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>>>>> On Mon, 4 Jan 1999 10:24:52 -0600 (CST), Shriram Krishnamurthi <shriram@xxxxxxxxxxx> said:
> Harvey J. Stein wrote:
>> Maybe better than list-length>= would be (list-ref-with-default l n
>> default-value, which returns default-vaule if (>= (length l) n).
> That doesn't mean the programmer will know what value to provide --
> indeed, this increases the possibility of error. To be safe, in the
> worst case, he would have to scan the entire list to make sure the
> default-value isn't in it (remember, Scheme doesn't have a
> generative struct mechanism either), or tack a token onto every
> value already in the list. Clearly, neither of these is viable.
(let* ((sentinel (cons 0 0))
(value (list-ref-with-default l n sentinal)))
(if (eq? value sentinel)
...not found...
...found...))
But I agree that continuations are cleaner.
../Dave