imskojs / monads

👻 Type safe Option and Result type – for TypeScript and JavaScript

Monads

Type safe Option and Result types – inspired by Rust.

Prereqs & Install

• Node >=9.10.0
• npm >=6.1.0

Please note that the TypeScript target is ES6.

npm install @usefultools/monads

Documentation

• Option Type
• Result Type

Usage

Option<T>

See full Option<T> API documentation here.

import { Option, Some, None } from "@usefultools/monads"

function 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"

More Option<T> examples here.

Result<T, E>

See full Result<T, E> API documentation here.

import { Result, Ok, Err } from "@usefultools/monads"

function 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)
  }
}

console.log(getIndex(["a", "b", "c"], "b")) // Ok(1)
console.log(getIndex(["a", "b", "c"], "z")) // Err("Value not found")

More Result<T, E> examples here.

Contributing

If you have comments, complaints, or ideas for improvements, feel free to open an issue or a pull request! See Contributing guide for details about project setup, testing, etc.

Author and license

This library was created by @LITCHI.IO. Main author and maintainer is Slavo Vojacek.

Contributors: Slavo Vojacek

@usefultools/monads is available under the ISC license. See the LICENSE file for more info.