On Fri, Dec 4, 2009 at 6:42 AM, Christian Maeder
Daniel Fischer schrieb:
Am Mittwoch 02 Dezember 2009 18:54:51 schrieb Christian Maeder:
Daniel Fischer schrieb:
However, according to a couple of tests, the "funkyName" version is somewhat faster and allocates less. My timing tests showed that your fpairs version is fastest.
Interesting. Using a faster version of "sequence":
http://www.haskell.org/pipermail/haskell-cafe/2009-November/069491.html
\begin{code} allPossibilities :: [[a]] -> [[a]] allPossibilities [] = [[]] allPossibilities (l:ls) = [ x : xs | x <- l, xs <- allPossibilities ls]
I am confused. This is exactly sequence. How is this a faster version? Other than maybe avoiding some dictionary-passing? Incidentally there is a "better" version of sequence for finding products of lists: allPossibilities :: [[a]] -> [[a]] allPossibilities [] = [[]] allPossibilities (l:ls) = [ x : xs | xs <- allPossibilites ls, x <- l ] Or, the general form (I don't know of a use other than for lists, however): sequence' :: Applicative f => [f a] -> f [a] sequence' [] = pure [] sequence' (x:xs) = liftA2 (flip (:)) xs x The difference is that it binds the tail of the list first, so the generated tails are shared. This means less consing, less GC strain, and a lot less memory usage if you store them. Mind, the answers come out in a different order. Luke