eaux

A lightweight and functional-style library that provides robust abstractions for handling optional values and handling operations that can either succeed or fail. By making states explicit, it encourages precise and deliberate management of application logic.

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Overview

eaux introduces two core abstractions:

• Maybe

  Represents an optional value. A Maybe can either be a Nothing containing no value or a Something containing a value.

• Result

  Represents the outcome of an operation that can either succeed or fail. A Result can either be a Failure containing an error or a Success containing a value.

Both abstractions support a suite of chainable and composable operations that lead to code that is clear, consistent, and reliable.

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Installation

To install eaux, ensure that you have Node.js version 20 or newer, and use your preferred package manager.

npm

npm install eaux

pnpm

pnpm add eaux

yarn

yarn add eaux

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API

Below is a complete overview of the functions and methods exposed by the library.

Maybe

Functions

• something<TValue = any>(value: TValue): Maybe<TValue>

  Creates and returns a new Something Maybe containing the provided value.

• nothing<TValue = any>(): Maybe<TValue>

  Creates and returns a new Nothing Maybe.

• isMaybe(value: unknown): value is Maybe<unknown>

  Checks if the provided value is a Maybe.

Methods

On a Maybe instance, the following methods are available:

• and<TOtherValue>(other: Maybe<TOtherValue>): Maybe<TOtherValue>

  If this is a Something Maybe, returns other. If this is a Nothing Maybe, returns this Maybe.

• andThen<TOtherValue>(f: (value: TValue) => Maybe<TOtherValue>): Maybe<TOtherValue>

  If this is a Something Maybe, returns the result of applying f to the contained value. If this is a Nothing Maybe, returns this Maybe.

• expect(message: string): TValue

  If this is a Something Maybe, returns the contained value. If this is a Nothing Maybe, throws an ExpectationError with the provided message.

• filter(predicate: (value: TValue) => boolean): Maybe<TValue>

  If this is a Something Maybe, returns this Maybe if the contained value satisfies the provided predicate. If this is a Nothing Maybe, returns this Maybe.

• getSuccessOr<TError>(error: TError): Result<TValue, TError>

  If this is a Something Maybe, returns a Success Result containing the contained value. If this is a Nothing Maybe, returns a Failure Result containing the provided error.

• inspect(f: (value: TValue) => void): Maybe<TValue>

  If this is a Something Maybe, applies f to the contained value and returns this Maybe. If this is a Nothing Maybe, returns this Maybe.

• isNothing(): boolean

  If this is a Something Maybe, returns false. If this is a Nothing Maybe, returns true.

• isNothingOr(predicate: (value: TValue) => boolean): boolean

  If this is a Something Maybe, returns the result of applying predicate to the contained value. If this is a Nothing Maybe, returns true.

• isSomething(): boolean

  If this is a Something Maybe, returns true. If this is a Nothing Maybe, returns false.

• isSomethingAnd(predicate: (value: TValue) => boolean): boolean

  If this is a Something Maybe, returns the result of applying predicate to the contained value. If this is a Nothing Maybe, returns false.

• map<TNewValue>(f: (value: TValue) => TNewValue): Maybe<TNewValue>

  If this is a Something Maybe, returns a Something Maybe containing the result of applying f to the contained value. If this is a Nothing Maybe, returns this Maybe.

• or(other: Maybe<TValue>): Maybe<TValue>

  If this is a Something Maybe, returns this Maybe. If this is a Nothing Maybe, returns other.

• unwrap(): TValue

  If this is a Something Maybe, returns the contained value. If this is a Nothing Maybe, throws an ImproperUnwrapError.

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Result

Functions

• success<TValue = any, TError = any>(value: TValue): Result<TValue, TError>

  Creates and returns a new Success Result containing the provided value.

• failure<TValue = any, TError = any>(error: TError): Result<TValue, TError>

  Creates and returns a new Failure Result containing the provided error.

• isResult(value: unknown): value is Result<unknown, unknown>

  Checks if the provided value is a Result.

Methods

On a Result instance, the following methods are available:

• and<TOtherValue>(other: Result<TOtherValue, TError>): Result<TOtherValue, TError>

  If this is a Success Result, returns other. If this is a Failure Result, returns this Result.

• andThen<TOtherValue>(f: (value: TValue) => Result<TOtherValue, TError>): Result<TOtherValue, TError>

  If this is a Success Result, returns the result of applying f to the contained value. If this is a Failure Result, returns this Result.

• expect(message: string): TValue

  If this is a Success Result, returns the contained value. If this is a Failure Result, throws an ExpectationError with the provided message.

• expectFailure(message: string): TError

  If this is a Success Result, throws an ExpectationError with the provided message. If this is a Failure Result, returns the contained error.

• getFailure(): Maybe<TError>

  If this is a Success Result, returns a Nothing Maybe. If this is a Failure Result, returns a Something Maybe containing the contained error.

• getSuccess(): Maybe<TValue>

  If this is a Success Result, returns a Something Maybe containing the contained value. If this is a Failure Result, returns a Nothing Maybe.

• inspect(f: (value: TValue) => void): Result<TValue, TError>

  If this is a Success Result, applies f to the contained value and returns this Result. If this is a Failure Result, returns this Result.

• inspectFailure(f: (error: TError) => void): Result<TValue, TError>

  If this is a Success Result, returns this Result. If this is a Failure Result, applies f to the contained error and returns this Result.

• isFailure(): boolean

  If this is a Success Result, returns false. If this is a Failure Result, returns true.

• isFailureAnd(predicate: (error: TError) => boolean): boolean

  If this is a Success Result, returns false. If this is a Failure Result, returns the result of applying predicate to the contained error.

• isSuccess(): boolean

  If this is a Success Result, returns true. If this is a Failure Result, returns false.

• isSuccessAnd(predicate: (value: TValue) => boolean): boolean

  If this is a Success Result, returns the result of applying predicate to the contained value. If this is a Failure Result, returns false.

• map<TNewValue>(f: (value: TValue) => TNewValue): Result<TNewValue, TError>

  If this is a Success Result, returns a Success Result containing the result of applying f to the contained value. If this is a Failure Result, returns this Result.

• mapFailure<TNewError>(f: (error: TError) => TNewError): Result<TValue, TNewError>

  If this is a Success Result, returns this Result. If this is a Failure Result, returns a Failure Result containing the result of applying f to the contained error.

• or<TOtherError>(other: Result<TValue, TOtherError>): Result<TValue, TOtherError>

  If this is a Success Result, returns this Result. If this is a Failure Result, returns other.

• unwrap(): TValue

  If this is a Success Result, returns the contained value. If this is a Failure Result, throws an ImproperUnwrapError.

• unwrapFailure(): TError

  If this is a Success Result, throws an ImproperUnwrapError. If this is a Failure Result, returns the contained error.

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Usage

The following examples illustrate some real-world scenarios where eaux can be useful.

Example 1: Handling Optional User Input

Assume you want to process user input that might be empty. With Maybe, you can ensure that every code path explicitly checks whether the value exists.

import { nothing, something } from 'eaux'

// A function that simulates reading user input.
function getUserInput() {
  // Imagine a real implementation here.
  const randomNumber = Math.random()
  return (randomNumber > 0.5) ?
    'Hello, world!' :
    null
}

const input = getUserInput()
const maybeInput = (input !== null) ?
  something(input) :
  nothing()

if (maybeInput.isSomething()) {
  console.log('User input provided:', maybeInput.unwrap())
} else {
  console.log('No user input was provided')
}

Example 2: Parsing Numbers with Result

Imagine a routine that attempts to parse a string into a number. By using Result, you enforce error handling explicitly.

import { failure, success } from 'eaux'

function parseNumber(input: string): Result<number, string> {
  const parsedValue = Number(input)
  // Check for non-numeric values.
  if (isNaN(parsedValue)) {
    return failure('Invalid number format, expected a numeric string.')
  }
  return success(parsedValue)
}

const result = parseNumber('42') // Try changing `'42'` to an invalid input.

if (result.isSuccess()) {
  console.log('Number parsed:', result.unwrap())
} else {
  console.error('Error parsing number:', result.unwrapFailure())
}

Example 3: Transforming Values with Chainable Operations

Combine operations using chainable methods to build complex logic that is both clear and explicit.

import { nothing, something } from 'eaux'

function doubleValue(value: number): number {
  return (value * 2)
}

const maybeValue = something(21)

// Chain the operations: if the value exists, double it; otherwise, do nothing.
const transformedValue = maybeValue
  .map(doubleValue)
  .or(something(0))

console.log('Value transformed:', transformedValue.unwrap())

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License

This project is licensed under the Apache License, Version 2.0. See the accompanying LICENSE file for details.

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