[boost] Interest in a list comprehension library?

Subject: [boost] Interest in a list comprehension library?
From: Brent Spillner (spillner_at_[hidden])
Date: 2010-12-19 13:40:42

I uploaded sample code to the Vault (in the "Miscellaneous/"
directory) that provides a concise notation for list comprehensions.
The comprehensions are evaluated lazily and can be used to populate a
std::list, vector, or deque, appended to the same, inserted after a
given iterator, or interpreted as a boost::range, including
compatibility with BOOST_FOREACH.  Containers, iterator-defined
ranges, or nullary function objects can be used as generators, and
arbitrary function objects can be used to specify filter conditions.

For example, the Pythagorean Triples example from
http://rosettacode.org/wiki/List_comprehensions can be coded as

std::vector< boost::tuple<int,int,int> > triples =_(x, y, z)[x <<=
range(1, n), y <<= range(x, n), z <<= range(y, n), x*x + y*y == z*z];

, and the (toy) prime number generator at
http://www.secnetix.de/olli/Python/list_comprehensions.hawk can be
implemented as

  std::vector<int> nonprimes = _(j)[i <<= range(2, sqrt_max), j <<=
range(2 * i, sqrt_max * sqrt_max, i)];

  boost::function<std::vector<int>::const_iterator ()> is_composite
       = bind(std::find<std::vector<int>::const_iterator, int>,
nonprimes.begin(), nonprimes.end(), ref(p));

  BOOST_FOREACH(int x, (_(p)[p <<= range(2, sqrt_max * sqrt_max),
call(is_composite) == nonprimes.end()])) { std::cout << x <<
std::endl; }

(Note the use of call() to represent delayed invocation, and the extra
() around the comprehension when used with BOOST_FOREACH.)

I've tested this so far with GCC 4.4.4, GCC 4.5.2, and Clang 2.9,
using Boost 1.42 and 1.45, and with and without -std=c++0x.  Reports
of success/failure with other environments are most welcome.  The code
is still in a prototype stage, so I'm more than happy to take design
suggestions and would love to hear about use cases I've overlooked.
If there's sufficient interest I will work on getting it to production
quality and writing some real documentation.  I apologize in advance
for wasting everybody's time if something like this already exists in
Phoenix; I'm not too familiar with it but I skimmed the docs and
didn't see anything.

Enjoy,
Brent