Re: [Boost-users] [proto] learning proto slowly, a small (math)complex library

Subject: Re: [Boost-users] [proto] learning proto slowly, a small (math)complex library
From: Eric Niebler (eric_at_[hidden])
Date: 2011-01-12 00:33:17

On 1/11/2011 2:58 AM, alfC wrote:
>> As Joel pointed out already, you need to wrap your expression templates to
>> give them their domain specific meaning. In your case, the cast operator.
>> This cast operator would need to have a context, or preferably a transform
>> (a transform is a grammar is a transform) to evaluate your expression to
>> std::complex<double>.
>> See:http://www.boost.org/doc/libs/1_45_0/doc/html/proto/users_guide.html#...
>> for an example with contexts.
>>
>> The steps to define a grammar that does the transformation are the
>> following:
>> 1) define a grammar that matches your expression
>>
> 
> ok, at the level I am working it seem that the following grammar is
> what I need. note that it is not recursive and it is a completely
> rigid structure.
> 
> struct complex_cartesian_grammar :
> 	proto::plus<
> 		proto::terminal<double>,
> 		proto::multiplies<
> 			proto::terminal<double>,
> 			proto::terminal<i_tag>
> 		>
> 	>{};
> (complete code at the end)

Like Joel says, it's just as simple to make this correct and general.
This is artifically constrained.

>> 2) attach semantic actions, step by step to your grammar rules
> 
> not so fast, how do I do that?

Read about transforms:

http://www.boost.org/doc/libs/1_45_0/doc/html/proto/users_guide.html#boost_proto.users_guide.back_end.expression_transformation

> I also defined the "domain"
> struct complex_cartesian_domain	:
> 	proto::domain<
> 		proto::generator< complex_cartesian_expr >,
> 		complex_cartesian_grammar
> 	>{};
> 
> I still have to somehow connect the define grammar with the expression
> itself. how?

Read about expression extension:

http://www.boost.org/doc/libs/1_45_0/doc/html/proto/users_guide.html#boost_proto.users_guide.front_end.adding_members_by_extending_expressions

> I also understand that the expression convertible to
> std::complex<double> must match double + double*i (the simple grammar)
> but again I don't understand how to do it.

See attached.

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com