Bonjour Jean-Marc, "acc" contains the computation of the whole search up to a point. Calling it once (as part of the fold) makes it grow linearly in the size of the search space, but calling it twice (once more as "v <- acc") makes it grow exponentially. Cordialement, Li-yao On 01/23/2018 08:35 AM, Jean-Marc Alliot wrote:
I apologize if my question is stupid, but here is a simple Haskell program which never stops.
However, if I comment the line (which is apparently useless): v<-acc The program works like a charm...
I am using GHC 8.0.2 (debian sid) and multiset 0.3.3. If anyone has an idea, I would gladly hear it.
Thanks in advance
PS: don't try to understand what the program is doing; it is just the reduction to a few lines of a much larger code; I have tried to find a smaller subset which is not working "properly". PPS: The program can also be downloaded from: http://www.alliot.fr/tmp/example.hs
import qualified Data.IntMultiSet as IMS
b :: IMS.IntMultiSet b = IMS.fromList ([1, 2, 3, 4])
search :: IMS.IntMultiSet -> Int -> IO Bool search mynumbers nb = ins mynumbers (return False) where ins numbers acc = do v <- acc IMS.fold (\x acc1 -> let numbers2 = IMS.delete x numbers in IMS.fold (\y acc2 -> let numbers3 = IMS.delete y numbers2 res = x + y in if res == nb then (return True) else ins (IMS.insert res numbers3) acc2) acc1 numbers2) acc numbers
main = do v <- search b 999999999 print v _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.