[Haskell-cafe] 'Progress bar' enumeratee

[Ertugrul Soeylemez]

"David Hotham" <david.hotham at blueyonder.co.uk> wrote:

> 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.

Well, then just do the printing after calling the continuation:

    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
                    printDots = tryIO $ BC.putStr (BC.replicate numDots '.') >>
                                        hFlush stdout
                k ch >>== (\step -> printDots >> loop i step)
        loop i' step = return step

By the way, after trying out the code, I found that you should use
hFlush after printing.  Otherwise you may see the dots delayed.


Greets,
Ertugrul


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