I am designing one, aimed at Claude Code and other AI Coding Agents, and getting the first version lex/parser/compiler was an afternoon project. It was initially a TypeScript toolchain generating TypeScript code.

I keep adding things here and there, a couple hours everyday. Then after about a week I decided to switch the toolchain from TypeScript to Rust, how much work? A 5 minute planning session and a ~20 minutes implementation phase.

Trivial stuff indeed.