Roman Leshchinskiy wrote:
On 16/05/2010, at 11:54, Mark Wassell wrote:
Hi,
This possibly might go against the spirit of what Stream programming is about
but I having difficulties converting an imperative algorithm [1] into Haskell
and think it would be easier if I was able to write it in a monadic style with
operations to read and write from and to the streams.
I first tried to approach it by delving into the innards of other Stream
functions to devise what I needed. I only got so far and the sticking point was
defining the Monad. I then approached it from the Monad side and although what
I have is workable, it probably isn't going to perform (for one it uses
fromStream and tailS on each read off the front of the stream).
Data.Array.Parallel.Stream serves only one purpose: to represent loops produced by
DPH in such a way that the compiler is able to optimise them well. Putting a monad
on top of that will very very likely break this. To be honest, I'm not sure why
you need the monad anyway. I would expect compression/decompression to be pure
functions of type Stream Word8 -> Stream Word8.
In any case, I would urgently recommend not to use Data.Array.Parallel.Stream
for anything at this point. This whole subsystem will soon die of old age and
be replaced by the much nicer stuff from package vector, specifically
Data.Vector.Fusion.Stream and Data.Vector.Fusion.Stream.Monadic. Note that the
latter implements monadic streams as described in
http://www.cse.unsw.edu.au/~rl/publications/recycling.html. Perhaps those can
be useful for you if you really need a monad.
Roman
Thanks. No, I don't need a Monad and I suspected it was a bad idea. It
was really needed for convenience as all I had to go on was a C
implementaiton of arithmetic coding (which included a getc part-way
through the code block which I hoped to map to something like a get from
the stream). However thanks to Stephen I have something better to work
from. I will also take a look at Data.Vector.Fusion.Stream.
Cheers
Mark
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