More.

08-barf/main.rkt

@@ -272,9 +272,13 @@ CFG for the BARF language:
                                               (if (string=? name fname) (f) (#f))])))]))
   (if (not foundfun) (error 'findfun "Function not found.") foundfun))
 
-(: eval : PROGRAM -> Primitive)
-;; evaluates PROGRAM expressions by reducing them to numbers
-(define (eval expr)
+(: eval : PROGRAM BARF -> Primitive)
+; Evaluates a BARF in the context of a PROGRAM.
+(define (eval prog expr)
+  (let ([eval (lambda ([e : BARF]) (eval prog e))]
+        [eval-number (eval prog e)]
+        [eval-boolean (eval prog e)])
+
   (cases expr
          [(Num n) n]
          [(Bool p) p]
@@ -298,9 +302,10 @@ CFG for the BARF language:
               (error 'eval "Can't create parameter binding to reserved name '~s'." par)
               (list (Par par) (Body body)))]
          [(Call f arg) (eval-call (value->barf (eval f)) arg)]
-         [(Id name) (error 'eval "free identifier: ~s" name)]))
+         [(Id name) (error 'eval "free identifier: ~s" name)])))
 
 (: run : String -> Primitive)
 ;; evaluate an BARF program contained in a string
 (define (run str)
-  (eval (parse str)))
+  (eval (parse str) (Call2 'main (Num 4))))
+