[Haskell-cafe] Progress indications
thomas.hartman at db.com
Thu Nov 29 10:43:29 EST 2007
Obviously heaps better than what I initially proposed.
However, I would argue to go boldly with unsafePerformIO, which is the
same thing Debug.Trace uses
since we are after debug.trace -like behavior.
In particular, you wouldn't be able to use the unsafeInterleaveIO version
to do a progress indicator for the function I initially proposed
> t = foldr (+) 0 [1..10000]
since your lift would wind up being lifted into IO. But you would be able
to use the unsafePerformIO version, just like in what I initially proposed
you could use trace.
t = foldr (+) 0 ( lessSafeMonitoryProgress f [1..10000] )
where f i | i mod 1000 == 0 = (putStrLn . show ) i
| otherwise = return ()
David Roundy <droundy at darcs.net>
Sent by: haskell-cafe-bounces at haskell.org
11/28/2007 06:16 PM
haskell-cafe at haskell.org
Re: [Haskell-cafe] Progress indications
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.
Department of Physics
Oregon State University
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