gistfile1.txt

(define (apply-reduction-relation/generator red t visited?)
  (generator 
   ()
   (let loop ([t t])
     (unless (visited? t)
       (let ([tps (apply-reduction-relation red t)])
         (if (empty? tps)
             (yield t)
             (for-each loop tps)))))
   (yield #f)))

(define (make-hash-visited?)
  (define ht (make-hash))
  (λ (t)
    (if (hash-has-key? ht t)
        #t
        (begin0 #f
                (hash-set! ht t #t)))))