On Jan 3, 9:22 pm, Timothy Pratley <timothyprat...@gmail.com> wrote:
> 2010/1/4 Tom Hicks <hickstoh...@gmail.com>:
>
> > All the other code is there to parallel the functionality in 'subvec'.
>
> Ah right, I see what you mean.
> Calling count in the two argument form will realize the entire
> sequence unnecessarily. Take and drop are already lazy so no need to
> call lazy-seq... so if you wanted to explicitly return nil for invalid
> indices you could still simplify to:
> (defn indexed-subseq
> ([coll start]
> (when (not (neg? start))
> (drop start coll)))
> ([coll start end]
> (when (and (not (neg? start)) (<= start end))
> (take (- end start) (drop start coll)))))
> ; (indexed-subseq [0 1 2 3 4] 1 3)
> ; = (1 2)
> ; (indexed-subseq [0 1 2 3 4] -5 3)
> ; = nil
> ; (indexed-subseq [0 1 2 3 4] 4 3)
> ; = nil
> ; (indexed-subseq [0 1 2 3 4] 2)
> ; = (2 3 4)
>
> Regards,
> Tim.
Very cool, thank-you....this is exactly the kind of feedback
that's valuable as I learn to "think in Clojure". For a second
I wondered why your version didn't need the seq call to
insure that the argument was a sequence but then realized
that, since we were calling only drop and take, they will handle it.
I've updated the gist to reflect the latest version. Thanks again for
your help.
regards,
-tom
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