(load "fin-fun.ss")


(define eval-exp
   (lambda (exp)
     (cond
      ((lit? exp) (lit-datum exp))
      ((varref? exp)(apply-env init-env (varref-var exp)))
      ((app? exp)(apply-proc
		  (eval-exp (app-rator exp))
		  (map eval-exp (app-rands exp))))
      (else (error 'eval-exp
		   "Invalid abstract syntax:"
		   exp)))))

(define the-empty-env (create-empty-ff))

(define extend-env extend-ff*)

(define apply-env
   (lambda (x y)
      (let ([look (apply-ff x y)])
         (if (equal? look 'unknown-symbol)
             (error 'apply-env "undefined symbol " y)
             look))))

(define-record-type prim-proc (fields prim-op))

(define prim-op-names '(+ - *))

(define init-env
   (extend-env
      prim-op-names
      (map make-prim-proc prim-op-names)
      the-empty-env))

(define apply-prim-op
   (lambda (prim-op args)
      (case prim-op
         [(+) (+ (car args) (cadr args))]
         [(-) (- (car args) (cadr args))]
         [(*) (* (car args) (cadr args))]
         [else
          (error 'apply-prim-op
             "Invalid prim-op name: "
             prim-op)])))

(define apply-proc
  (lambda (proc args)
    (cond
      ((prim-proc? proc) (apply-prim-op (prim-proc-prim-op proc) args))
      (else (error 'apply-proc "Invalid procedure: " proc)))))