import { recursive } from "https://deno.land/x/ts_matches@v5.4.0/mod.ts";
Must pass the shape that we expect since typescript as of this point can't infer with recursive functions like this.
Parameters
fn: EnsurredType<B>
This should be a function that takes a parser, basically the self in a type recursion, and return a parser that is the combination of the recursion.