[racket] Enhancing a macro

I've just come across Jay McCarthy's blog series on continuation marks
where he uses this exact problem (keeping track of indentation level)
to illustrate the use of dynamic-wind, parameters, and continuation
marks.

http://jeapostrophe.github.com/blog/2012/07/16/cont-marks/
http://jeapostrophe.github.com/blog/2012/07/25/cont-marks2/
http://jeapostrophe.github.com/blog/2012/07/30/cont-marks3/

Harry Spier