Re: [Haskell-cafe] file splitter with enumerator package

I just found another solution that seems to work, although I don't fully understand why. In my original function where I used EB.take to strictly read in a Lazy ByteString and then L.hPut to write it out to a handle, I now use this instead (full code in the annotation here: http://hpaste.org/49366): EB.isolate bytes =$ EB.iterHandle handle It now runs at the same speed but in constant memory, which is exactly what I was looking for. Is it recommended to nest iteratees within iteratees like this? I'm surprised that it worked, but I can't see a cleaner way to do it because of the other parts of the program that complicate matters. At this point I've achieved my original goals, unusual as they are, but since this has been an interesting learning experience I don't want it to stop there if there are more idiomatic ways to write code with the enumerator package. On Mon, Jul 25, 2011 at 4:06 AM, David McBride wrote:

Well I was going to say:

import Data.Text.IO as T import Data.Enumerator.List as EL import Data.Enumerator.Text as ET

run_ $ (ET.enumHandle fp $= ET.lines) $$ EL.mapM_ T.putStrLn

for example.  But it turns out this actually concatenates the lines together and prints one single string at the end.  The reason is because it turns out that ET.enumHandle already gets lines one by one without you asking and it doesn't add newlines to the end, so ET.lines looks at each chunk and never sees any newlines so it returns the entire thing concatenated together figuring that was an entire line. I'm kind of surprised that enumHandle fetches linewise rather than to let you handle it.

But if you were to make your own enumHandle that wasn't linewise that would work.

On Mon, Jul 25, 2011 at 6:26 AM, Yves Parès wrote:

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Okay, so there, the chunks (xs) will be lines of Text, and not just random blocks. Isn't there a primitive like printChunks in the enumerator library, or are we forced to handle Chunks and EOF by hand?

2011/7/25 David McBride

...

blah = do  fp <- openFile "file" ReadMode  run_ $ (ET.enumHandle fp $= ET.lines) $$ printChunks True

printChunks is super duper simple:

printChunks printEmpty = continue loop where        loop (Chunks xs) = do                let hide = null xs && not printEmpty                CM.unless hide (liftIO (print xs))                continue loop

       loop EOF = do                liftIO (putStrLn "EOF")                yield () EOF

Just replace print with whatever IO action you wanted to perform.

On Mon, Jul 25, 2011 at 4:31 AM, Yves Parès wrote:

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Sorry, I'm only beginning to understand iteratees, but then how do you access each line of text output by the enumeratee "lines" within an iteratee?

2011/7/24 Felipe Almeida Lessa

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On Sun, Jul 24, 2011 at 12:28 PM, Yves Parès wrote:

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If you used Data.Enumerator.Text, you would maybe benefit the "lines" function:

lines :: Monad m => Enumeratee Text Text m b

It gets arbitrary blocks of text and outputs lines of text.

...

But there is something I don't get with that signature: why isn't it: lines :: Monad m => Enumeratee Text [Text] m b ??

Lists of lines of text?

Cheers, =)

-- Felipe.

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