma: Reader<R, A>) => Reader<R, B>
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/**
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* Less strict version of [`flatten`](#flatten).
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*
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* The `W` suffix (short for **W**idening) means that the environment types will be merged.
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*
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* @category sequencing
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* @since 2.11.0
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*/
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export declare const flattenW: <R1, R2, A>(mma: Reader<R1, Reader<R2, A>>) => Reader<R1 & R2, A>
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/**
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* @category sequencing
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* @since 2.0.0
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*/
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export declare const flatten: <R, A>(mma: Reader<R, Reader<R, A>>) => Reader<R, A>
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/**
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* @since 2.0.0
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*/
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export declare const compose: <A, B>(ab: Reader<A, B>) => <C>(bc: Reader<B, C>) => Reader<A, C>
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/**
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* @since 2.0.0
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*/
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export declare const promap: <E, A, D, B>(f: (d: D) => E, g: (a: A) => B) => (fea: Reader<E, A>) => Reader<D, B>
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/**
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* @category constructors
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* @since 2.0.0
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*/
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export declare const id: Category2<URI>['id']
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/**
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* @since 2.10.0
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*/
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export declare const first: Strong2<URI>['first']
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/**
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* @since 2.10.0
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*/
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export declare const second: Strong2<URI>['second']
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/**
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* @since 2.10.0
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*/
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export declare const left: Choice2<URI>['left']
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/**
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* @since 2.10.0
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*/
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export declare const right: Choice2<URI>['right']
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/**
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* @category type lambdas
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* @since 2.0.0
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*/
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export declare const URI = 'Reader'
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/**
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* @category type lambdas
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* @since 2.0.0
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*/
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export declare type URI = typeof URI
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declare module './HKT' {
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interface URItoKind2<E, A> {
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readonly [URI]: Reader<E, A>
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}
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}
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/**
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* @category instances
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* @since 2.7.0
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*/
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export declare const Functor: Functor2<URI>
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/**
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* @category mapping
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* @since 2.10.0
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*/
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export declare const flap: <A>(a: A) => <E, B>(fab: Reader<E, (a: A) => B>) => Reader<E, B>
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/**
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* @category instances
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* @since 2.10.0
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*/
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export declare const Pointed: Pointed2<URI>
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/**
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* @category instances
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* @since 2.10.0
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*/
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export declare const Apply: Apply2<URI>
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/**
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* Combine two effectful actions, keeping only the result of the first.
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*
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* @since 2.0.0
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*/
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export declare const apFirst: <E, B>(second: Reader<E, B>) => <A>(first: Reader<E, A>) => Reader<E, A>
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/**
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* Less strict version of [`apFirst`](#apfirst).
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*
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* The `W` suffix (short for **W**idening) means that the environment types will be merged.
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*
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* @since 2.12.0
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*/
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export declare const apFirstW: <R2, B>(second: Reader<R2, B>) => <R1, A>(first: Reader<R1, A>) => Reader<R1 & R2, A>
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/**
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* Combine two effectful actions, keeping only the result of the second.
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*
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* @since 2.0.0
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*/
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export declare const apSecond: <E, B>(second: Reader<E, B>) => <A>(first: Reader<E, A>) => Reader<E, B>
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/**
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* Less strict version of [`apSecond`](#apsecond).
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*
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* The `W` suffix (short for **W**idening) means that the environment types will be merged.
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*
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* @since 2.12.0
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*/
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export declare const apSecondW: <R2, B>(second: Reader<R2, B>) => <R1, A>(first: Reader<R1, A>) => Reader<R1 & R2, B>
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/**
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* @category instances
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* @since 2.7.0
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*/
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export declare const Applicative: Applicative2<URI>
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/**
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* @category instances
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* @since 2.10.0
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*/
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export declare const Chain: Chain2<URI>
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/**
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* @category instances
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* @since 2.7.0
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*/
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export declare const Monad: Monad2<URI>
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/**
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* Composes computations in sequence, using the return value of one computation to determine the next computation and
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* keeping only the result of the first.
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*
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* @category sequencing
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* @since 2.0.0
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*/
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export declare const chainFirst: <A, R, B>(f: (a: A) => Reader<R, B>) => (first: Reader<R, A>) => Reader<R, A>
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/**
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* Less strict version of [`chainFirst`](#chainfirst).
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*
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* The `W` suffix (short for **W**idening) means that the environment types will be merged.
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*
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* @category sequencing
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* @since 2.11.0
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*/
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export declare const chainFirstW: <R2, A, B>(
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f: (a: A) => Reader<R2, B>
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) => <R1>(ma: Reader<R1, A>) => Reader<R1 & R2, A>
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/**
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* @category instances
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* @since 2.7.0
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*/
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export declare const Profunctor: Profunctor2<URI>
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/**
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* @category instances
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* @since 2.7.0
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*/
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export declare const Category: Category2<URI>
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/**
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* @category instances
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* @since 2.8.3
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*/
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export declare const Strong: Strong2<URI>
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/**
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* @category instances
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* @since 2.8.3
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*/
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export declare const Choice: Choice2<URI>
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/**
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* @category do notation
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* @since 2.8.0
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*/
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export declare const bindTo: <N extends string>(
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name: N
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) => <E, A>(fa: Reader<E, A>) => Reader<E, { readonly [K in N]: A }>
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declare const let_: <N extends string, A, B>(
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name: Exclude<N, keyof A>,
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f: (a: A) => B
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) => <E>(fa: Reader<E, A>) => Reader<E, { readonly [K in N | keyof A]: K extends keyof A ? A[K] : B }>
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export {
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/**
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* @category do notation
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* @since 2.13.0
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*/
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let_ as let
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}
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/**
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* @category do notation
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* @since 2.8.0
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*/
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export declare const bind: <N extends string, A, E, B>(
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name: Exclude<N, keyof A>,
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f: (a: A) => Reader<E, B>
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) => (ma: Reader<E, A>) => Reader<E, { readonly [K in N | keyof A]: K extends keyof A ? A[K] : B }>
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/**
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* The `W` suffix (short for **W**idening) means that the environment types will be merged.
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*
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* @category do notation
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* @since 2.8.0
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*/
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export declare const bindW: <N extends string, A, R2, B>(
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name: Exclude<N, keyof A>,
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f: (a: A) => Reader<R2, B>
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) => <R1>(fa: Reader<R1, A>) => Reader<
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R1 & R2,
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{
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readonly [K in keyof A | N]: K extends keyof A ? A[K] : B
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}
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>
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/**
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* @category do notation
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* @since 2.9.0
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*/
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export declare const Do: Reader<unknown, {}>
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/**
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* @category do notation
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* @since 2.8.0
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*/
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export declare const apS: <N extends string, A, E, B>(
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name: Exclude<N, keyof A>,
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fb: Reader<E, B>
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) => (fa: Reader<E, A>) => Reader<E, { readonly [K in N | keyof A]: K extends keyof A ? A[K] : B }>
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/**
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* Less strict version of [`apS`](#aps).
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*
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* The `W` suffix (short for **W**idening) means that the environment types will be merged.
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*
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* @category do notation
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* @since 2.8.0
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*/
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export declare const apSW: <A, N extends string, R2, B>(
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name: Exclude<N, keyof A>,
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fb: Reader<R2, B>
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) => <R1>(fa: Reader<R1, A>) => Reader<
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R1 & R2,
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{
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readonly [K in keyof A | N]: K extends keyof A ? A[K] : B
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}
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>
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/**
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* @since 2.11.0
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*/
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export declare const ApT: Reader<unknown, readonly []>
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/**
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* Equivalent to `ReadonlyNonEmptyArray#traverseWithIndex(Applicative)`.
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*
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* @category traversing
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* @since 2.11.0
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*/
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export declare const traverseReadonlyNonEmptyArrayWithIndex: <A, R, B>(
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f: (index: number, a: A) => Reader<R, B>
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) => (as: ReadonlyNonEmptyArray<A>) => Reader<R, ReadonlyNonEmptyArray<B>>
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/**
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* Equivalent to `ReadonlyArray#traverseWithIndex(Applicative)`.
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*
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* @category traversing
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* @since 2.11.0
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*/
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export declare const traverseReadonlyArrayWithIndex: <A, R, B>(
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f: (index: number, a: A) => Reader<R, B>
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) => (as: readonly A[]) => Reader<R, readonly B[]>
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/**
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* Equivalent to `ReadonlyArray#traverseWithIndex(Applicative)`.
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*
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* @category traversing
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* @since 2.9.0
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*/
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export declare const traverseArrayWithIndex: <R, A, B>(
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f: (index: number, a: A) => Reader<R, B>
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) => (as: ReadonlyArray<A>) => Reader<R, ReadonlyArray<B>>
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/**
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* Equivalent to `ReadonlyArray#traverse(Applicative)`.
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*
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* @category traversing
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* @since 2.9.0
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*/
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export declare const traverseArray: <R, A, B>(
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f: (a: A) => Reader<R, B>
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) => (as: readonly A[]) => Reader<R, readonly B[]>
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/**
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* Equivalent to `ReadonlyArray#sequence(Applicative)`.
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*
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* @category traversing
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* @since 2.9.0
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*/
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export declare const sequenceArray: <R, A>(arr: ReadonlyArray<Reader<R, A>>) => Reader<R, ReadonlyArray<A>>
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/**
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* This instance is deprecated, use small, specific instances instead.
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* For example if a function needs a `Functor` instance, pass `R.Functor` instead of `R.reader`
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* (where `R` is from `import R from 'fp-ts/Reader'`)
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*
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* @category zone of death
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* @since 2.0.0
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* @deprecated
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*/
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export declare const reader: Monad2<URI> & Profunctor2<URI> & Category2<URI> & Strong2<URI> & Choice2<URI>
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/**
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* Use [`getApplySemigroup`](./Apply.ts.html#getapplysemigroup) instead.
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*
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* @category zone of death
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* @since 2.0.0
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* @deprecated
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*/
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export declare const getSemigroup: <R, A>(S: Semigroup<A>) => Semigroup<Reader<R, A>>
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/**
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* Use [`getApplicativeMonoid`](./Applicative.ts.html#getapplicativemonoid) instead.
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*
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* @category zone of death
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* @since 2.0.0
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* @deprecated
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*/
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export declare const getMonoid: <R, A>(M: Monoid<A>) => Monoid<Reader<R, A>>
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