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
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