/prog/ challenge

Write a macro that, given a term of code, transforms all the calls to the function FOO in that term, and only those calls, into calls to function BAR with the same arguments.
Language: Common Lisp or Scheme.

>>30
He is not correct. A call to macro zoo is not a call to function foo. The challenge is to transform just the direct calls to a function, without interfering with the inner workings of any functions or macros (it's called "information hiding"). Besides, once you can target exclusively the direct calls, it would be trivial to call macroexpand first and then to call our macro.