I second the suggestion of adding line numbers to error messages. The debugger could also use some improvements.
I am an embedded systems programmer, and I'm quite used to debug using only printf, but the lack of support from Newlisp in this area makes things more difficult than it should be.
Since I'm in the process of butchering....errr, I mean hacking the guts of Newlisp, I took a look at the problem. It doesn't seem easy to do, but it has to be done imho.