Re: [boost] proto "boolean" laws (was Re: proto::tag naming convention

From: Eric Niebler (eric_at_[hidden])
Date: 2007-04-29 13:26:18

Larry Evans wrote:
> On 04/27/2007 03:25 PM, Eric Niebler wrote:
>> Larry Evans wrote:
>>
>>> why not
>>> do the following renames:
>>>
>>>   proto::_       -> proto::true_
>>>
>>>   proto::not_<_> -> proto::false_
>>>
>>> ?
>>
>> No, proto::_ is a placeholder. And proto::not_<> can logically negate 
>> any grammar, not just proto::_.
>>
> Actaully, the following is what I had in mind:
> 
> namespace boost
> {
> namespace proto
> {
>        struct
>      true_
>      : _
>      {};
>        struct
>      false_
>      : not_<true_>
>      {};
> 
> }}//exit boost::proto namespace
> 
> Why?  Because I think (I haven't tested it) the same
> laws for mpl::bool_ and it's associated operations:
> 
>    mpl::not_
>    mpl::and_
>    mpl::or_
> 
> would apply to proto's true_, false_, not_,....

I guess I don't see how these types would be used. In what contexts 
would using proto::true_ make more sense than using proto::_ ?

-- 
Eric Niebler
Boost Consulting
www.boost-consulting.com