G'day all.
Quoting Brian Hulley
Hi - I started off writing the following piece of monadic code:
let drawModal :: Control -> ManagerM () drawModal c = do -- details omitted
-- Prolog style coding... drawModals :: [Control] -> ManagerM () drawModals [] = return () drawModals (c:cs) = do drawModals cs drawModal c drawModals cs
then it struck me that I should have not bothered with drawModals and instead should just have used:
mapM_ drawModal (reverse cs)
However, while this looks more elegant, it is less efficient?
I suspect it depends how long the list is. The original drawModals would probably be more efficient for small lists, because it doesn't require creating an intermediate list. OTOH, it may well be less efficient for longer lists because it can't take advantage of tail recursion.
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.
This is a question that is independent of Haskell. You should ALWAYS write the most elegant code first, and only make it uglier if it's not fast enough. (Note: Some programs are non-Knuthian in that they do require attention to efficiency before writing any code. But even then, it's usually worth putting effort into designing a good API first. That way, you can write the elegant code first, and if/when you have to replace it later, the good API insulates the rest of the code from the change.) Cheers, Andrew Bromage