Dear Tongari, dear all,

I have created the following rule:

qi::rule<std::string::const_iterator, VARTYPE(), ascii::space_type>
varReference =
( (attr(0) >> attr("empty") >> uint_)
| (attr(1) >> identifier >> '[' >> uint_ >> ']')
| (attr(2) >> identifier >> attr(0)) );

Here, VARTYPE is a typedef for
boost::tuple<std::size_t, std::string, std::size_t>, and "identifier"
stands for lexeme[+char_("0-9a-zA-Z_")] as per your suggestion.

The idea is to provide the user with a mode-variable to allow easy
distinction between all three cases, and to fill unused parts of the
tuple with some placeholder (such as "empty" or 0), with the help of
attr(). So the first entry of the tuple represents the mode, the second
the variable name and the third an optional index.

Now, parsing a string like "MY_DPAR_02[3]" yields "emptyMY_DPAR_02" for
the std::string component of the tuple, and "SOME_IPAR_17" results in
"emptySOME_IPAR_17SOME_IPAR_17" . Parsing a single 0 yields the correct
result.

So the parser seems to go through all three components of varReference,
until it finds a matching rule. However, instead of overwriting the
std::string with the string it has found, it appears to concatenate the
strings of all rules it has gone through.

This is a bit mysterious to me and I would appreciate your help.