Monads

<p align="center"> <a href="https://thames-technology.github.io/monads"> <img src="https://raw.githubusercontent.com/thames-technology/monads/main/.github/assets/monads-cover.png" alt="Monads Logo" /> </a> </p> <p align="right"> <i>If you use this repo, star it ✨</i> </p>

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<h2 align="center">Option, Result, and Either types for JavaScript</h2> <p align="center"> 🦀 Inspired by <a href="https://doc.rust-lang.org/stable/std/option/" target="_blank">Rust</a> </p> <p align="center"> <b>Zero dependencies</b> • <b>Lightweight</b> • <b>Functional</b> </p>

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Install

npm install @thames/monads

Getting started

The Option<T> type

Option represents an optional value: every Option is either Some and contains a value, or None, and does not.

[!NOTE] Full documentation here: Option

import { Option, Some, None } from '@thames/monads';

const divide = (numerator: number, denominator: number): Option<number> => {
  if (denominator === 0) {
    return None;
  } else {
    return Some(numerator / denominator);
  }
};

// The return value of the function is an option
const result = divide(2.0, 3.0);

// Pattern match to retrieve the value
const message = result.match({
  some: (res) => `Result: ${res}`,
  none: 'Cannot divide by 0',
});

console.log(message); // "Result: 0.6666666666666666"

The Result<T, E> type

Result represents a value that is either a success (Ok) or a failure (Err).

[!NOTE] Full documentation here: Result

import { Result, Ok, Err } from '@thames/monads';

const getIndex = (values: string[], value: string): Result<number, string> => {
  const index = values.indexOf(value);

  switch (index) {
    case -1:
      return Err('Value not found');
    default:
      return Ok(index);
  }
};

const values = ['a', 'b', 'c'];

getIndex(values, 'b'); // Ok(1)
getIndex(values, 'z'); // Err("Value not found")

The Either<L, R> type

Either represents a value that is either Left or Right. It is a powerful way to handle operations that can result in two distinctly different types of outcomes.

[!NOTE] Full documentation here: Either

import { Either, Left, Right } from '@thames/monads';

const divide = (numerator: number, denominator: number): Either<string, number> => {
  if (denominator === 0) {
    return Left('Cannot divide by 0');
  } else {
    return Right(numerator / denominator);
  }
};

const result = divide(2.0, 3.0);

const message = result.match({
  left: (err) => `Error: ${err}`,
  right: (res) => `Result: ${res}`,
});

console.log(message); // "Result: 0.6666666666666666"