Hah this is a classic. I actually used this as a reference to build my own about a year ago in typescript (documentation a long way to go and still WIP) which

Hah this is a classic. I actually used this as a reference to build my own about a year ago in typescript (documentation a long way to go and still WIP) which I am using in a couple of production ready dsls: https://github.com/panyam/tlex https://github.com/panyam/tlex