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Writer.ts
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Writer.ts
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/**
* @since 2.0.0
*/
import { Applicative2C } from './Applicative'
import { Apply2C } from './Apply'
import { Chain2C } from './Chain'
import { pipe } from './function'
import { flap as flap_, Functor2 } from './Functor'
import { Monad2C } from './Monad'
import { Monoid } from './Monoid'
import { Pointed2C } from './Pointed'
import { Semigroup } from './Semigroup'
// -------------------------------------------------------------------------------------
// model
// -------------------------------------------------------------------------------------
/**
* @category model
* @since 2.0.0
*/
export interface Writer<W, A> {
(): [A, W]
}
// -------------------------------------------------------------------------------------
// constructors
// -------------------------------------------------------------------------------------
/**
* Appends a value to the accumulator
*
* @category constructors
* @since 2.0.0
*/
export const tell: <W>(w: W) => Writer<W, void> = (w) => () => [undefined, w]
// -------------------------------------------------------------------------------------
// combinators
// -------------------------------------------------------------------------------------
/**
* Modifies the result to include the changes to the accumulator
*
* @since 2.0.0
*/
export const listen: <W, A>(fa: Writer<W, A>) => Writer<W, [A, W]> = (fa) => () => {
const [a, w] = fa()
return [[a, w], w]
}
/**
* Applies the returned function to the accumulator
*
* @since 2.0.0
*/
export const pass: <W, A>(fa: Writer<W, [A, (w: W) => W]>) => Writer<W, A> = (fa) => () => {
const [[a, f], w] = fa()
return [a, f(w)]
}
/**
* Projects a value from modifications made to the accumulator during an action
*
* @since 2.0.0
*/
export const listens: <W, B>(f: (w: W) => B) => <A>(fa: Writer<W, A>) => Writer<W, [A, B]> = (f) => (fa) => () => {
const [a, w] = fa()
return [[a, f(w)], w]
}
/**
* Modify the final accumulator value by applying a function
*
* @since 2.0.0
*/
export const censor: <W>(f: (w: W) => W) => <A>(fa: Writer<W, A>) => Writer<W, A> = (f) => (fa) => () => {
const [a, w] = fa()
return [a, f(w)]
}
/* istanbul ignore next */
const _map: Functor2<URI>['map'] = (fa, f) => pipe(fa, map(f))
/**
* `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.
*
* @category mapping
* @since 2.0.0
*/
export const map: <A, B>(f: (a: A) => B) => <E>(fa: Writer<E, A>) => Writer<E, B> = (f) => (fa) => () => {
const [a, w] = fa()
return [f(a), w]
}
/**
* @category type lambdas
* @since 2.0.0
*/
export const URI = 'Writer'
/**
* @category type lambdas
* @since 2.0.0
*/
export type URI = typeof URI
declare module './HKT' {
interface URItoKind2<E, A> {
readonly [URI]: Writer<E, A>
}
}
/**
* @category instances
* @since 2.10.0
*/
export const getPointed = <W>(M: Monoid<W>): Pointed2C<URI, W> => ({
URI,
_E: undefined as any,
of: (a) => () => [a, M.empty]
})
/**
* @category instances
* @since 2.10.0
*/
export const getApply = <W>(S: Semigroup<W>): Apply2C<URI, W> => ({
URI,
_E: undefined as any,
map: _map,
ap: (fab, fa) => () => {
const [f, w1] = fab()
const [a, w2] = fa()
return [f(a), S.concat(w1, w2)]
}
})
/**
* @category instances
* @since 2.10.0
*/
export const getApplicative = <W>(M: Monoid<W>): Applicative2C<URI, W> => {
const A = getApply(M)
const P = getPointed(M)
return {
URI,
_E: undefined as any,
map: _map,
ap: A.ap,
of: P.of
}
}
/**
* @category instances
* @since 2.10.0
*/
export function getChain<W>(S: Semigroup<W>): Chain2C<URI, W> {
const A = getApply(S)
return {
URI,
_E: undefined as any,
map: _map,
ap: A.ap,
chain: (fa, f) => () => {
const [a, w1] = fa()
const [b, w2] = f(a)()
return [b, S.concat(w1, w2)]
}
}
}
/**
* @category instances
* @since 2.0.0
*/
export function getMonad<W>(M: Monoid<W>): Monad2C<URI, W> {
const A = getApplicative(M)
const C = getChain(M)
return {
URI,
_E: undefined as any,
map: _map,
ap: A.ap,
of: A.of,
chain: C.chain
}
}
/**
* @category instances
* @since 2.7.0
*/
export const Functor: Functor2<URI> = {
URI,
map: _map
}
/**
* @category mapping
* @since 2.10.0
*/
export const flap = /*#__PURE__*/ flap_(Functor)
// -------------------------------------------------------------------------------------
// utils
// -------------------------------------------------------------------------------------
/**
* @since 2.8.0
*/
export const evaluate: <W, A>(fa: Writer<W, A>) => A = (fa) => fa()[0]
/**
* @since 2.8.0
*/
export const execute: <W, A>(fa: Writer<W, A>) => W = (fa) => fa()[1]
// -------------------------------------------------------------------------------------
// deprecated
// -------------------------------------------------------------------------------------
/**
* Use [`evaluate`](#evaluate) instead
*
* @category zone of death
* @since 2.0.0
* @deprecated
*/
export const evalWriter: <W, A>(fa: Writer<W, A>) => A = (fa) => fa()[0]
/**
* Use [`execute`](#execute) instead
*
* @category zone of death
* @since 2.0.0
* @deprecated
*/
export const execWriter: <W, A>(fa: Writer<W, A>) => W = (fa) => fa()[1]
/**
* Use [`Functor`](#functor) instead.
*
* @category zone of death
* @since 2.0.0
* @deprecated
*/
export const writer: Functor2<URI> = Functor