| // Copyright (c) 2001-2010 Hartmut Kaiser |
| // |
| // Distributed under the Boost Software License, Version 1.0. (See accompanying |
| // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |
| |
| // This example shows how to create a simple lexer recognizing a couple of |
| // different tokens and how to use this with a grammar. This example has a |
| // heavily backtracking grammar which makes it a candidate for lexer based |
| // parsing (all tokens are scanned and generated only once, even if |
| // backtracking is required) which speeds up the overall parsing process |
| // considerably, out-weighting the overhead needed for setting up the lexer. |
| // |
| // Additionally, this example demonstrates, how to define a token set usable |
| // as the skip parser during parsing, allowing to define several tokens to be |
| // ignored. |
| // |
| // This example recognizes couplets, which are sequences of numbers enclosed |
| // in matching pairs of parenthesis. See the comments below to for details |
| // and examples. |
| |
| // #define BOOST_SPIRIT_LEXERTL_DEBUG |
| // #define BOOST_SPIRIT_DEBUG |
| |
| #include <boost/config/warning_disable.hpp> |
| #include <boost/spirit/include/qi.hpp> |
| #include <boost/spirit/include/lex_lexertl.hpp> |
| |
| #include <iostream> |
| #include <fstream> |
| #include <string> |
| |
| #include "example.hpp" |
| |
| using namespace boost::spirit; |
| |
| /////////////////////////////////////////////////////////////////////////////// |
| // Token definition |
| /////////////////////////////////////////////////////////////////////////////// |
| template <typename Lexer> |
| struct example3_tokens : lex::lexer<Lexer> |
| { |
| example3_tokens() |
| { |
| // define the tokens to match |
| ellipses = "\\.\\.\\."; |
| number = "[0-9]+"; |
| |
| // associate the tokens and the token set with the lexer |
| this->self = ellipses | '(' | ')' | number; |
| |
| // 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 | tok.ellipses) |
| ; |
| |
| // 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 |
| = tok.number |
| | '(' >> +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::lexer<token_type> lexer_type; |
| |
| // 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 (read_from_file("example3.input")); |
| |
| // 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 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; |
| } |