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! (: (: (: (: (: