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

From: Larry Evans (cppljevans_at_[hidden])
Date: 2008-03-20 20:04:23

On 03/20/08 18:10, Eric Niebler wrote:
> 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.
> 
So:

   expr<tag::shift_right, Args, 20>

is a valid expression?