On Jul 27, 2015, at 6:07 PM, David Powell <david.pow...@monash.edu> wrote: > > As Bob pointed out the problem is reopening your files.
I definitely did not see how I was reopening the files! > Something like this should fix it: > fileHandles <- Map.fromList `fmap` mapM (\x -> do h <- openFile ("out/" ++ > x) WriteMode > return (x,h)) allMers That was exactly what I wanted, but I swear I never would have hit upon using "fmap" to get it. Here's what I finally got: https://github.com/kyclark/kmer-binner/blob/master/haskell/Binner.hs I finally have some Haskell that outperforms my Perl! Thanks so much for all the input! I could not have done it without your help. I gladly welcome any further suggestions. Ken