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May 2004

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342 discussions

RE: [boost] Generative programming support in boost
by Reece Dunn 01 May '04

01 May '04

Dave Gomboc wrote: >I'm revisiting Czarnecki and Eisenecker's work (Generative Programming: >Methods, Tools, and Applications) from 2000. I'm wondering what is >available in boost that exploits (or even advances) on the techniques >and code examples given there. >It occurs to me that both the concept_check and the mpl library have >something to offer in this respect. At the very least, there are few >obvious things (e.g. if, apply_if, etc. in mpl). Is anyone actively >applying boost code in this area? Have you had a look at Boost.Spirit and the related Phoenix/Fusion libraries? Spirit is a lexer/parser generator that allows you to write BNF grammars in C++ that are close to the actual BNF grammar declerations, as well as providing a set of grammar recognisers like real numbers. See the documentation for more information. Spirit allows you to bind actions to the grammar (e.g. summing the numbers read from a file/user input). There is closure support, alliowing a grammar rule to have data bound to it, and the Phoenix/Fusion library provides a mechanism for writing lazily evaluated C++-like code (e.g. if, while as well as STL actions such as push_back and assign). e.g. std::vector< float > v; ... rule<> = real_p[ push_back_p( v ) ] >> ',' >> real_p[ push_back_p( v ) ] NOTE: The Spirit documentation contains this example with a more detailed explanation. There is also the Lambda library - which is currently being rewritten to sit on top of the Fusion framework - that allows you to use Lambda expressions in C++ code, e.g.: std::for_each( c.begin(), c.end(), n += _1 ); // see Lambda docs for correct usage There has also been a review of the FC++ library (see the mail archives for details) that attempts to provide a functional language framework, and although it has not yet been accepted into Boost, there are some powerful concepts like Lazy Lists. It provides its own Lambda implementation and equivalent of Boost.Function/Boost,Bind. Even though this is functional programming (like Haskell) there is a heavy reliance on template metaprogramming as well as adding to the existing generative framework. If you want to find out how extensively the MPL library is used in Boost, do a search for "mpl::". I know that the Serialisation library is using it. Also, there are several workarounds for the current lack of typeof/auto in various libraries that need it. My I/O formatters library (boost-sandbox/outfmt) uses a technique similar to this to map a type to a classification (e.g. container, array, n-ary) in order to build the appropriate formatter so that it can be correctly written to/read from a C++ stream. The documentation is currently out of synch with the implementation and examples, but I am revising it at the moment. Also, the STL provides generative support with iterators/iterator_traits, algorithms and functors. The Boost library has enhanced these with the Iterator Adaptors library, a better iterator_traits and other stuff. Hope that helped. Regards, Reece _________________________________________________________________ Express yourself with cool emoticons - download MSN Messenger today! http://www.msn.co.uk/messenger

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BOOST_TRY, can we make it into CVS?
by Pavel Vozenilek 01 May '04

01 May '04

I would like to ask someone with write access to CVS to create file boost/details/exception_helpers.hpp (or so) with content: #include <boost/config.hpp> #include <boost/detail/workaround.hpp> #if !(defined BOOST_NO_EXCEPTIONS) # define BOOST_TRY { try # define BOOST_CATCH(x) catch(x) # define BOOST_RETHROW throw; # define BOOST_CATCH_END } #else # if BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564)) # define BOOST_TRY { if ("") # define BOOST_CATCH(x) else if (!"") # else # define BOOST_TRY { if (true) # define BOOST_CATCH else if (false) # endif # define BOOST_RETHROW # define BOOST_CATCH_END } #endif circular_buffer, serialization and multi_index_container may use this code. It was discussed on the list and reaction was rather positive. TIA /Pavel

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