Lisp Code Walker Challenges

HomoiconicExampleInManyProgrammingLanguages stated, that it were trivial to implement a code walker in LispLanguage, which replaced every expression with a call to some timing function and a subsequent call to the original expression.

Please note, that unquoted expressions suffice. Quoted expression need not be taken care of, because (in the intended use of this code) they will be handled on demand by a customized version of eval.