🍋 lemonade

Node.js implementation of some monads found in Elm.

📦 Requirements

• Node.js

⬇️ Installation

$ npm install aminnairi/lemonade

✨ Examples

🤔 Maybe

const { Maybe: { Nothing, Just } } = require("@aminnairi/lemonade");

const divide = (a, b) => b === 0 ? Nothing() : Just(a / b);

const goodDivision = divide(1, 2)
    .map(x => x + 1)
    .andThen(x => divide(x, 2))
    .map(x => x + 1)
    .withDefault(0);

const badDivision = divide(1, 0)
    .map(x => x + 1)
    .andThen(x => divide(x, 2))
    .map(x => x + 1)
    .withDefault(0);

const anotherBadDivision = divide(1, 2)
    .map(x => x + 1)
    .andThen(x => divide(x, 0))
    .map(x => x + 1)
    .withDefault(0);

console.log(goodDivision);          // 1.75
console.log(badDivision);           // 0
console.log(anotherBadDivision);    // 0

👌 Result

const { Result: { Ok, Err } } = require("@aminnairi/lemonade");

const divide = (a, b) => b === 0 ? Err("division by zero") : Ok(a / b);

divide(1, 2)
    .map(x => x + 1)
    .andThen(x => divide(x, 2))
    .map(x => x + 1)
    .when({ Ok: console.log, Err: console.error })
    // 1.75

divide(1, 2)
    .map(x => x + 1)
    .andThen(x => divide(x, 0))
    .map(x => x + 1)
    .when({ Ok: console.log, Err: console.error })
    // division by zero

divide(1, 0)
    .map(x => x + 1)
    .andThen(x => divide(x, 0))
    .map(x => x + 1)
    .when({ Ok: console.log, Err: console.error })
    // division by zero

divide(1, 0)
    .map(x => x + 1)
    .andThen(x => divide(x, 0))
    .map(x => x + 1)
    .withDefault(-1);
    // -1

👷 Task

const { Task: { Task } } = require("@aminnairi/lemonade");

Task(() => fetch("https://jsonplaceholder.typicode.com/users/1"))
    .map(response => response.json())
    .andThen(({ id }) => Task(() => fetch(`https://jsonplaceholder.typicode.com/posts?userId=${id}`)))
    .map(response => response.json())
    .map(([ post ]) => post.title)
    .when({ Ok: console.log, Err: console.error })
    // sunt aut facere repellat provident occaecati excepturi optio reprehenderit

Task(() => "Hello")
    .map(string => string + " world")
    .andThen((string) => Task(() => string + "!"))
    .when({ Ok: console.log, Err: console.error });
    // "Hello world!"

Task(() => "Hello")
    .map(string => string + " world")
    .andThen(string => Task(() => string + "!"))
    .perform();
    // Promise { <pending> }

Task(() => 1)
    .fork([
        task => task.map(x => x + 1).when({Err: console.error, Ok: console.log}), // 2
        task => task.map(x => x + 2).when({Err: console.error, Ok: console.log}) // 3
    ])
    .when({Err: console.error, Ok: console.log}); // 1

Task X Express

"use strict";

const {Task: {Task}} = require("@aminnairi/lemonade");
const express = require("express");
const fetch = require("node-fetch");

const application = express();
const user = id => Task(() => fetch(`https://jsonplaceholder.typicode.com/users/${id}`));
const postsByUser = id => Task(() => fetch(`https://jsonplaceholder.typicode.com/posts?userId=${id}`));
const responseToJson = response => response.json();

application.get("/users/:id/posts", (request, response) => {
    user(request.params.id)
        .map(responseToJson)
        .andThen(({id}) => postsByUser(id))
        .map(responseToJson)
        .when({
            Err: error => response.status(404).send(error),
            Ok: posts => response.json(posts)
        });
});

application.listen(8080, () => console.log("http://localhost:8080"));

// curl localhost:8080/users/1/posts
// [{...}, {...}, ...]