Monads IO

🚀 Efficient Monads for JS: Maybe (Option) and Either (Result)

Why use this lib

1. Small and Tree-Shakable. Either - 3kb minified, Maybe - 3kb minified, can be imported separately
2. No dependencies.
3. Memory-Efficient. 8 bytes overhead per instance (only class pointer)
4. Tested. 100% coverage
5. Practical. Just 2 wrappers: Either and Maybe - easy for non-fp people

Credits

Huge credit to @JSMonk. This library is based on JSMonk/sweet-monads

Docs available in his repository

• Either
• Maybe
• Reference

📦 Installation

• Using npm

  npm i monads-io

• Using Yarn

  yarn add monads-io

• Using pnpm

  pnpm add monads-io

⚙️ Usage

// Real world example
// This maybe is not tree-shakable. Used in NodeJS code
import { Maybe } from "monads-io";

export async function getTargets(
  api: TelegramAPI,
  tokens: formattedText,
  { mentionLimit = 1, message = undefined as message | undefined } = {}
): Promise<Map<number, chat | undefined>> {
  const mentions = getMentions(tokens).slice(0, mentionLimit);

  const targets = new Map<number, chat | undefined>();
  let replyTarget: [number, chat | undefined] | undefined;
  const { messagesService, chatsService } = getServices(api);

  ...

  // 1. Get message
  // 2. Get message reply id (0 = no reply)
  // 3. Get reply message by message id
  // 4. Get reply message sender
  // 5. Get his/her profile
  // 6. Set local variable to profile

  const reply = await Maybe.fromNullable(message)
    .filter((message) => message.reply_to_message_id !== 0)
    .asyncChain((message) =>
      messagesService.getReply(message.chat_id, message.id)
    );

  const sender = await reply
    .map(MemberId.fromMessage)
    .tap(({ memberId }) => {
      replyTarget = [memberId, undefined];
    })
    .asyncChain(({ memberId }) => chatsService.getById(memberId));

  sender.tap((sender) => {
    replyTarget = [sender.id, sender];
  });

  ...

  return replyTarget ? new Map([replyTarget, ...targets]) : targets;
}