[Haskell-cafe] file splitter with enumerator package

[David McBride]

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.
>> >
>> >
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>
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