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
http://darcs.haskell.org/ghc-6.6/packages/base/Debug/Trace.hs
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 ()
Make sense?
thomas.
David Roundy <[EMAIL PROTECTED]>
Sent by: [EMAIL PROTECTED]
11/28/2007 06:16 PM
To
haskell-cafe@haskell.org
cc
Subject
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.
--
David Roundy
Department of Physics
Oregon State University
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