[Haskell-cafe] Empty Input list

Dear Haskell friends, what can I do, if a function gets an empty input list? I want, that it only returns nothing. This is my source code: tmp:: [(Int, Int)] -> Int -> (Int, Int) tmp (x:xs) y | y == 1 = x | y > 1 = tmp xs (y-1) If this function gets an empty list, he throws "Exception: sortAlgo.hs:(18,1)-(21,44): Non-exhaustive patterns in function Main.tmp" *Main> tmp [(1,2),(3,2)] 1 (1,2) *Main> tmp [(1,2),(3,2)] 2 (3,2) *Main> tmp [] 1 *** Exception: sortAlgo.hs:(20,1)-(22,44): Non-exhaustive patterns in function Main.listElementIntInt Thank you for any help ! Best regards Kevin