Good error reporting is crucial in programming languages. Doing it at compile time was easy in ArkScript as we have all the context we need at hand, but since we compile code down to bytecode, which is then run by the virtual machine, we loose a lot of context: the source files, their path, their content, we don’t have that anymore! Our runtime errors could only show the VM internal state. This article is about how it all changed.\n

ArkScript is an interpreted/compiled language since it runs on a VM. For a long time, runtime error messages looked like garbage, presenting the user with an error string like “type error: expected Number got Nil” and some internal VM info (instruction, page, and stack pointers). Then, you had to guess where the error occurred.

I have wondered for a long time how that could be improved, and I only started working on that a few weeks ago. This post is about how I added source tracking to the generated bytecode, to enhance my error messages.