Chapter 3 stub.

chap3.rkt

@@ -0,0 +1,10 @@
+(define (find-symbol id tree)
+  (call/cc
+   (lambda (exit) 
+     (define (find tree)
+       (if (pair? tree)
+           (or (find (car tree)) (find (cdr tree)))
+           (if (eq? tree id) (exit #t) #f)))
+     (find tree))))
+           
+