;; scanとenv-loopを抜き出す． ;; 見つかった時の手続きをprocで渡す． (define (scan var vars vals proc) (cond ((null? vars) #f) ((eq? var (car vars)) (proc var vars vals)) (else (scan var (cdr vars) (cdr vals) proc)))) (define (env-loop var …

;; フレームを束縛のリストとして表現 (define (make-frame variables values) (map cons variables values)) (define (first-binding frame) (car frame)) (define (rest-bindings frame) (cdr frame)) (define (binding-variable binding) (car binding)) …