On 6/5/2010 2:26 PM, joel falcou wrote:

after digetsing all the contents of eric boost'con talk i came to the conclusion that epxression-tempalte enabled statement may be part of proto like operators. One can see the ability of having if or for as a real expression geenrator for any EDSL as actaully a feature.

What may prevent if_, for_ and such to be first class, EDSL agnostic citizen fo proto ?

Right now, Proto restricts itself to expressions. Proto isn't in the business of simulating C++ statements. That, to me, lies within the domain of C++-like DSELs -- BLL and Phoenix, for example. That's not to say something like this wouldn't generally be useful, but it's hard to know when to stop. DSEL-agnostic STL constructs? Map/reduce constructs? Concurrency constructs? I prefer to leave these to other libraries implemented on top of Proto. Besides, slurping that stuff into Proto raises hairy issues: what's the best syntax? And what's the best tree structure? As you know, Joel and I are of two minds about what a the AST for if/else should look like. Expressions are simple: don't mess with C++'s rules for precedence and associativity. Statements are a matter of taste. Once Phoenix 3 is implemented, you can easily reuse Phoenix 3 C++ statement-like expressions by making your domain a sub-domain of Phoenix's. -- Eric Niebler BoostPro Computing http://www.boostpro.com