Hi Gilberto,
On Wed, Mar 30, 2011 at 4:39 PM, Gilberto Garcia
fkSum :: Int -> [Int] -> Int fkSum a [] = 0 fkSum a (b) = foldl (+) 0 (filter (\x -> isMultiple x b) [1..a])
isMultiple :: Int -> [Int] -> Bool isMultiple a [] = False isMultiple a (x:xs) = if (mod a x == 0) then True else isMultiple a xs
You can make both these functions a little bit more efficient by making them strict in the first argument, like so: {-# LANGUAGE BangPatterns #-} fkSum :: Int -> [Int] -> Int fkSum !a [] = 0 fkSum a (b) = foldl (+) 0 (filter (\x -> isMultiple x b) [1..a]) isMultiple :: Int -> [Int] -> Bool isMultiple !a [] = False isMultiple a (x:xs) = if (mod a x == 0) then True else isMultiple a xs This change ensures that the first argument is always evaluated. Before `fkSum undefined []` would return 0, now it results in an error. The upside is that when a function is strict in an argument, GHC can use a more efficient calling convention for the function. In this case it means that instead of passing the first argument as a pointer to a machine integer, it can pass the machine integer directly (in a register). This optimization is particularly worthwhile for accumulator parameters. Johan