npm install --save @hexadrop/either

Using bun

bun add @hexadrop/either

What it does

It provides an implementation of the Either monad in TypeScript. The Either monad is a popular functional programming concept used to handle computations that can result in two possible outcomes: a successful result (Right) or an error (Left). This is useful for handling computations that can fail, providing a way to chain operations while keeping error handling separate.

How to use

The @hexadrop/either package default exports a class Either with methods to create an instance representing a left or right value (Either.left and Either.right), check the type of the value (isLeft and isRight), retrieve the value (getLeft, getRight, getLeftOrElse, getRightOrElse), and transform the value (mapLeft, mapRight, flatMapLeft, flatMapRight).

Creating an instance

import Either from '@hexadrop/either';

// Create a Right value
const right = Either.right('This is a right value');
console.log(right.isRight()); // true
console.log(right.getRight()); // 'This is a right value'

// Create a Left value
const left = Either.left('This is a left value');
console.log(left.isLeft()); // true
console.log(left.getLeft()); // 'This is a left value'

Transforming the value

// Use mapRight to transform a Right value
const transformedRight = right.mapRight(value => value.toUpperCase());
console.log(transformedRight.getRight()); // 'THIS IS A RIGHT VALUE'

// Use mapLeft to transform a Left value
const transformedLeft = left.mapLeft(value => value.toUpperCase());
console.log(transformedLeft.getLeft()); // 'THIS IS A LEFT VALUE'

Using flatMap

// Use flatMapRight to transform a Right value into a new Either
const flatMappedRight = right.flatMapRight(value => Either.right(value.length));
console.log(flatMappedRight.getRight()); // 20

// Use flatMapLeft to transform a Left value into a new Either
const flatMappedLeft = left.flatMapLeft(value => Either.left(value.length));
console.log(flatMappedLeft.getLeft()); // 19

Hexadrop Code Quality Standards

Publishing this package we are committing ourselves to the following code quality standards:

• Respect Semantic Versioning: No breaking changes in patch or minor versions
• No surprises in transitive dependencies: Use the bare minimum dependencies needed to meet the purpose
• One specific purpose to meet without having to carry a bunch of unnecessary other utilities
• Tests as documentation and usage examples
• Well documented README showing how to install and use
• License favoring Open Source and collaboration