On Thu, Dec 24, 2009 at 1:24 PM, samppi <[email protected]> wrote:
> I'm having trouble with figuring out something. First, to get the
> first element of a sequence so that (pred element) is false, you do
> (first (drop-while pred sequence)). This is lazy, and stops
> immediately when the element is found.
>
> Now, I want to get the element *right before* the element returned by
> (drop-while pred sequence)). I could use reduce, but that is non-lazy
> and always goes through the entire sequence. The sequences I'm working
> with are very big. So, is there a lazy way to get the element right
> before the first element that doesn't fulfill the predicate? Thanks in
> advance.
(some
(fn [[a b]] (when (odd? b) a))
(partition 2 1 [2 4 6 8 9 10 11])))
;=> 8
--Chouser
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