s c h e m a t i c s : c o o k b o o k

(define search
  (lambda (sym tree)
    (search-path sym
                 tree
                 (lambda (path) path) ;success
                 (lambda ()           ;failure
                   (lambda (t)
                     (error 'not-found "~a" sym)))))

(define search-path
  (lambda (sym tree succ fail)
    (if (symbol? tree)
        (if (eqv? sym tree)
            (succ (lambda (t) t)) ;succeed with trivial result
            (fail))               ;let fail get another crack
        (if (null? tree)
            (fail)                ;let fail try again
            (search-path sym
                         (car tree)
                         (lambda (path) ;success means taking a car
                           (succ (lambda (t) (path (car t)))))
                         (lambda ()     ;failure means searching more ...
                           (search-path sym
                                        (cdr tree)
                                        (lambda (path) ;... with cdring and ...
                                          (succ (lambda (t) (path (cdr t)))))
                                        fail)))))))    ;... failing up

(let ((t 'a))
  ((search 'a t) t))

(let ((t 'a))
  (search 'b t))

(let ((t '(a b c)))
  (map (lambda (x) ((search x t) t)) t))

(let ((t '(((a b c) d (e (f) g)) h))
      (ss '(a b c d e f g h)))
  (map (lambda (x) ((search x t) t)) ss))