Can you re-define car and cdr for your "given scheme program" --
e.g. load it into an environment in which car is a procedure that
increments your meter before calling the real thing?
This is a possibility. However I thought it will be better -
performance wise - if I could modify the C-routine directly. I am still
a newbie to Scheme/mit-scheme and not very sure if modifying C will
actually be faster than modifying user program.
Who-all's use of car and cdr do you want to measure? Surely not the
whole system... ?