I have a lexer and based on that lexer I now want to create a grammar that used the tokens generated by this lexer. I tried adapting some examples that I found and now I have something that compiles and works at least a little bit, but one of my tests that should fail does not. Now I want to know why and I also want to know what I'm actually doing there (I want to understand - I just copied some code from some examples but that doesn't really improve the understanding much).
Lexer:
#include <boost/spirit/include/lex_lexertl.hpp>
namespace lex = boost::spirit::lex;
enum LexerIDs { ID_IDENTIFIER, ID_WHITESPACE, ID_INTEGER, ID_FLOAT, ID_PUNCTUATOR };
template <typename Lexer>
struct custom_lexer : lex::lexer<Lexer>
{
custom_lexer()
: identifier("[a-zA-Z_][a-zA-Z0-9_]*")
, white_space("[ \\t\\n]+")
, integer_value("[1-9][0-9]*")
, hex_value("0[xX][0-9a-fA-F]+")
, float_value("[0-9]*\\.[0-9]+([eE][+-]?[0-9]+)?")
, float_value2("[0-9]+\\.([eE][+-]?[0-9]+)?")
, punctuator("\\[|\\]|\\(|\\)|\\.|&>|\\*\\*|\\*|\\+|-|~|!|\\/|%|<<|>>|<|>|<=|>=|==|!=|\\^|&|\\||\\^\\^|&&|\\|\\||\\?|:|,")// [ ] ( ) . &> ** * + - ~ ! / % << >> < > <= >= == != ^ & | ^^ && || ? : ,
{
using boost::spirit::lex::_start;
using boost::spirit::lex::_end;
this->self.add
(identifier, ID_IDENTIFIER)
/*(white_space, ID_WHITESPACE)*/
(integer_value, ID_INTEGER)
(hex_value, ID_INTEGER)
(float_value, ID_FLOAT)
(float_value2, ID_FLOAT)
(punctuator, ID_PUNCTUATOR);
this->self("WS") = white_space;
}
lex::token_def<std::string> identifier;
lex::token_def<lex::omit> white_space;
lex::token_def<int> integer_value;
lex::token_def<int> hex_value;
lex::token_def<double> float_value;
lex::token_def<double> float_value2;
lex::token_def<> punctuator;
};
Grammar:
namespace qi = boost::spirit::qi;
namespace lex = boost::spirit::lex;
template< typename Iterator, typename Lexer>
struct custom_grammar : qi::grammar<Iterator, qi::in_state_skipper<Lexer>>
{
template< typename TokenDef >
custom_grammar(const TokenDef& tok) : custom_grammar::base_type(ges)
{
ges = qi::token(ID_INTEGER) | qi::token(ID_FLOAT);
BOOST_SPIRIT_DEBUG_NODE(ges);
debug(ges);
}
qi::rule<Iterator, qi::in_state_skipper<Lexer>> ges;
};
And example:
BOOST_AUTO_TEST_CASE(BasicGrammar)
{
namespace lex = boost::spirit::lex;
namespace qi = boost::spirit::qi;
std::string test("1234 56");
typedef lex::lexertl::token<char const*, lex::omit, boost::mpl::true_> token_type;
typedef lex::lexertl::lexer<token_type> lexer_type;
typedef custom_lexer<lexer_type>::iterator_type iterator_type;
custom_lexer<lexer_type> my_lexer;
custom_grammar<iterator_type, custom_lexer<lexer_type>::lexer_def> my_grammar(my_lexer);
char const* first = test.c_str();
char const* last = &first[test.size()];
lexer_type::iterator_type iter = my_lexer.begin(first, last);
lexer_type::iterator_type end = my_lexer.end();
bool r = qi::phrase_parse(iter,end,my_grammar, qi::in_state( "WS" )[ my_lexer.self ]);
BOOST_CHECK(r);
}
My assumption is that this returns true because the whitespace is skipped - because auf qi::in_state("WS"). Is that true? Additionally, I know how I can output additional tokens for whitespace - but then I don't know what to put at the location where the qi::in_stat is now - without it it isn't working.
Any ideas what I can improve regarding the structure? Why is the debug output so funny?
<ges>
<try>[]</try>
<success></success>
<attributes>[]</attributes>
</ges>
Thank you for your help.
Regards
Tobias
You parser isn't failing, but no it isn't 'silently' skipping the whitespace either (it parses only one non-whitespace token, anyway).
In fact, a property of *phrase_parse family of Spirit APIs is that it may not match the full input. In fact, this is why it takes the first iterator by reference: after parsing the iterator will indicate where parsing stopped.
I have changed a few bits around so you can easily access the source iterator, by using lex::tokenize_and_phrase_parse instead of qi::phrase_parse on lexer_tokens:
Iterator first = test.c_str();
Iterator last = &first[test.size()];
bool r = lex::tokenize_and_phrase_parse(first,last,my_lexer,my_grammar,qi::in_state( "WS" )[ my_lexer.self ]);
std::cout << std::boolalpha << r << "\n";
std::cout << "Remaining unparsed: '" << std::string(first,last) << "'\n";
The output is:
Remaining unparsed: '56'
Here is a full working example (note I also changed the second parameter of the grammar class to be the Skipper directly, which is more typical for Spirit grammars):
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/lex_lexertl.hpp>
namespace qi = boost::spirit::qi;
namespace lex = boost::spirit::lex;
enum LexerIDs { ID_IDENTIFIER, ID_WHITESPACE, ID_INTEGER, ID_FLOAT, ID_PUNCTUATOR };
template <typename Lexer>
struct custom_lexer : lex::lexer<Lexer>
{
custom_lexer()
: identifier ("[a-zA-Z_][a-zA-Z0-9_]*")
, white_space ("[ \\t\\n]+")
, integer_value ("[1-9][0-9]*")
, hex_value ("0[xX][0-9a-fA-F]+")
, float_value ("[0-9]*\\.[0-9]+([eE][+-]?[0-9]+)?")
, float_value2 ("[0-9]+\\.([eE][+-]?[0-9]+)?")
, punctuator ("\\[|\\]|\\(|\\)|\\.|&>|\\*\\*|\\*|\\+|-|~|!|\\/|%|<<|>>|<|>|<=|>=|==|!=|\\^|&|\\||\\^\\^|&&|\\|\\||\\?|:|,")// [ ] ( ) . &> ** * + - ~ ! / % << >> < > <= >= == != ^ & | ^^ && || ? : ,
{
using boost::spirit::lex::_start;
using boost::spirit::lex::_end;
this->self.add
(identifier , ID_IDENTIFIER)
/*(white_space , ID_WHITESPACE)*/
(integer_value, ID_INTEGER)
(hex_value , ID_INTEGER)
(float_value , ID_FLOAT)
(float_value2 , ID_FLOAT)
(punctuator , ID_PUNCTUATOR);
this->self("WS") = white_space;
}
lex::token_def<std::string> identifier;
lex::token_def<lex::omit> white_space;
lex::token_def<int> integer_value;
lex::token_def<int> hex_value;
lex::token_def<double> float_value;
lex::token_def<double> float_value2;
lex::token_def<> punctuator;
};
template< typename Iterator, typename Skipper>
struct custom_grammar : qi::grammar<Iterator, Skipper>
{
template< typename TokenDef >
custom_grammar(const TokenDef& tok) : custom_grammar::base_type(ges)
{
ges = qi::token(ID_INTEGER) | qi::token(ID_FLOAT);
BOOST_SPIRIT_DEBUG_NODE(ges);
}
qi::rule<Iterator, Skipper > ges;
};
int main()
{
std::string test("1234 56");
typedef char const* Iterator;
typedef lex::lexertl::token<Iterator, lex::omit, boost::mpl::true_> token_type;
typedef lex::lexertl::lexer<token_type> lexer_type;
typedef qi::in_state_skipper<custom_lexer<lexer_type>::lexer_def> skipper_type;
typedef custom_lexer<lexer_type>::iterator_type iterator_type;
custom_lexer<lexer_type> my_lexer;
custom_grammar<iterator_type, skipper_type> my_grammar(my_lexer);
Iterator first = test.c_str();
Iterator last = &first[test.size()];
bool r = lex::tokenize_and_phrase_parse(first,last,my_lexer,my_grammar,qi::in_state( "WS" )[ my_lexer.self ]);
std::cout << std::boolalpha << r << "\n";
std::cout << "Remaining unparsed: '" << std::string(first,last) << "'\n";
}