Monkey.ts

A Monkey Interpreter made in Typescript and Bun.

Install dependencies

bun install

To run:

bun run index.ts

To test:

bun test

About Monkey

Monkey is the programming language described in the book Writing an Interpreter in Go. You might call it an educational programming language, so production-ready interpreters aren’t typically expected—and this one is no exception. However, thanks to Bun, it does come with a few nice features:

• It can run directly without transpiling to JavaScript.
• It can create a standalone REPL executable.

About Monkey.ts

This repository contains a TypeScript implementation of the process laid out in the book. Initially, it was using object-oriented programming. Once I got a working version, I decided to experiment further, and rewrote it. First in a more functional style, and then a full‑blown reactive flavour with Signux. Again, nothing production‑ready, just experiments that were fun to hack on.

Branches at a glance

main  – functional take

• Lexer → plain JS generator (for…of lexer() to get tokens).
• Parser → a bunch of pure Pratt helpers that chew the generator.
• Evaluator → always was a pure function, so I left it mostly untouched.

signux  – functional + FRP

• Same core but every piece talks through Signux events/stores.
• You still pull tokens, but you can also react to them — perfect for live‑coding UIs.
• The parser exposes both a reactive state and a Promise wrapper (await parseProgram()).

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Why bother?

Because:

• I wanted an excuse to practise FP/FRP in a tiny codebase.
• Generators keep memory low and make REPL streaming super easy.
• Signux lets me time‑travel debug the interpreter. Although this has not been implemented, the Lexer would allow it easily. Nerdy, but neat.