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

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无人共我
无人共我 2021-02-03 16:52

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

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  •  醉梦人生
    2021-02-03 17:07

    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*> keyword;
      

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

      qi::symbols() >*> 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 unified_type;
      typedef qi::rule unified_rule;
      
      unified_rule rstring = +(qi::char_ - '.');
      unified_rule rint    = qi::int_;
      
      unified_rule combine = rstring | rint;
      

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