[Haskell-cafe] Progress indications

[Nicolas Frisby]

This might be a little less invasive. You could add any unsafe* stuff
as you desire.

-- every hundred elements generates a trace marker
addTrace xs = addTrace' 100 0 where
   addTrace' 0 !cnt xs = Left cnt : addTrace' 100 cnt xs
   addTrace' n !cnt (x:xs) = Right x : addTrace' (n - 1) (cnt + 1) xs

separateTrace = partition isLeft



-- result k = filter my_weird_condition $ map strange_conversion $ unfoldr ...

observe k = do
  let (trace, result) = (filter my_weird_condition >< id) $
                              separateTrace . addTrace $
                              map strange_conversion $ unfoldr...
  print trace
  return result

On Nov 28, 2007 5:16 PM, David Roundy <droundy at darcs.net> wrote:
> On Wed, Nov 28, 2007 at 05:58:07PM -0500, Thomas Hartman wrote:
> > maybe Debug.Trace? like...
> >
> > import Debug.Trace
> >
> > t = foldr debugf 0 [1..10000]
> >
> > f :: Int -> Int -> Int
> > f = (+)
> >
> > -- same typesig as f
> > debugf :: Int -> Int -> Int
> > debugf x y | y `mod` 1000 == 0 = x + (trace (show y) y)
> > debugf x y = x + y
>
> Or, more flexibly:
>
> import System.IO.Unsafe ( unsafeInterleaveIO )
>
> monitorProgress :: (Int -> IO ()) -> [a] -> IO [a]
> monitorProgress f xs = mapM f' $ zip [0..] xs
>    where f' (n,x) = unsafeInterleaveIO (f n >> return x)
>
> You could, of course, make this a function
>
> lessSafeMonitoryProgress :: (Int -> IO ()) -> [a] -> [a]
>
> by using unsafePerformIO instead of unsafeInterleaveIO, but that seems
> slightly scary to me.
>
> In any case, you can stick this on whichever of the lists you want to
> monitor the progress of.
> --
> David Roundy
> Department of Physics
> Oregon State University
>
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