[Haskell-cafe] Ultra-newbie Question

[Ivan Lazar Miljenovic]

On 18 September 2010 17:51, Christopher Tauss <ctauss1 at gmail.com> wrote:
> Hello Haskell Community -
>
> I am a professional programmer with 11 years experience, yet I just do not
> seem to be able to get the hang of even simple things in Haskell.  I am
> trying to write a function that takes a list and returns the last n
> elements.
>
> There may be a function which I can just call that does that, but I am
> trying to roll my own just to understand the concept.
>
> Let's call the function n_lastn and, given a list  [1,2,3,4,5], I would like
> n_lastn 3 = [3,4,5]
>
> Seems like it would be something like:
>
> n_lastn:: [a]->Int->[a]
> n_lastn 1 (xs) = last(xs)
> n_lastn n (x:xs) = ????
>
> The issue is I do not see how you can store the last elements of the list.

Easiest way I can think of:

n_lastn n = reverse . take n . reverse

Alternatively:

n_lastn n xs = drop (len - n) xs
    where
        len = length xs

-- 
Ivan Lazar Miljenovic
Ivan.Miljenovic at gmail.com
IvanMiljenovic.wordpress.com