main :: [sys_message]
main = [Stdout h27m, Stdout biggestm]
       where h27  = hailstone 27
             h27n = #h27
             h27f = take 4 h27
             h27l = drop (h27n - 4) h27
             h27m = "The hailstone sequence for 27 has " ++
                    show h27n ++ " elements starting with " ++
                    show h27f ++ " and ending with " ++
                    show h27l ++ "\n"

             range = [1..100000]
             biggest = max [#hailstone n | n<-range]
             nbiggest = hd [n | n<-range; #hailstone n = biggest]
             biggestm = "The number with the longest Hailstone " ++
                        "sequence < 100.000 is " ++ show nbiggest ++
                        " with length " ++ show biggest ++ "\n"

hailstone :: num->[num]
hailstone = (++[1]) . takewhile (>1) . iterate step
            where step n = (3 * n) + 1, if n mod 2 = 1
                         = n div 2, otherwise