Re: [Boost-users] [Xpressive] Nested patterns and sub-matches' semantic values

Subject: Re: [Boost-users] [Xpressive] Nested patterns and sub-matches' semantic values
From: Eric Niebler (eniebler_at_[hidden])
Date: 2013-05-30 15:47:11

On 13-05-30 08:35 AM, Simon wrote:
> Hi,
>   For one part of a large project, I need to parse math and turn the
> "mathematical objects" into a C++ abstraction of them.  Is it possible
> that a nested pattern hold semantic values within itself and can be
> queried for that value somehow?  As if a match were a function of its
> sub-patterns' matches, if that makes sense...
> 
> Code might speak better than my english:
> 
>   class math_number {...};
>   class math_addition {...};
>   class math_arglist {...};
>   class math_funcdef {...};
> 
>   sregex integer = (s1= +_d)
>      [ return math_number( as<int>(s1) ) ];
> 
>   sregex addition = (s1= integer) >> '+' >> (s2= integer)
>      [ return math_addition( as<math_number>(s1), as<math_number>(s2) ) ];
> 
>   sregex arglist = (s1= identifier) >> *( ',' >> (s2= arglist))
>     [ std::vector<math_id> ids( as<math_arglist>(s2).begin(),
> as<math_arglist>(s2).end() );
>        ids.push_back(as<math_id>(s1));
>        return ids; ]
> 
>   sregex funcdef = ((s1= identifier) >> '(' >> (s2= arglist) >> ")=" >>
> (s3= addition))
>      [ return math_funcdef( as<math_id>(s1), as<math_arglist>(s2),
> as<math_addition>(s3) ) ];
> 
>   I just want to avoid the funcdef above to be responsible for the
> construction of the various math_* objects the funcdef will hold (some
> of which will be complex to construct).  And if I really must store the
> objects in an external stack, how should the parent-objects find their
> child-objects?

It really sounds to me that this problem would be better addressed by
Boost.Spirit and its attributed parsers.

-- 
Eric Niebler
Boost.org