프레임은 일관된 패턴 바인딩만 기록한다.

(begin
  (define (variable? pattern)
    (and (pair? pattern) (eq? (car pattern) '?)))
  (define (extend-if-consistent variable value frame)
    (let ((found (assoc (cadr variable) frame)))
      (cond (found
             (if (equal? value (cdr found)) frame 'failed))
            (else
             (cons (cons (cadr variable) value) frame)))))
  (define (pattern-match pattern datum frame)
    (cond ((eq? frame 'failed) 'failed)
          ((variable? pattern)
           (extend-if-consistent pattern datum frame))
          ((and (pair? pattern) (pair? datum))
           (pattern-match
             (cdr pattern)
             (cdr datum)
             (pattern-match (car pattern) (car datum) frame)))
          ((equal? pattern datum) frame)
          (else 'failed)))
  (define frame
    (pattern-match '(parent (? who) (? child))
                   '(parent bob alice)
                   '()))
  (list (cdr (assoc 'who frame))
        (cdr (assoc 'child frame))))