Re: [boost] [proto] design of expr<>

Larry Evans wrote:

I don't think it solves any problem that can't already be solved, but it makes the solution clearer. It's clearer because the arity is associated with the tag *not* the expression. The arity of a tag does not depend on the expression; so, it should not be in the expression. Instead the arity of the tag determines the expression validity.

Sorry, but that's backwards. Tags don't have arities, expressions do. The arity of tag::function could be anything. The arity represents the number of children of an expression node. So the arity is a very real part of an expression. -- Eric Niebler Boost Consulting www.boost-consulting.com