Iavor Diatchki wrote:
[...] but in practise programs run slower.
If "practise" = "simple interpreter", yes. But...
this is where i would expect a good compiler to do some optimisation, i.e to remove the need for the intermediate list.
<TotallyUnbiasedAd> Given or = foldr (||) False any p = or . map p ghc -O generates basically the following code (use -ddump-simpl to see this): any :: (a -> Bool) -> [a] -> Bool any p xs = let go ys = case ys of (z:zs) -> case p z of False -> go zs True -> True in go xs This is exactly the recursive version, without any intermediate list, but I hardly think that anybody recognizes this with a quick glance only. </ToTallyUnbiasedAd>
i like the idea of programming at a higher level, as i believe it produces "better structured" programs. what i mean is that one manages to capture certain aspects of a program, which would be obscured if one always used explicit recursion. i think higher order functions like maps and folds really go a long way toward structuring functional programs. in a way this is simillar to using loops instead of explicit gotos in procedural programs. anyways these are my deep thought on the matter :)
IMHO you should write any kind of recursion over a given data structure at most once (in a higher order function). (Constructor) classes and generics are a further step in this direction. It vastly improves readability (after you get used to it :-) and often there is no performance hit at all. Cheers, Sven