(let ((time-stamp "Time-stamp: <2000-12-11 16:33:59 wand>"))
  (eopl:printf "2-3-3.scm ~a~%" (substring time-stamp 13 29)))

(define-datatype environment environment? 
  (empty-env-record)             
  (extended-env-record
    (syms (list-of symbol?))
    (vals (list-of scheme-value?))
    (env environment?)))

(define scheme-value? (lambda (v) #t))

(define empty-env
  (lambda ()
    (empty-env-record)))

(define extend-env
  (lambda (syms vals env)
    (extended-env-record syms vals env)))

(define apply-env
  (lambda (env sym)
    (cases environment env
      (empty-env-record ()
        (eopl:error 'apply-env "No binding for ~s" sym))
      (extended-env-record (syms vals env)
        (let ((pos (list-find-position sym syms)))
          (if (number? pos)
            (list-ref vals pos)
            (apply-env env sym)))))))