(define-datatype continuation continuation?
  (halt-cont)
  (proc-cont
   (cont continuation?))
  (let-cont
   (syms (list-of symbol?))
   (bodies (list-of expression?))
   (env anything?)
   (cont continuation?))
  (eval-bodies-cont
   (exps (list-of expression?))
   (cont continuation?)
   (env anything?))
  (change-cont
   (sym symbol?)
   (env anything?)
   (cont continuation?))
  (cons-cont
   (v anything?)
   (cont continuation?))
  (eval-exps-cont
   (ls list?)
   (cont continuation?)
   (env anything?))
  (if-cont
   (true-exp expression?)
   (false-exp expression?)
   (cont continuation?)
   (env list?)))


(define apply-cont
  (lambda (cont val)
    (cases continuation cont
	   [halt-cont ()
		      (pretty-print val)]
	   [change-cont (sym env cont)
			(apply-cont cont (change-env env sym val))]
           [proc-cont (cont)
		      (apply-primitive-procedure (cadar val) (cdr val) cont)]
           [let-cont (syms bodies env cont)
		     (eval-bodies bodies cont (extend-env syms val env))]
	   [cons-cont (v cont)
		      (apply-cont cont (cons v val))]
           [eval-bodies-cont (exps cont env)
			     (eval-bodies exps cont env)]
	   [eval-exps-cont (ls cont env)
			   (eval-expressions-cps ls (cons-cont val cont) env)]
	   [if-cont (true-exp false-exp cont env)
		    (if val
			(eval-expression true-exp cont env)
			(eval-expression false-exp cont env))])))