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index.js
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index.js
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/// <reference path="index.d.ts"/>
/** @typedef {import('either-ts')} Sig */
/** @type {Sig['left']} */
exports.left = value => new Left(value)
/** @type {Sig['right']} */
exports.right = value => new Right(value)
/** @type {Sig['create']} */
exports.create = function(isRight, leftThunk, rightThunk) {
return isRight ? exports.right(rightThunk()) : exports.left(leftThunk())
}
/** @type {Sig['fromThrowable']} */
exports.fromThrowable = thunk => {
try {
return exports.right(thunk())
} catch(e) {
return exports.left(e)
}
}
/** @type {Sig['fromNullable']} */
exports.fromNullable = err => nullable =>
nullable == null ? exports.left(err) : exports.right(nullable)
/**
@template L, R
@type {Sig['partition']}
*/
exports.partition = es => {
/** @type {L[]} */
const ls = []
/** @type {R[]} */
const rs = []
for(const e of es) e
.leftMap(left => ls.push(left))
.map(right => rs.push(right))
return [ls, rs]
}
/**
@template L, R
@type {Sig['sequence']}
*/
exports.sequence = es => {
/** @type {R[]} */
const rs = []
for(const e of es) {
if (!e.isOk) return e
rs.push(e.value)
}
return exports.right(rs)
}
/** @template L, R */
class Left {
/** @param {L} value */
constructor(value) { this.leftValue = value }
get value() { return this.leftValue }
get isOk() { return false }
/**
@template L2
@param {function(L): L2} f
*/
leftMap(f) {
return new Left(f(this.leftValue))
}
/**
@template R2
@param {function(R): R2} _
*/
map(_) {
return new Left(this.leftValue)
}
/**
@template L2
@param {function(L): Promise<L2>} f
*/
async leftMapThen(f) {
return new Left(await f(this.leftValue))
}
/**
@template R2
@param {function(R): R2} _
*/
async mapThen(_) {
return Promise.resolve(new Left(this.leftValue))
}
/**
@template L2
@param {function(L): Either<L2, R>} f
*/
leftFlatMap(f) {
return f(this.leftValue)
}
/**
@template R2
@param {function(R): Either<L, R2>} _
*/
flatMap(_) {
return new Left(this.leftValue)
}
/**
@template L2
@param {function(L): Promise<Either<L2, R>>} f
*/
async leftFlatMapThen(f) {
return await f(this.leftValue)
}
/**
@template R2
@param {function(R): Promise<Either<L, R2>>} f
*/
flatMapThen(f) {
return Promise.resolve(new Left(this.leftValue))
}
/** @param {function(L): R} f */
rightOrElse(f) {
return f(this.leftValue)
}
}
/** @template L, R */
class Right {
/** @param {R} value */
constructor(value) { this.rightValue = value }
get value() { return this.rightValue }
get isOk() { return true }
/**
@template L2
@param {function(L): L2} _
*/
leftMap(_) {
return new Right(this.rightValue)
}
/**
@template R2
@param {function(R): R2} f
*/
map(f) {
return new Right(f(this.rightValue))
}
/**
@template L2
@param {function(L): Promise<L2>} _
*/
async leftMapThen(_) {
return Promise.resolve(new Right(this.rightValue))
}
/**
@template R2
@param {function(R): Promise<R2>} f
*/
async mapThen(f) {
return new Right(await f(this.rightValue))
}
/**
@template L2
@param {function(L): Either<L2, R>} _
*/
leftFlatMap(_) {
return new Right(this.rightValue)
}
/**
@template R2
@param {function(R): Either<L, R2>} f
*/
flatMap(f) {
return f(this.rightValue)
}
/**
@template L2
@param {function(L): Promise<Either<L2, R>>} f
*/
leftFlatMapThen(f) {
return Promise.resolve(new Right(this.rightValue))
}
/**
@template R2
@param {function(R): Promise<Either<L, R2>>} f
*/
async flatMapThen(f) {
return await f(this.rightValue)
}
/** @param {function(L): R} _ */
rightOrElse(_) {
return this.rightValue
}
}