[Haskell-cafe] file splitter with enumerator package

[Eric Rasmussen]

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 <dmcbride at neondsl.com> 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) $$ EL.mapM_ T.putStrLn
>
> for example.  But it turns out this actually concatenates the lines
> together and prints one single string at the end.  The reason is
> because it turns out that ET.enumHandle already gets lines one by one
> without you asking and it doesn't add newlines to the end, so ET.lines
> looks at each chunk and never sees any newlines so it returns the
> entire thing concatenated together figuring that was an entire line.
> I'm kind of surprised that enumHandle fetches linewise rather than to
> let you handle it.
>
> But if you were to make your own enumHandle that wasn't linewise that
> would work.
>
> On Mon, Jul 25, 2011 at 6:26 AM, Yves Parès <limestrael at gmail.com> wrote:
>> Okay, so there, the chunks (xs) will be lines of Text, and not just random
>> blocks.
>> Isn't there a primitive like printChunks in the enumerator library, or are
>> we forced to handle Chunks and EOF by hand?
>>
>> 2011/7/25 David McBride <dmcbride at neondsl.com>
>>>
>>> blah = do
>>>  fp <- openFile "file" ReadMode
>>>  run_ $ (ET.enumHandle fp $= ET.lines) $$ 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 <limestrael at gmail.com> wrote:
>>> > 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 <felipe.lessa at gmail.com>
>>> >>
>>> >> On Sun, Jul 24, 2011 at 12:28 PM, Yves Parès <limestrael at gmail.com>
>>> >> wrote:
>>> >> > 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.
>>> >
>>> >
>>> > _______________________________________________
>>> > Haskell-Cafe mailing list
>>> > Haskell-Cafe at haskell.org
>>> > http://www.haskell.org/mailman/listinfo/haskell-cafe
>>> >
>>> >
>>
>>
>
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