Right cause the boolean isn't a named type. If you have two possible states that can be represented with a boolean, or an enum of the two possible states which embeds more info into the callsite

Yeah I do wonder if we need an easier way to declare these things because programmers are lazy and even in Rust I wouldn't always bother.

You can kind of do it in Typescript with strings:

function create_user(role: "admin" | "normal")

But of course the downside is they are strings at runtime. I'm sure it's possible though.