I have found that this advice doesn't work too well when dealing with large, preferably legacy, codebases along with a pile of third-party libraries. Sometimes, the best debugger is a debugger.
A-men. Right now, I'm waist-deep in over 80k lines of JavaScript neither I nor anyone remaining on our team wrote, and just being able to set breakpoints on event listeners in Chrome and step into the functions that are fired probably saved me weeks off a more plodding read-through-the-whole-codebase approach.
I'm not sure how you'd create a language that would solve that problem, though I guess since the bug I was chasing down was a classic state problem, maybe it would have been caught by a compiler in Fay/Haskell.
