Hi, Am Donnerstag, den 01.12.2011, 11:28 +0100 schrieb Joachim Breitner:
Now I’d like to implement streaks in terms of build and foldr such that it is subject to list fusion.
one half of the task is quite doable: streaks' :: [Integer] -> [[Integer]] streaks' xs = foldr streaksF [] xs streaksF :: Integer -> [[Integer]] -> [[Integer]] streaksF i [] = [[i]] streaksF i ([x]:ys) = [i,x]:ys streaksF i ((x1:x2:xs):ys) = if i `compare` x1 == x1 `compare` x2 then (i:x1:x2:xs):ys else [i]:(x1:x2:xs):ys so I can make streaks a somewhat well-behaving consumer. The task to create the lists using build remains. (The function only works correctly on lists where no two adjacent elements are the same, and it behaves differently than the code in the first mail on [2,1,2]; it builds [[2],[1,2]] instead of [[2,1],2]. That is ok for my purposes.) Greetings, Joachim -- Joachim "nomeata" Breitner mail@joachim-breitner.de | nomeata@debian.org | GPG: 0x4743206C xmpp: nomeata@joachim-breitner.de | http://www.joachim-breitner.de/