json-e

Pratt-parsers is a very underrated style of parsing. Years ago when I was at Mozilla we built PrattParser utils in JS: https://github.com/taskcluster/json-e/blob/386ae415d807eb066... It probably had short comings, because it's been rewritten since (I haven't kept up). But with a few rules and simple functions a pratt parser is rather intuitive, and easy to write and port to other languages. I'd be very curious to see the next article :)

I needed a templated language recently (couldn’t do with Mustache methods). Looked at jsonnet but it looked quite abandoned. Ended up finding Json-E [0]. Pretty powerful, and give you the option to pass in methods to the context as to expose them. No support for Async methods, but I wrapped around it with some Promises and did the trick. [0] https://github.com/taskcluster/json-e

I prefer https://github.com/taskcluster/json-e Has the advantage/disadvantage that it's still valid json/yaml I wrote a scary command line wrapper for it: https://wryun.github.io/rjsone/ Has libs for Python, Go, and JS, and there's a bazel interface.

I recently needed a custom expression language and using a Pratt-Parser to write the interpreter was a joy. https://github.com/taskcluster/json-e/blob/a0ab770157a5fdb5d... I wrote up abstractions so you just declare token patterns, precedence ordering of tokens, and infix/prefix rules as mapping from token to function(token, ctx). Where ctx.attempt(...token)), ctx.require(...token) and ctx.parse(precedence) is all you need to implement almost anything. I didn't get as far as to make it recursive and support multiple grammars. But I'm sure this concept can be made very elegant, without too many tricks.