Hi, I have just implemented the function "penultimax" which takes a list of positive integers and produces the "penultimate maximum", that is, the next biggest integer in the list after the maximum. Eg: penultimax [15,7,3,11,5] = 11 One implementation is: penultimax :: [Int] -> Int penultimax ms = foldr max 0 (filter (<msMax) ms) where msMax = foldr max 0 ms But I can think of two variations which might be more efficient: penultimax2 :: [Int] -> Int penultimax2 ms = penultimax2' ms 0 0 where penultimax2' :: [Int] -> Int -> Int -> Int penultimax2' [] p q = q penultimax2' (m:ms) p q | m>p = penultimax2' ms m p | m>q = penultimax2' ms p m | otherwise = penultimax2' ms p q penultimax3 :: [Int] -> Int penultimax3 ms = snd (maxpenmax ms) where maxpenmax :: [Int] -> (Int,Int) maxpenmax [] = (0,0) maxpenmax [m] = (m,0) maxpenmax (m:ms) | m>p = (m,p) | m>q = (p,m) | otherwise = (p,q) where (p,q) = maxpenmax ms How do I work out which is best to use? Is there one clear "winner", or will they each have pros and cons? Thanks, Mark. -- Dr Mark H Phillips Research Analyst (Mathematician) AUSTRICS - smarter scheduling solutions - www.austrics.com Level 2, 50 Pirie Street, Adelaide SA 5000, Australia Phone +61 8 8226 9850 Fax +61 8 8231 4821 Email mark@austrics.com.au