Re: [Haskell-cafe] Code review: efficiency question
Bulat Ziganshin wrote: [ideas including reverseMapM_] you will laugh, but speed of your two solutions depends on so many factors (including size of CPU cache) that noone can say that is better in general. although for small lists reverseMapM_ should be faster than reverse+mapM. what will be faster - using of higher-order function or direct recursion, i can't say, it's a really counter-intuitive area of ghc optimizer :) of course, i don't think that all that really matters for your program (drawing should anyway need much more time than looping). just use higher-level approach (that makes code simpler to write, understand and maintain) and don't bother your mind :) Hi Bulat! Thanks for the suggestions about reverseMapM_ etc. It seems that since the speeds of the two solutions can be relatively faster/slower on different platforms/CPUs I might as well just use the combination of existing functions mapM_ and reverse at the moment to get readable code with the least amount of effort :-) Best regards, Brian. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Code review: efficiency question
Brian, You might also want to take a look at the list fusion functionality in GHC which often can help optimize your programs when programming with lists. http://www.haskell.org/ghc/docs/latest/html/users_guide/rewrite-rules.html#id3153234 It doesn't help in your particular program but it might be usable for you in the future. Cheers, /Josef On 5/3/06, Brian Hulley [EMAIL PROTECTED] wrote: Bulat Ziganshin wrote: [ideas including reverseMapM_] you will laugh, but speed of your two solutions depends on so many factors (including size of CPU cache) that noone can say that is better in general. although for small lists reverseMapM_ should be faster than reverse+mapM. what will be faster - using of higher-order function or direct recursion, i can't say, it's a really counter-intuitive area of ghc optimizer :) of course, i don't think that all that really matters for your program (drawing should anyway need much more time than looping). just use higher-level approach (that makes code simpler to write, understand and maintain) and don't bother your mind :) Hi Bulat! Thanks for the suggestions about reverseMapM_ etc. It seems that since the speeds of the two solutions can be relatively faster/slower on different platforms/CPUs I might as well just use the combination of existing functions mapM_ and reverse at the moment to get readable code with the least amount of effort :-) Best regards, Brian. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Code review: efficiency question
Evan Martin wrote: I remember reading a tutorial that pointed out that you can often avoid explicit recusion in Haskell and instead use higher-level operators. For your code, I think drawModals = foldr (flip ()) (return ()) . map drawModal works(?). I think it would be foldl so that the (return()) would be nested as the leftmost element. Thanks for pointing out this point-free version of drawModals, although for readability at the moment I think I still prefer just to use mapM_ drawModal (reverse cs) Best regards, Brian. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Code review: efficiency question
Hello Brian, Tuesday, May 2, 2006, 3:12:48 AM, you wrote: -- Prolog style coding... drawModals :: [Control] - ManagerM () drawModals [] = return () drawModals (c:cs) = do drawModals cs drawModal c imho, it's typical functional style, but without using higher-level functions mapM_ drawModal (reverse cs) However, while this looks more elegant, it is less efficient? In other words, how much optimization can one assume when writing Haskell code? ghc will don't translate your later code into the former one. although in general ghc (but not other haskell compilers, afaik) is very good in replacing one code with another faster one and in particular in translating list producer + list consumer into straightforward loop how about this solution: reverseMapM_ f (x:xs) = do reverseMapM_ f xs; f x reverseMapM_ f [] = return () or you can define `reverseMapM_` via fold, if you have better FP skills than me :) I'm trying to get a rough idea so I can decide whether to write helper functions such as drawModals in future or whether I should always just use the most elegant code instead. Any ideas? you will laugh, but speed of your two solutions depends on so many factors (including size of CPU cache) that noone can say that is better in general. although for small lists reverseMapM_ should be faster than reverse+mapM. what will be faster - using of higher-order function or direct recursion, i can't say, it's a really counter-intuitive area of ghc optimizer :) of course, i don't think that all that really matters for your program (drawing should anyway need much more time than looping). just use higher-level approach (that makes code simpler to write, understand and maintain) and don't bother your mind :) -- Best regards, Bulatmailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
