[Haskell-cafe] 'Progress bar' enumeratee

[David Hotham]

Thanks for the reply.

I did have a version along those lines at some point, but I felt it was 
cheating rather to print the dots not at the correct point in the stream.

Perhaps I've over-complicated for the sake of the learning experience, but I 
do like to have a version that passes on the correct number of bytes, then 
prints the ".", and then continues.

David

"Ertugrul Soeylemez" <es at ertes.de> wrote in message 
news:20110406163105.13cbc9a3 at angst.streitmacht.eu...
> "David Hotham" <david.hotham at blueyonder.co.uk> wrote:
>
>> I've spent some time over the last couple of days trying to write an
>> enumeratee that prints a "." every n bytes (with obvious intended use
>> as a progress tracker).  Seems like it oughtn't be hard, but it has
>> been a steep learning curve...
>>
>> I have come up with something that seems to do the job but I don't
>> know that I'm completely happy with it (or even that I completely
>> understand it, to be honest).
>>
>> If anyone more expert would be kind enough either to reassure me that
>> I'm doing it right or - more likely - to offer improvements /
>> suggestions on what obvious simplifications I have overlooked, I'd be
>> grateful.
>
> I think that using lazy bytestrings does not have any advantage here,
> since the enumerator creates the strict bytestrings at some point, then
> your enumeratee converts them into lazy ones just for counting.  Just
> use the straightforward approach:  Take the chunks and count the bytes
> like here:
>
>    {-# LANGUAGE ScopedTypeVariables #-}
>
>    dotsAt :: forall b m. MonadPeelIO m =>
>              Int -> Enumeratee ByteString ByteString m b
>    dotsAt n =
>        loop 0
>
>        where
>        loop :: Int -> Enumeratee ByteString ByteString m b
>        loop i' step@(Continue k) =
>            continue go
>
>            where
>            go :: Stream ByteString ->
>                  Iteratee ByteString m (Step ByteString m b)
>            go EOF = return step
>            go ch@(Chunks strs) = do
>                let (numDots, i) = divMod (i' + sum (L.map BC.length strs)) 
> n
>                tryIO $ BC.putStr (BC.replicate numDots '.')
>                k ch >>== loop i
>        loop i' step = return step
>
> I think, this is about the most straightforward and also the fastest
> approach.
>
>
> Greets,
> Ertugrul
>
>
> -- 
> nightmare = unsafePerformIO (getWrongWife >>= sex)
> http://ertes.de/