Proto for Boost mailing list page: Re: [proto] Externalizing grammar pattern matching

Subject: Re: [proto] Externalizing grammar pattern matching
From: joel falcou (joel.falcou_at_[hidden])
Date: 2010-11-23 14:18:16

On 23/11/10 17:20, Eric Niebler wrote:
> On 11/23/2010 10:19 AM, Joel Falcou wrote:
>> So, question is: is there a way to have an extensible list of
>> when<pattern,rule>  that can be extended "from the outside", something
>> like a proto::switch_ but with patterns instead of tag ?
> No. The best you can do is document how to define a new Proto algorithm
> from an old one:
>
>    struct Old : proto::or_<  ...>  {};
>
>    struct New : proto::or_<  my_stuff, Old>  {};
>
> Now everywhere in your library that you have the Old algorithm
> hard-coded, you need to make it a template parameter so that your stuff
> can be used with an extended algorithm.
Can't the new extrnal_transform be of any help ?