Lazy evaluation can sometimes be helpful here. I once wrote a
raytracer that computed the resulting image using a pure function that
returned a list of the RGB colors of the pixels: [(Word8, Word8,
Word8)]
When plotting the pixels to the screen in the IO monad, the value of
each pixel would be computed on demand, and so the image was shown
progressively as the calculations were performed.
I was new to haskell when I made this program and when I ran the
program for this first time I was expecting to experience a long pause
and then a display of the final image. I was very surprised to see
progressive rendering!
On Nov 29, 2007 12:03 AM, Andrew Coppin
In a "normal" programming language, you might write something like this:
for x = 1 to 1000000 print x ...do slow complex stuff... next x
In Haskell, you're more likely to write something like
result k = filter my_weird_condition $ map strange_conversion $ unfoldr ...
That means that when you try to process the result, lots of processing happens, and your program just appears to lock up until a result is produced. So, like, how do you make it so that some kind of progress information is output while it's working? (Aside from dunking everything into the IO monad and ruining all your beautiful abstractions.) There doesn't seem to be a clean solution to this one...
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe