/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.

>>26
Alright, s-exps are unsuitable for even the simplest intelligent codewalking. Which is a necessary condition for writing useful code transforms.

Transforming untagged nodes and hoping that the result will be correct runnable code is like putting grenades in your barbecue and hoping that no one gets hurt.