boost-proto

I was playing with Boost.Proto, mostly for fun and to see if in future I could make some use of it in my own projects. That said, as probably most beginners of this library, i've played with a modified version of the 'lazy vector' example, but using transforms instead of contexts to perform the evaluation. The vector is defined as follows (ok, i know, 'vector' is not a good name for something defined at the global namespace scope...) template <std::size_t D, class T> class vector { T data_[D]; enum { dimension = D }; // Constructors, destructors... }; // expression wrapper template <class>

In the Boost Phoenix article, "Transforming the Expression Tree", here , a set of specialisations of a custom invert_actions class, are used to invert binary arithmetic expressions. For example a+b becomes a-b ; a*b becomes a/b ; and vice versa for both. This involves a recursive traversal of the expression tree - however, this traversal stops when an expression involving an operator not explicitly handled is encountered. For example, _1+_2-_3 will become _1-_2+_3 , but _1+_1&_2 will stay as it is (there is no handler for & ). let(_a = 1, _b = 2) [ _a+_b ] will also be left unchanged. I had

( EDITED both title and main text and created a spin-off question that arose) For our application it would be ideal to parse a simple DSL of logical expressions. However the way I'd like to do this is to parse (at runtime) the input text which gives the expressions into some lazily evaluated structure (an expression template) which can then be later used within more performance sensitive code. Ideally the evaluation is as fast as possible using this technique as it will be used a large number of times with different values substituting into the placeholders each time. I'm not expecting the

Background question: boost.proto + detect invalid terminal before building the expression tree . Hi, what i'm trying to achieve is create a copy of an expression tree, where all vectors are substituted with their begin iterators (in my case is a raw pointer) increment the iterators in place dereference iterators in the tree, but that part should be relatively easy. So, for 1. I ended up with this code /////////////////////////////////////////////////////////////////////////////// // A transform that converts all vectors nodes in a tree to iterator nodes struct vector_begin : proto::transform