#lang eopl

;; interpreter for the LEXADDR language.

(require "lang.rkt")
(require "data-structures.rkt")
(require "environments.rkt")

(provide value-of-translation value-of)

;;;;;;;;;;;;;;;; the interpreter ;;;;;;;;;;;;;;;;

;; value-of-translation : Nameless-program -> ExpVal

(define value-of-translation
  (lambda (pgm)
    (cases program pgm
      (a-program (exp1)
                 (value-of exp1 (init-nameless-env))))))

;; value-of-translation : Nameless-program -> ExpVal
;; Page: 100
(define value-of-program
  (lambda (pgm)
    (cases program pgm
      (a-program (exp1)
                 (value-of exp1 (init-nameless-env))))))

;; value-of : Nameless-exp * Nameless-env -> ExpVal
(define value-of
  (lambda (exp nameless-env)
    (cases expression exp
      (const-exp (num) (num-val num))
      
      (diff-exp (exp1 exp2)
                (let ((val1
                       (expval->num
                        (value-of exp1 nameless-env)))
                      (val2
                       (expval->num
                        (value-of exp2 nameless-env))))
                  (num-val
                   (- val1 val2))))
      
      (zero?-exp (exp1)
                 (let ((val1 (expval->num (value-of exp1 nameless-env))))
                   (if (zero? val1)
                       (bool-val #t)
                       (bool-val #f))))
      
      (if-exp (exp0 exp1 exp2) 
              (if (expval->bool (value-of exp0 nameless-env))
                  (value-of exp1 nameless-env)
                  (value-of exp2 nameless-env)))
      
      (call-exp (rator rand)          
                (let ((proc (expval->proc (value-of rator nameless-env)))
                      (arg (value-of rand nameless-env)))
                  (apply-procedure proc arg)))
      
      (nameless-var-exp (n)
                        (apply-nameless-env nameless-env n))
      
      (nameless-let-exp (exp1 body)
                        (let ((val (value-of exp1 nameless-env)))
                          (value-of body
                                    (extend-nameless-env val nameless-env))))
      
      (nameless-proc-exp (body)
                         (proc-val
                          (procedure body nameless-env)))
      
      (else
       (eopl:error 'value-of 
                   "Illegal expression in translated code: ~s" exp))
      
      )))


;; apply-procedure : Proc * ExpVal -> ExpVal

(define apply-procedure
  (lambda (proc1 arg)
    (cases proc proc1
      (procedure (body saved-env)
                 (value-of body (extend-nameless-env arg saved-env))))))