Quick and Small Haskell Question
Which of the following is better to use?
test1 :: Int -> [Int] test1 k = [x+y | x <-l, x==1, y <-l] where l = [1..k]
with the following result
mihai@keldon:~/tmp$ time ./test 1e7 > /dev/null real 0m9.057s user 0m8.549s sys 0m0.308s
or some monads?
test2 :: Int -> [Int] test2 k = do x <- l guard (x == 1) y <- l return (x+y) where l = [1..k]
mihai@keldon:~/tmp$ time ./test 1e7 > /dev/null real 0m24.057s user 0m23.309s sys 0m0.596s
Both times the main function was:
main = do [d] <- map read `fmap` getArgs let l = test1 d putStrLn $ show l
I’m mainly interested in a quick to code and fast to execute method for a dirty backtracking implementation. (Over 100 variables to be bounded to and over 1500 restrictions). Yet, I’m mainly interested in the aspects behind the scenes which will make one solution better than the other. I want to find out why the list implementation technique is faster that the monadic counterpart. Things like that.