Lich - Chaining computations in TypeScript

Lich is a library for chaining computations in TypeScript. It's heavily inspired by the monadic structures in Haskell. In particular Maybe and Either. The goal of lich is to improve flow, safety and reliability of your code.

Installing

Via npm:

$ npm install @quanterall/lich

Via yarn:

$ yarn add @quanterall/lich

Via html:

<script src="https://unpkg.com/@quanterall/[email protected]/dist/index.web.js"></script>

and then use via Lich like so:

<script>
  const maybe = Lich.Just(10);
  const either = Lich.Right("hello world");
</script>

How does it work?

Let's say you want to apply several functions to a string, but you only want to work with it, if it's not empty at the end of each one of them? This is how you may go about it, using lich:

import { Maybe, Just, Nothing } from "lich";

export function parseString(s: string): Maybe<string> {
  return safeTrim(s)
    .map((j) => j.toUpperCase())
    .bind(removePs) // Maybe remove the 'p's in the text.
    .bind(clearSpaces); // Maybe clear up the spaces.
}

function safeTrim(s: string): Maybe<string> {
  const trimmed = s.trim();
  if (trimmed.length === 0) return Nothing();

  return Just(trimmed);
}

function removePs(s: string): Maybe<string> {
  const res = s.replace(/p/g, "");
  if (res.length === 0) return Nothing();

  return Just(res);
}

function clearSpaces(s: string): Maybe<string> {
  const res = s.replace(/ +/g, " ").trim(); // We want only one space between words
  if (res.length === 0) return Nothing();

  return Just(res);
}

If you care about in which step things went wrong you can use Either to track your errors:

import { Either, Right, Left } from "lich";

export function parseString(s: string): Either<string, string> {
  return safeTrim(s)
    .map((j) => j.toUpperCase())
    .bind(removePs) // Either remove the 'p's in the text or return a `Left` with a reason.
    .bind(clearSpaces) // Either clear up the spaces or return `Left` with a reason.
    .onLeft((l) => console.error(l)); // Log the error to the console
}

function safeTrim(s: string): Either<string, string> {
  const trimmed = s.trim();
  if (trimmed.length === 0) return Left("Error in 'safeTrim': String is empty");

  return Right(trimmed);
}

function removePs(s: string): Either<string, string> {
  const res = s.replace(/p/g, "");
  if (res.length === 0) return Left("Error in 'removePs': String is empty");

  return Right(res);
}

function clearSpaces(s: string): Either<string, string> {
  const res = s.replace(/ +/g, " ").trim(); // We want only one space between words.
  if (res.length === 0) return Left("Error in 'clearSpaces': String is empty");

  return Right(res);
}

A more deep comparison against other error handling practices could be found here.

Documentation

• Maybe
  • Just
  • Nothing
  • map
  • bind
  • fold
  • mapAsync
  • bindAsync
  • foldAsync
  • otherwise
  • onJust
  • onNothing
  • isJust
  • isNothing
  • toEither
• Either
  • Right
  • Left
  • map
  • bind
  • fold
  • mapAsync
  • bindAsync
  • foldAsync
  • otherwise
  • onRight
  • onLeft
  • fromRight
  • fromLeft
  • isRight
  • isLeft
  • toMaybe