Am 24.09.2010 16:53, schrieb Daniel Fischer: [...]
However, I benchmarked some more today, and the results suggest that
intersperse :: a -> [a] -> [a] intersperse _ [] = [] intersperse s (x:xs) = x : foo s xs
foo :: a -> [a] -> [a] foo s (x:xs) = s : x : foo s xs foo _ [] = []
is a little faster than the SATed isgo (about 4-5% in the benchmark). Compiled with optimisations, it makes no difference whether foo (of course we need a better name) is a top-level function or local to intersperse, but without optimisations, a top-level function is better. Also nice is that that gives identical core for all optimisation levels (0,1,2) [apart from the strictness/unfolding information, which is absent with -O0]. (Tested with 6.12.3 and HEAD.)
So far, the above is IMO the best implementation. A good name for foo remains to be found.
prependToAll
I don't like 'prepend' because prepend suggests only putting something before a list (with the given type, it should be (:)) and not changing anything inside.
If it's not to be exported from Data.List (and I don't consider it useful enough to be), maybe intersperseLoop wouldn't be too daft.
I consider it useful, because the "natural" implementation: prependToAll s = foldr (\ x r -> s : x : r) [] seems to leak without optimization. Cheers Christian
Cheers, Daniel