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/*
*******************************************************************************
* Copyright © 2024-present Jonathan Barronville <jonathanmarvens@proton.me> *
* *
* Licensed under the Apache License, Version 2.0 (the "License"); you may not *
* use this file except in compliance with the License. *
* You may obtain a copy of the License at *
* *
* http://www.apache.org/licenses/LICENSE-2.0 *
* *
* Unless required by applicable law or agreed to in writing, software *
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT *
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. *
* See the License for the specific language governing permissions and *
* limitations under the License. *
*******************************************************************************
*/
import assert from './utilities/assert'
import { customSymbol as customNodeJsUtilInspectSymbol } from './utilities/node-js-util-inspect'
import ExpectationError from './error/expectation'
import { failure } from './result'
import ImproperUnwrapError from './error/improper-unwrap'
import nodeJsUtilInspect from './utilities/node-js-util-inspect'
import type Result from './result'
import { success } from './result'
import UnreachableCodeError from './error/unreachable-code'
/**
* A robust abstraction for handling optional values.
*/
abstract class Maybe<TValue> {
protected constructor() { }
#convertToString(toStringFunction: (value: unknown) => string) {
if (this.isSomething()) {
const value = this.unwrap()
const valueString = toStringFunction(value)
.split('\n')
.map((line) => ` ${line}`)
.join('\n')
.trimStart()
return `
Maybe{
Something{
value: ${valueString},
}
}
`.trim()
} else if (this.isNothing()) {
return `
Maybe{
Nothing{}
}
`.trim()
} else {
throw new UnreachableCodeError('Reached an unreachable code path')
}
}
protected abstract _and<TOtherValue>(other: Maybe<TOtherValue>): Maybe<TOtherValue>
protected abstract _andThen<TOtherValue>(f: (value: TValue) => Maybe<TOtherValue>): Maybe<TOtherValue>
protected abstract _expect(message: string): TValue
protected abstract _filter(predicate: (value: TValue) => boolean): Maybe<TValue>
protected abstract _getSuccessOr<TError extends NonNullable<unknown>>(error: TError): Result<TValue, TError>
protected abstract _inspect(f: (value: TValue) => void): Maybe<TValue>
protected abstract _isNothing(): boolean
protected abstract _isNothingOr(predicate: (value: TValue) => boolean): boolean
protected abstract _isSomething(): boolean
protected abstract _isSomethingAnd(predicate: (value: TValue) => boolean): boolean
protected abstract _map<TNewValue>(f: (value: TValue) => TNewValue): Maybe<TNewValue>
protected abstract _or(other: Maybe<TValue>): Maybe<TValue>
protected abstract _unwrap(): TValue
/**
* If this is a `Something` {@link Maybe}, returns {@link other}.
* If this is a `Nothing` {@link Maybe}, returns this {@link Maybe}.
*
* @param other The {@link Maybe} to return if this is a `Something` {@link Maybe}.
*/
public and<TOtherValue>(other: Maybe<TOtherValue>) {
assert(isMaybe(other))
return this._and(other)
}
/**
* If this is a `Something` {@link Maybe}, returns the result of applying {@link f} to the contained value.
* If this is a `Nothing` {@link Maybe}, returns this {@link Maybe}.
*
* @param f The function to apply to the contained value.
*/
public andThen<TOtherValue>(f: (value: TValue) => Maybe<TOtherValue>) {
assert(typeof f === 'function')
return this._andThen(f)
}
/**
* If this is a `Something` {@link Maybe}, returns the contained value.
* If this is a `Nothing` {@link Maybe}, throws an {@link ExpectationError} with the provided {@link message}.
*
* @param message The message to include in the {@link ExpectationError}.
*/
public expect(message: string) {
assert(typeof message === 'string')
return this._expect(message)
}
/**
* If this is a `Something` {@link Maybe}, returns this {@link Maybe} if the contained value satisfies the provided {@link predicate}.
* If this is a `Nothing` {@link Maybe}, returns this {@link Maybe}.
*
* @param predicate The predicate to apply to the contained value.
*/
public filter(predicate: (value: TValue) => boolean) {
assert(typeof predicate === 'function')
return this._filter(predicate)
}
/**
* If this is a `Something` {@link Maybe}, returns a `Success` {@link Result} containing the contained value.
* If this is a `Nothing` {@link Maybe}, returns a `Failure` {@link Result} containing the provided {@link error}.
*
* @param error The error to include in the `Failure` {@link Result}.
*/
public getSuccessOr<TError extends NonNullable<unknown>>(error: TError) {
return this._getSuccessOr(error)
}
/**
* If this is a `Something` {@link Maybe}, applies {@link f} to the contained value and returns this {@link Maybe}.
* If this is a `Nothing` {@link Maybe}, returns this {@link Maybe}.
*
* @param f The function to apply to the contained value.
*/
public inspect(f: (value: TValue) => void) {
assert(typeof f === 'function')
return this._inspect(f)
}
/**
* If this is a `Something` {@link Maybe}, returns `false`.
* If this is a `Nothing` {@link Maybe}, returns `true`.
*/
public isNothing() {
return this._isNothing()
}
/**
* If this is a `Something` {@link Maybe}, returns the result of applying {@link predicate} to the contained value.
* If this is a `Nothing` {@link Maybe}, returns `true`.
*
* @param predicate The predicate to apply to the contained value.
*/
public isNothingOr(predicate: (value: TValue) => boolean) {
assert(typeof predicate === 'function')
return this._isNothingOr(predicate)
}
/**
* If this is a `Something` {@link Maybe}, returns `true`.
* If this is a `Nothing` {@link Maybe}, returns `false`.
*/
public isSomething() {
return this._isSomething()
}
/**
* If this is a `Something` {@link Maybe}, returns the result of applying {@link predicate} to the contained value.
* If this is a `Nothing` {@link Maybe}, returns `false`.
*
* @param predicate The predicate to apply to the contained value.
*/
public isSomethingAnd(predicate: (value: TValue) => boolean) {
assert(typeof predicate === 'function')
return this._isSomethingAnd(predicate)
}
/**
* If this is a `Something` {@link Maybe}, returns a `Something` {@link Maybe} containing the result of applying {@link f} to the contained value.
* If this is a `Nothing` {@link Maybe}, returns this {@link Maybe}.
*
* @param f The function to apply to the contained value.
*/
public map<TNewValue>(f: (value: TValue) => TNewValue) {
assert(typeof f === 'function')
return this._map(f)
}
/**
* If this is a `Something` {@link Maybe}, returns this {@link Maybe}.
* If this is a `Nothing` {@link Maybe}, returns {@link other}.
*
* @param other The {@link Maybe} to return if this is a `Nothing` {@link Maybe}.
*/
public or(other: Maybe<TValue>) {
assert(isMaybe(other))
return this._or(other)
}
public toString() {
return this.#convertToString((value) => `${value}`)
}
/**
* If this is a `Something` {@link Maybe}, returns the contained value.
* If this is a `Nothing` {@link Maybe}, throws an {@link ImproperUnwrapError}.
*/
public unwrap() {
return this._unwrap()
}
public [customNodeJsUtilInspectSymbol]() {
return this.#convertToString((value) => {
return nodeJsUtilInspect(value)
})
}
}
class Nothing extends Maybe<never> {
static #instance: Nothing
static {
const instance = new this()
this.#instance = instance
}
public static make() {
return this.#instance
}
private constructor() {
super()
}
protected _and() {
return this
}
protected _andThen() {
return this
}
protected _expect(message: string): never {
throw new ExpectationError(message)
}
protected _filter() {
return this
}
protected _getSuccessOr<TError extends NonNullable<unknown>>(error: TError) {
return failure<never, TError>(error)
}
protected _inspect() {
return this
}
protected _isNothing() {
return true
}
protected _isNothingOr() {
return true
}
protected _isSomething() {
return false
}
protected _isSomethingAnd() {
return false
}
protected _map() {
return this
}
protected _or(other: Maybe<never>) {
return other
}
protected _unwrap(): never {
throw new ImproperUnwrapError('Attempted to unwrap a `Nothing` value')
}
}
class Something<TValue> extends Maybe<TValue> {
public static make<TValue>(value: TValue) {
return new this(value)
}
#value: TValue
private constructor(value: TValue) {
super()
this.#value = value
}
protected _and<TOtherValue>(other: Maybe<TOtherValue>) {
return other
}
protected _andThen<TOtherValue>(f: (value: TValue) => Maybe<TOtherValue>) {
const value = f(this.#value)
assert(isMaybe(value))
return value
}
protected _expect() {
return this.#value
}
protected _filter(predicate: (value: TValue) => boolean) {
const isSatified = predicate(this.#value)
assert(typeof isSatified === 'boolean')
return isSatified ?
this :
Nothing.make()
}
protected _getSuccessOr() {
return success<TValue, never>(this.#value)
}
protected _inspect(f: (value: TValue) => void) {
f(this.#value)
return this
}
protected _isNothing() {
return false
}
protected _isNothingOr(predicate: (value: TValue) => boolean) {
const isSatified = predicate(this.#value)
assert(typeof isSatified === 'boolean')
return isSatified
}
protected _isSomething() {
return true
}
protected _isSomethingAnd(predicate: (value: TValue) => boolean) {
const isSatified = predicate(this.#value)
assert(typeof isSatified === 'boolean')
return isSatified
}
protected _map<TNewValue>(f: (value: TValue) => TNewValue) {
const value = f(this.#value)
return Something.make(value)
}
protected _or() {
return this
}
protected _unwrap() {
return this.#value
}
}
/**
* Checks if the provided {@link value} is a {@link Maybe}.
*
* @param value The value to check.
*/
function isMaybe(value: unknown): value is Maybe<unknown> {
return (value instanceof Maybe)
}
/**
* Creates and returns a new `Nothing` {@link Maybe}.
*/
function nothing<TValue = any>(): Maybe<TValue> {
return Nothing.make()
}
/**
* Creates and returns a new `Something` {@link Maybe} containing the provided {@link value}.
*
* @param value The value to contain in the new `Something` {@link Maybe}.
*/
function something<TValue = any>(value: TValue): Maybe<TValue> {
return Something.make(value)
}
export {
type Maybe as default,
isMaybe,
nothing,
something,
}