more spirit madness - parser-types (rules vs int_parser<>) and meta-programming techniques

Question

The question is in bold at the bottom, the problem is also summarized by the distillation code fragment towards the end.

I am trying to unify my type system (the type sy

Answer 1

I'm not so sure I get the full extent of the question, but here are a few hints

• The line commented with // THIS is what I need to do. compiles fine with me (problem solved? I'm guessing you actually meant assigning a parser, not a rule?)

• Initialization of function-local static has been defined to be thread safe in the latest standard (C++11). Check your compiler support for C++0x threading. (If the initializer throws, a pass of the initialization statement will try to initialize again, by the way).

• rules alias()

  As described in http://boost-spirit.com/home/articles/doc-addendum/faq/#aliases

  You can create 'logical copies' of rules without having to actually value-copy the proto expression. As the FAQ says, this is mainly to allow lazy-binding

• The Nabialek Trick might be precisely what you need, basically it lazily selects a parser for subsequent parsing

  one = id;
  two = id >> ',' >> id;
  
  keyword.add
      ("one", &one)
      ("two", &two)
      ;
  
  start = *(keyword[_a = _1] >> lazy(*_a));
  

  In your context, I could see keyword defined as

  qi::symbols<char, qi::rule<Iterator>*> keyword;
  

  doing all the work with attributes from semantic actions. Alternatively,

  qi::symbols<char, qi::rule<Iterator, std::variant<std::string,int>() >*> keyword;
  

• Bring the rules under the same type (like shown in the previous line, basically)

  This is the part where I'm getting confused: You say you want to unify your type system. There might not be a need for strongtyped parsers (distinct attribute signatures).

  typedef boost::variant<std::string,int> unified_type;
  typedef qi::rule<std::string::iterator, unified_type() > unified_rule;
  
  unified_rule rstring = +(qi::char_ - '.');
  unified_rule rint    = qi::int_;
  
  unified_rule combine = rstring | rint;