Ah, so it's a change in ac.scm ? Hmm. Just out of curiousity, do you think you could do this just in the 'do macro? Although you do lose the ability to do that in the function body. Hmm.
Also, since this feature hijacks some valuable characters, it would need to be applicable for far more situations than just 'do, or it would be a waste. I believe it fulfills this requirement.