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, Bulat mailto:Bulat.Ziganshin@gmail.com