In boost::spirit::lex, how do I add tokens with a semantic action and a token ID?

Question

I know how to add token definitions with an identifier:

this->self.add(identifier, ID_IDENTIFIER);

And I know how to add token definitions with a semantic action:

this->self += whitespace [ lex::_pass = lex::pass_flags::pass_ignore ];

Unfortunately this doesn't work:

this->self.add(whitespace
                   [ lex::_pass = lex::pass_flags::pass_ignore ],
               ID_IDENTIFIER);

It gives an error that the token can't be converted to a string (!?):

_{error C2664: 'const boost::spirit::lex::detail::lexer_def_>::adder &boost::spirit::lex::detail::lexer_def_>::adder::operator ()(wchar_t,unsigned int) const' : cannot convert argument 1 from 'const boost::proto::exprns_::expr' to 'const std::basic_string,std::allocator> &'}

Interestingly, the adder in lexer.hpp has an operator () which takes an action as a third parameter – but it's commented out in my version of boost (1.55.0). Does this work in newer versions?

In the absence of this, how would I add token definitions with a semantic action and an ID to the lexer?

Answer 1

Looking at the header files it seems that there are at least two possible approaches:

• You can use token_def's id member function in order to set the id after you have defined your token:

  ellipses = "\\.\\.\\.";
  ...
  ellipses.id(ID_ELLIPSES);
  

• You can use token_def's two parameters constructor when you define your token:

  number = lex::token_def<>("[0-9]+", ID_NUMBER);
  

And then you can simply add your semantic actions as you did before:

this->self = ellipses[phx::ref(std::cout) << "Found ellipses.\n"] | '(' | ')' | number[phx::ref(std::cout) << "Found: " << phx::construct<std::string>(lex::_start, lex::_end) << '\n'];

The code below is based on Boost.Spirit.Lex example3.cpp with minor changes (marked with //CHANGED) to achieve what you want.

Full Sample (Running on rextester)

#include <iostream>
#include <string>

#include <boost/config/warning_disable.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/lex_lexertl.hpp>
#include <boost/spirit/include/phoenix.hpp>




using namespace boost::spirit;
namespace phx = boost::phoenix;

enum token_id //ADDED
{
    ID_ELLIPSES = lex::min_token_id + 1,
    ID_NUMBER
};

///////////////////////////////////////////////////////////////////////////////
//  Token definition
///////////////////////////////////////////////////////////////////////////////
template <typename Lexer>
struct example3_tokens : lex::lexer<Lexer>
{
    example3_tokens()
    {
        // define the tokens to match
        ellipses = "\\.\\.\\.";
        number = lex::token_def<>("[0-9]+", ID_NUMBER); //CHANGED

        ellipses.id(ID_ELLIPSES); //CHANGED

        // associate the tokens and the token set with the lexer
        this->self = ellipses[phx::ref(std::cout) << "Found ellipses.\n"] | '(' | ')' | number[phx::ref(std::cout) << "Found: " << phx::construct<std::string>(lex::_start, lex::_end) << '\n']; //CHANGED

        // define the whitespace to ignore (spaces, tabs, newlines and C-style 
        // comments)
        this->self("WS") 
            =   lex::token_def<>("[ \\t\\n]+")          // whitespace
            |   "\\/\\*[^*]*\\*+([^/*][^*]*\\*+)*\\/"   // C style comments
            ;
    }

    // these tokens expose the iterator_range of the matched input sequence
    lex::token_def<> ellipses, identifier, number;
};

///////////////////////////////////////////////////////////////////////////////
//  Grammar definition
///////////////////////////////////////////////////////////////////////////////
template <typename Iterator, typename Lexer>
struct example3_grammar 
  : qi::grammar<Iterator, qi::in_state_skipper<Lexer> >
{
    template <typename TokenDef>
    example3_grammar(TokenDef const& tok)
      : example3_grammar::base_type(start)
    {
        start 
            =  +(couplet | qi::token(ID_ELLIPSES)) //CHANGED
            ;

        //  A couplet matches nested left and right parenthesis.
        //  For example:
        //    (1) (1 2) (1 2 3) ...
        //    ((1)) ((1 2)(3 4)) (((1) (2 3) (1 2 (3) 4))) ...
        //    (((1))) ...
        couplet
            =   qi::token(ID_NUMBER) //CHANGED
            |   '(' >> +couplet >> ')'
            ;

        BOOST_SPIRIT_DEBUG_NODE(start);
        BOOST_SPIRIT_DEBUG_NODE(couplet);
    }

    qi::rule<Iterator, qi::in_state_skipper<Lexer> > start, couplet;
};

///////////////////////////////////////////////////////////////////////////////
int main()
{
    // iterator type used to expose the underlying input stream
    typedef std::string::iterator base_iterator_type;

    // This is the token type to return from the lexer iterator
    typedef lex::lexertl::token<base_iterator_type> token_type;

    // This is the lexer type to use to tokenize the input.
    // Here we use the lexertl based lexer engine.
    typedef lex::lexertl::actor_lexer<token_type> lexer_type; //CHANGED

    // This is the token definition type (derived from the given lexer type).
    typedef example3_tokens<lexer_type> example3_tokens;

    // this is the iterator type exposed by the lexer 
    typedef example3_tokens::iterator_type iterator_type;

    // this is the type of the grammar to parse
    typedef example3_grammar<iterator_type, example3_tokens::lexer_def> example3_grammar;

    // now we use the types defined above to create the lexer and grammar
    // object instances needed to invoke the parsing process
    example3_tokens tokens;                         // Our lexer
    example3_grammar calc(tokens);                  // Our parser

    std::string str ="(1) (1 2) (1 2 3) ... ((1)) ((1 2)(3 4)) (((1) (2 3) (1 2 (3) 4))) ... (((1))) ..."; //CHANGED

    // At this point we generate the iterator pair used to expose the
    // tokenized input stream.
    std::string::iterator it = str.begin();
    iterator_type iter = tokens.begin(it, str.end());
    iterator_type end = tokens.end();

    // Parsing is done based on the token stream, not the character 
    // stream read from the input.
    // Note how we use the lexer defined above as the skip parser.
    bool r = qi::phrase_parse(iter, end, calc, qi::in_state("WS")[tokens.self]);

    if (r && iter == end)
    {
        std::cout << "-------------------------\n";
        std::cout << "Parsing succeeded\n";
        std::cout << "-------------------------\n";
    }
    else
    {
        std::cout << "-------------------------\n";
        std::cout << "Parsing failed\n";
        std::cout << "-------------------------\n";
    }

    std::cout << "Bye... :-) \n\n";
    return 0;
}