Hello Cafe, First I'd like to thank Michael Snoyman and Gabriel Gonzalez for the work they've done on the conduit and pipes stream processing libraries, and all the accompanying tutorial content. I've been having fun converting a text processing app from C to Haskell. I'm seeing unexpectedly high memory usage in a stream-processing program that uses the conduit library. I've created a example that demonstrates the problem. The program accepts gzip files as arguments, and for each one, classifies each line as either Even or Odd depending on the length, then outputs some result depending on the Sink used. For each gzip file: action :: GzipFilePath -> IO () action (GzipFilePath filePath) = do result <- runResourceT $ CB.sourceFile filePath $$ Zlib.ungzip =$ CB.lines =$ token =$ sink2 putStrLn $ show result The problem is the following Sink, which counts how many even/odd Tokens are seen: type SinkState = (Integer, Integer) sink2 :: (Monad m) => SinkState -> Sink Token m SinkState sink2 state@(!evenCount, !oddCount) = do maybeToken <- await case maybeToken of Nothing -> return state (Just Even) -> sink2 (evenCount + 1, oddCount ) (Just Odd ) -> sink2 (evenCount , oddCount + 1) When I give this program a few gzip files, it uses hundreds of megabytes of resident memory. When I give the same files as input, but use the following simple Sink, it only uses about 8Mb of resident memory: sink1 :: MonadIO m => Sink Token m () sink1 = awaitForever (liftIO . putStrLn . show) At first I thought that sink2 performed so poorly because the addition thunks were being placed onto the heap until the end, so I added some bang patterns to make it strict. That didn't help however. I've done profiling, but I'm unable to figure out exactly what is being added to the heap in sink2 but not sink1, or what is being garbage collected in sink1, but not sink2. The full source is here: https://bitbucket.org/bryanvick/conduit-mem/src/HEAD/hsrc/bin/mem.hs Or you can clone the repo, which contains a cabal file for easy building: git clone git@bitbucket.org:bryanvick/conduit-mem.git cd comduit-mem cabal sandbox init cabal install --only-dependencies cabal build mem ./dist/build/mem/mem [GIVE SOME GZIP FILES HERE] You can change which sink is used in the 'action' function to see the different memory usage.