'any' and 'all' compared with the rest of the Report
Tue, 23 Jan 2001 23:10:53 +0100
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.
or = foldr (||) False
any p = or . map p
ghc -O generates basically the following code (use -ddump-simpl to
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
> 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
hit at all.