Result and the question mark operator

Recoverable errors are values: Result<T, E>. The ? operator either unwraps Ok(T) or returns the Err(E) early from the current function. Planned exercises: 1. choose Result<T, E>. 2. recognise Ok and Err. 3. choose ? over nested matches for propagation. 4. fill an Ok(value). 5. fill a function return type. 6. write a parser helper. 7. write a function with two ? calls. 8. translate TS throw/catch code. 9. fix a function whose return type cannot use ? yet.