anuraghazra/typelevel-parser

What the hell is this?

This is my experiment to push the limits of TypeScript's type system by writing a "real" tokenizer/parser/interpreter entirely on type-level.

My goal was to write a DSL to query structured objects.

It's quite similar to how lodash.get syntax works but with a bit more flare, where you can do array index access, use $where() clauses & extract/filter the data from nested objects.

Features

• Dot Access
• Array Access
• $where() clause
• Deeply nested access / chaining and all that jazz
• Support for proper syntax/parser errors

Demo

Use TSPlayground

Or clone this repo and open demo.ts file to explore the wonders!

You can also open each of the modules separately to see how the tokenizer, parser and interpreter works, I've added small demos on each time.

Syntax

Dot Access

Dot access is the most basic way to access nested elements, similar to lodash.get()

type Demo1 = Run<typeof obj, "this.is.dot.access">;

Arrays

There are two ways to access arrays,

1. Index access: where you specify which index you want eg: comments[0]
2. Bulk access: where you don't specify the index and thus get the whole array as union. eg: comments[]

type Demo1 = Run<typeof obj, "comments[0]">;
type Demo2 = Run<typeof obj, "comments[]">;

Where clause

Using $where() clause you can filter out elements from array by their properties.

$where() can accept multiple comma separated value too.

type Demo1 = Run<typeof obj, "users[].$where(id:3,age:20)">;

But WHY?

Because it's fun! I love to experiment with type level code and explore ways to push the limits of the type system. I just love esoteric programming.

Should I use this in production?

!YES

Why even write a tokenizer/parser to do this when you can also do the same with template literal types?

Like how Haz did here

Because I wanted to:

• Support proper syntax errors.
• Additional complex syntaxes like $where() clause.
• Also it's fun.