I'm pretty sure I have exactly what you are talking about. error handeling was one of the things that I wanted to get right with jaithon, and I made my system similar to like rust.
error[E0301]: cannot assign to immutable binding `x` --> examples/demo.jai:7:5 | 5 | let x = 1 | - `x` declared immutable here ... 7 | x = 2 | ^^^^^ assignment to immutable binding | help: change the declaration to `var x = 1`
^^ That was shown from the Readme, more extensive examples are in documentation!
Is this what you were refering to or something else, I completely agree that erorr handeling is very important.