Proto for Boost mailing list page: Re: [proto] looking for an advise

Subject: Re: [proto] looking for an advise
From: Joel Falcou (joel.falcou_at_[hidden])
Date: 2010-12-27 05:26:46

On 27/12/10 11:02, Maxim Yanchenko wrote:
> Hi Eric and other gurus,
>
> Sorry in advance for a long post.
>
> I'm making a mini-language for message processing in our system.
> It's currently implemented in terms of overloaded functions with
> enable_if<match<Grammar>>  dispatching, but now I see that
>    
Dont. this increases copiel time and provide unclear error. Accept 
anykind of expression adn use matches in a
static_assert with a clear error ID.

> (a) I'm reimplementing Phoenix which is not on Proto yet in Boost 1.45.0 (that's
> how I found this mailing list). It would be great to reuse what Phoenix has;
>    
Isn't it in trunk already Thomas ?
> (b) I need to do several things on expressions and I don't know what would be
> the best way to approach them all.
>
> Here is a background.
> Every message is a multiset of named fields (i.e. is a multimap
> FieldName->FieldValue).
> I have a distinct type for each FieldName, so I can do some multiprogramming on
> sets of FieldNames, like making generating a structure that will hold values of
> the fields I need, by list of field names (e.g. fusion::map).
>
> While processing a message, I can do some checks like if particular field is
> present, if it's equal or not to some value, if it matches a predicate etc.
> They are implemented as a set of predicate functions "condition" like
>
>    template<  class Msg, class Expr>
>    typename boost::enable_if<  proto::matches<Expr, proto::equal_to<  proto::_,
> proto::_>  >, bool>::type
>    condition( const Msg&  msg, const Expr&  expr )
>
> with various condition grammars in enable_if<matches<...>>
>
>    
Again, use matches inside the function body.
> (a) everything runs on enable_if. I expect it to become more concise and clean
> if I use either transforms or contexts.
>    
You need none. Put your grammar into a domain with a proper context and 
proto will check operators overload for you.
> (b) a lot of Phoenix is basically reimplemented from scratch (thanks Eric, with
> Proto it was very easy to do!). But I don't know how to extend Phoenix so it
> could work in my expressions with my things like "any_field", "optional",
> "mandatory" etc.
>    
Better see what Thomas has up his sleeves in Phoenix.