On 11/17/06, Henning Thielemann <[EMAIL PROTECTED]> wrote:
On Fri, 17 Nov 2006, Clara Zamolo wrote: > buildCouples = snd . foldl op (0,[]) > where > op (v,xs) x = (v+x,xs++[(x,v)]) >
You could make something like this that doesn't have quadratic-type appends by accumulating functions instead of lists: Prelude> snd (foldl (\(s,f) x -> (x+s,f . ((x,s):))) (0,id) [1..6]) [] [(1,0),(2,1),(3,3),(4,6),(5,10),(6,15)] but this is better:
I suggest using 'scanl' and then 'zip' the result together with the original list.
Or, equivalently, use mapAccumL from the Data.List library: Prelude Data.List> snd $ mapAccumL (\s x -> (s + x,(x,s))) 0 [1..6] [(1,0),(2,1),(3,3),(4,6),(5,10),(6,15)] /g _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
