Todd, In addition to Matthias' observations:
> (define free-vars-list > (lambda (body) > ( > (if (list? body) (append (free-vars-list (car body)) (free-vars-list > (cdr body))) > (cases expression body > ;; When we have a var-exp, return the variable > (var-exp (id) id) > (primapp-exp (prim rands) (append(free-vars-list > (car rands)) (free-vars-list (cdr rands)))) > (if-exp (test-exp true-exp false-exp) > (append (free-vars-list test-exp) > (free-vars-list true-exp) (free-vars-list false-exp))) > ... There is some confusion here about what body is. Writing down a contract, as done in EOPL, would be helpful to you and to those reading your code. You are testing if body is a list or an expression. Why? It should always be the case that body is an expression. In other words, free-vars-list ought to be a function that processes expressions and calling it with a list ought to be a mistake. I also add the observation that not all vars may be free. Your code seems to assume that when it is called with a var-exp. HTH. -- Cheers, Marco _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
