How would you guys memoize the following code. simpleCalc :: (Int,Int) -> (Int,Int) simpleCalc (1,l) = (1,l+1) simpleCalc (x,l) | (odd x) = simpleCalc (((3*x) + 1), 1 + l) | otherwise = simpleCalc ((x `div` 2), 1 + l) sCalc x = simpleCalc (x,0) sCalcListRange a b = map sCalc [a..b] sCalcListLengthRange a b = map snd (sCalcListRange a b) The key is I need to calculate maximum (sCalcListLengthRange 1 1000000). This is a common programming contest problem that I'm playing with for fun. My first attempt fails miserably. It begins to thrash much more quickly then simple version above: calcListLengthRange a b = map snd (calcListRange a b) calcListRange a b = map calcList [a .. b] where calcList = ((map calc' [0 ..]) !!) where calc' :: Int -> (Int,Int) calc' i = calcList' (i,0) calcList' :: (Int,Int) -> (Int,Int) calcList' (1,l) = (1,l+1) calcList' (x,l) | (odd x) = ((fst((calcList ((3*x) + 1))), snd(calcLi\ st((3*x) + 1)) + 1 + l)) | otherwise = ((fst((calcList (x `div` 2))), snd(calcLi\ st((x `div` 2))) + 1 + l)) I tried to associate a table entry with a particular solution to the problem, so taht calcList would just be a lookup for those we had finished calculating. Sorry this code is ugly I know, but I'm just learning. Cheers, Bryce