adding missing defn for append

simulator-primitives.rkt

@@ -116,6 +116,7 @@
                                                     
                                                      symbol->string
                                                      string-append
+                                                     string-length
                                                      
                                                      (my-cons cons)
                                                      (my-list list)

tests/conform/program0.sch

@@ -37,6 +37,12 @@
       (add1 (length (cdr l)))))
 
 
+(define (append l1 l2)
+  (if (null? l1) 
+      l2
+      (cons (car l1) (append (cdr l1) l2))))
+
+
 (define vector-copy
   (lambda (v)
     (let ((length (vector-length v)))