Re: [boost] why or_, and_ names? (was Re: Preliminary submission: Boost.Proto DSEL Framework

From: Eric Niebler (eric_at_[hidden])
Date: 2007-04-04 14:14:10

Larry Evans wrote:
> On 04/04/2007 02:18 AM, Eric Niebler wrote:
> 
>> As discussed here recently, Boost.Proto is an expression template (ET) 
>> framework for building domain-specific embedded languages (DSEL). The 
>> purpose of this preliminary submission is to solicit feedback prior to a 
>> full submission (and to buy myself a little time to polish the 
>> docs/tests/examples :-).
>>
> Proto uses or_ and and_ for alternatives
> and sequences. It seems that alt_ and seq_ would be closer
> to the spirit names.   Any reason why those names were
> preferred over alt_ and seq_?

Because for what they do, or_ and and_ are the right names. :-) You 
realize that these do not create expression templates, right? They are 
part of proto's meta-grammar facility. If you want to know if an 
expression type E matches grammar G1 or G2, you use:

   proto::matches<E, proto::or_<G1, G2> >

That's a compile-time boolean test. Proto::and_ behaves similarly. Like 
mpl::or_ and mpl::and_ (and like || and &&) these do short-circuit 
evaluation.

HTH,

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