Am Freitag 30 Oktober 2009 14:32:35 schrieb Matthias Guedemann:
Hi Daniel,
That gives
combinations n xs = foldr f [[]] (replicate n xs)
pointfree, for extra goodness:
-- pointfree f inline combinations n xs = foldr ((. (. (:)) . flip map) . (>>=)) [[]] (replicate n xs) -- eliminate xs combinations n = foldr ((. (. (:)) . flip map) . (>>=)) [[]] . replicate n -- completely pointfree combinations = (foldr ((. (. (:)) . flip map) . (>>=)) [[]] .) . replicate
thank you, looks rather strange to me but works well.
Yes :D The pointfree f is nicely obfuscated. But if your friend is a perl coder, he should be able to appreciate that. The standard way to express f, however, is liftM2 (:), so combinations = (foldr (liftM2 (:)) [[]] .) . replicate -- isn't that boring? But earnestly, replicateM is the thing to use.
regards