2.09.scm

(define empty-env
  (lambda () '()))

(define extend-env
  (lambda (var val env)
    (cons (list var val) env)))

(define report-no-binding-found
  (lambda (search-var)
    (error 'apply-env "No binding for ~s" search-var)))

(define apply-env
  (lambda (env search-var)
    (if (null? env)
        (report-no-binding-found search-var)
        (if (eqv? search-var (caar env))
            (cadar env)
            (apply-env (cdr env) search-var)))))

(define has-binding?
  (lambda (env s)
    (if (null? env)
        #f
        (if (eqv? s (caar env))
            #t
            (has-binding? (cdr env) s)))))