replacestar.scm

(define replace*
  (lambda (al x)
    (cond
      [(null? x) '()]
      [(symbol? x)
       (cond
         [(assq x al) => cdr]
         [else x])]                         
      [(pair? x)
       (cons (replace* al (car x))
             (replace* al (cdr x)))]
      [(boolean? x) x]
      [(string? x) x]
      [else (error 'replace* (format "unknown expression type: ~a\n" x))])))

(define replace-respect-quote*
  (lambda (al x)
    (cond
      [(null? x) '()]
      [(symbol? x)
       (cond
         [(assq x al) => cdr]
         [else x])]                         
      [(pair? x)
       (if (eq? (car x) 'quote)
           x
           (cons (replace-respect-quote* al (car x))
                 (replace-respect-quote* al (cdr x))))]
      [(boolean? x) x]
      [(string? x) x]
      [else (error 'replace-respect-quote* (format "unknown expression type: ~a\n" x))])))