[Jscheme-devel] function for finding a list's tail?

[Kyle R. B. <kyl...@gm...>]

Is there a built-in for finding a list's tail?

I've implemented 2 versions, one in jscheme:

(define-method (tail (lst
Pair))

  (let loop ((lst
lst))


(cond

     ((null?
lst)


#f)

     ((null? (cdr
lst))


lst)


(else

      (loop (cdr lst))))))


and one in java:


/**

   * Finds a list's tail by traversing the
list.

   * @param lst the list to find the tail
of

   * @error ClassCastException if lst is not a proper
list.

*/

  public static Pair tail (Pair lst)
{

    Object tmp =
rest(lst);

    while (isPair(tmp))
{

      lst =
(Pair)tmp;

      tmp =
rest(tmp);


}

    return
lst;

  }


The java version is quite a bit faster:

(define
*1k-list*

  (let loop ((max 1000) (res
(list)))

    (cond ((= 0
max)


res)


(else

           (loop (- max 1) (cons max
res))))))



(time

 (dotimes (ii
1000)

   (my-tail
*1k-list*)))


$7 = (() (479 msec) (147624 bytes))


(time

 (dotimes (ii
1000)

   (U.tail *1k-list*)))

$8 = (() (42 msec) (189360 bytes))


Is it ok if I add that method as a static to the utils and add unit tests?

Thanks,

Kyle