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Functional

Common Functional Programming Algebraic data types for JavaScript that is compatible with most modern browsers and Deno.

Usage

This example uses the Ramda library - for simplification - but you should be able to use any library that implements the Fantasy-land specifications.

import { compose, converge, lift, map, prop } from "https://x.nest.land/ramda@0.27.0/source/index.js";
import Either from "https://deno.land/x/functional@v0.5.0/Either.js";
import Task from "https://deno.land/x/functional@v0.5.0/Task.js";

const fetchUser = userID => Task.wrap(_ => fetch(`${URL}/users/${userID}`).then(response => response.json()));

const sayHello = compose(
  converge(
    lift((username, email) => `Hello ${username} (${email})!`),
    [
      map(prop("username")),
      map(prop("email"))
    ]
  ),
  fetchUser
);

// Calling `sayHello` results in an instance of `Task` keeping the function pure.
assert(Task.is(sayHello(userID)));

// Finally, calling `Task#run` will call `fetch` and return a promise
sayHello(userID).run()
  .then(container => {
    // The returned value should be an instance of `Either.Right` or `Either.Left`
    assert(Either.Right.is(container));
    // Forcing to coerce the container to string will show that the final value is our message.
    assert(container.toString(), `Either.Right("Hello johndoe (johndoe@gmail.com)!")`);
  });

// await sayHello(userID).run() === Either.Right(String)

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