Re: [Boost-users] [Proto] How to access the grammar of an expression?

Subject: Re: [Boost-users] [Proto] How to access the grammar of an expression?
From: Thomas Heller (thom.heller_at_[hidden])
Date: 2010-09-24 10:52:45

Roland Bock wrote:

> On 09/24/2010 02:33 PM, Roland Bock wrote:
>> Hi,
>>
>> ist there a way to access the grammar that was used to construct an
>> expression?
>>
>> I have defined a metafunction
>>
>> template<class Left, class Right>
>> struct grammar_less: mpl::false_ {};
>>
>> which has specialization for some grammar combinations.
>>
>> Now I want to define a function that can take two arguments so that
>>
>> child0.grammar < child1.grammar
>>
>>
>> Any idea how to do that? My test-code is attached.
>>
>>
>> Regards,
>>
>> Roland
>>    
> Hi,
> 
> since I know the structure of the types in question, I can circumvent
> the problem as shown in the attached code. Not nice, but I could
> probably use it.
> 
> Regards,
> 
> Roland

you can compute that type information directly in your proto transform:

struct sorted_argument_function:
    proto::and_
    <
       proto::function<fun_terminal, proto::_, proto::_>,
       proto::if_
       < 
          grammar_less<
             proto::_value(proto::_child0(proto::_child1))
           , proto::_value(proto::_child0(proto::_child2))>()
       >
    >
 {};

btw: there is a proto specific list: proto_at_[hidden]