As discussed here recently, Boost.Proto is an expression template (ET) framework for building domain-specific embedded languages (DSEL). The purpose of this preliminary submission is to solicit feedback prior to a full submission (and to buy myself a little time to polish the docs/tests/examples :-). << Marketing Blurb >> Boost.Proto eases the development of domain-specific embedded languages (DSELs). Use Proto to define the primitives of your mini-language and let Proto handle the operator overloading and the construction of the expression parse tree. Immediately evaluate the expression tree by passing it a function object. Or transform the expression tree by defining the meta-grammar of your mini-language, decorated with an assortment of tree transforms provided by Proto or defined by you. Then use the meta-grammar to give your users short and readable syntax errors for invalid expressions! An expression template library developed with Proto is declarative and readable. In short, Proto is a DSEL for defining DSELs. << Hello, World >> Here's the required hello world example in proto. It builds an expression template and evaluates it. (The docs have more interesting examples.) #include <iostream> #include <boost/xpressive/proto/proto.hpp> #include <boost/xpressive/proto/context.hpp> #include <boost/typeof/std/ostream.hpp> using namespace boost; proto::terminal< std::ostream & >::type cout_ = { std::cout }; template< typename Expr > void evaluate( Expr const & expr ) { proto::default_context ctx; proto::eval(expr, ctx); } int main() { evaluate( cout_ << "hello" << ',' << " world" ); return 0; } << Documentation (such as it is) >> http://boost-sandbox.sourceforge.net/libs/proto/doc/html/index.html << Download >> proto.zip at http://boost-consulting.com/vault/index.php?&directory=Template%20Metaprogramming << Requirements >> Tested with Boost RC 1.34 and HEAD. Feedback is most welcome. -- Eric Niebler Boost Consulting www.boost-consulting.com