Hi, I defiend the following function to get the last element of a list: final [a] = a final (_:t) = final t and it works as expected. Since I didn't want to have a non exhaustive pattern, I added the following case: final [] = [] - I consider that the end of an empty list is the empty list final [a] = a final (_:t) = final t Suddenly, the function stoped working with a rather cryptic (for a newbie at least) error message: *Temp> final [4,5] <interactive>:1:9: No instance for (Num [a]) arising from the literal `5' at <interactive>:1:9 Possible fix: add an instance declaration for (Num [a]) In the expr*Temp> ession: 5 In the first argument of `final', namely `[4, 5]' In the expression: final [4, 5] What have I done so wrong? Thanks in advance, Fernando