[Haskell-cafe] transparent parallelization

Dave Tapley dukedave at gmail.com
Tue Sep 18 16:48:26 EDT 2007

If I recall correctly a rather neat way of exploiting this property of
qsort is exploited with Nested Data Parallelism and covered in this

Good food for thought :)


On 18/09/2007, Thomas Girod <girodt at gmail.com> wrote:
> Hi there. Beeing rather new to the realm of Haskell and functional
> programming, I've been reading about "how is easier it is to parallelize
> code in a purely functional language" (am I right saying that ?).
> My knowledge of parallelization is also very weak, but I've been thinking
> about this and I have a question. Let's say we take a small piece of code,
> like the quicksort algorithm.
> > qsort [] = []
> > qsort (x:xs) = qsort lesser ++ [x] ++ qsort greater
> >         where lesser = filter (<x) xs
>                        greater = filter (>=x) xs
> (actually I didn't test this code, this is just for the example)
> Here, computing "lesser" and "greater" are two disjoint actions - we don't
> need the result from one to compute the other, and haskell does not allow
> one to alter data so that would change the behaviour of the other. So I
> guess those could be run in parallel.
> Would it be fairly simple to automatically determine parts of code that can
> be run in parallel, and parts that cannot (at least in non-monadic code) ?
> So the final question is : if it is possible to automatically define
> segments of code that can be run in parallel, is [insert compiler name here]
> compiling this code as a one thread thing, or as a multithreaded version ?
> I guess on single processor machines, it is more efficient to do it as a
> single thread - but with those "many-cores" processors that are coming, it
> probably won't be true anymore.
> Sorry if this post is blowing off open doors (I guess this doesn't mean
> anything in english but it sounds cool) ...
> Regards
> Thomas Girod
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