I don't know TypeScript, but can't you expend a few lines to write a function 'getA : State -> number?'? Paired with the TypeScript equivalent of Swift's / Rust

I don't know TypeScript, but can't you expend a few lines to write a function 'getA : State -> number?'? Paired with the TypeScript equivalent of Swift's / Rust's if-let, it should be just as convenient.