QSort in D: is this best?

[dsimcha]

== Quote from Philippe Sigaud (philippe.sigaud at gmail.com)'s article
> --0016e6db29968796e0047b5716c2
> Content-Type: text/plain; charset=ISO-8859-1
> On Mon, Dec 21, 2009 at 23:44, Andrei Alexandrescu <
> SeeWebsiteForEmail at erdani.org> wrote:
> > This is a great example that I don't have the time to look into now. In
> > essence the task is to generate all numbers of the form 2^^a*3^^b*5^^c where
> > a, b, and c are natural numbers.
> >
> > Currently Phobos doesn't have the means to compute the cross-product of
> > ranges. I encourage people to think about implementing that.
> >
> > Andrei
> I posted yesterday on D.announce that I have some code related to that:
> http://www.dsource.org/projects/dranges
> If some people are interested, I'd be delighted to have some feedback. The
> docs for the algorithm module is here:
> http://svn.dsource.org/projects/dranges/trunk/docs/algorithm2.html
> There is a cross-product for ranges (returning tuples), called combinations.
> As in,
> auto c = combinations(r1, r2, r3, r4); // Takes a variadic number of ranges.
> I put a Hamming numbers example in the docs, for the merge function.
> >From the docs :
> // Calculating Hamming numbers, numbers of the form 2^i * 3^j * 5^k
> // see http://en.wikipedia.org/wiki/Regular_number
> // Dijkstra's algorithm heavily uses merge.
> T[] hamming(T)(T[] r)
> {
>     return 1 ~ *merge2*(map!"2*a"(r),*merge2*(map!"3*a"(r),map!"5*a"(r)));
> }
> auto hammingNumbers =  iterate!hamming([1UL][]); // develops the
> Hamming sequence at each iteration.
> // 1,2,3,4,5,6,8,9,10,12,...
> // For the i-th iteration, the sequence is complete up to 2^i,
> // but has much more numbers already calculated.
> So I kind of cheat there: it's not Haskell's elegant self-recursive
> definition, but it's very near Dijkstra's algorithm and can be made a
> one-liner, if that's really a criteria... At each front call, iterate
> extends the sequence.
> merge2 is greedy and works only for two ranges (hence it's name), but I have
> a templated, predicate-aliased, lazy, n-ranges version called merge in the
> module.
>    Philippe


The work you've done looks excellent and will probably get noticed a lot more in a
few months when development of Phobos gets put back on the front burner.  I
apologize for the relative silence on what looks to be lots of very useful,
well-documented code, but the core D people are currently in a mad dash to tie up
all the loose ends of the core language ahead of Andrei's book.  Phobos and
libraries in general haven't been on the front burner since last spring.