Ability to track token locations in input file

[sbc100]

Would it be possible to add some kind of debug mode so that each token could be associated with line and column number in the input file?

I'm writing an tool that processes large s-expressions and it would be nice to report the location where a semantic error occurs.

[jd-boyd]

That would be great if someone wanted to write a pull request for it, but it would be a huge change, so I'm not likely to be the one doing it anytime soon.