# [Haskell-beginners] A simple function V2

Gary Klindt gary.klindt at googlemail.com
Fri Aug 31 14:06:02 CEST 2012

```Hi,

you don't proof for empty lists, only for empty tails: (x:[])

On 08/31/2012 02:01 PM, Ezequiel Hernan Di Giorgi wrote:
> First i want to thank all the persons who responded me yesterday to help
> me. Thanks! I am so happy with with your friendliness.
> So i have other beginners question:
>
> Now i want a improved version of my* intercalate*. Now i want to call a
> function with two [t][t] and obtain another one which have only
> even elements, even because:
>
>     - [1,2,3,3,4][6] and the ouput [1,6]
>     - [1,2,3,4][5,6,7] output [1,5,2,6,3,7]
>
> I tried it:
>
> *intercalate :: (Eq t) => [t] -> [t] -> [t]*
> *intercalate (x:xs) (y:ys)*
> * | xt == [] = []*
> * | yt == [] = []*
> * | otherwise = x : y : intercalate xs ys*
> * where xt=(x:xs)*
> *            yt=(y:ys)*
>
> but i get nice error
>
> **Main> intercalate [1][6]*
> *[1,6*** Exception: baby.hs:(2,1)-(5,51): Non-exhaustive patterns in
> function intercalate*
> *
> *
> **Main> *
>
> (yes...the file's name is baby.hs)
>
> Thanks in advance! (: (: (:
> (: (:
>
>
>
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