Subject: Re: [boost] [spirit][qi] strange attribute composition when using expectation points
From: Hartmut Kaiser (hartmut.kaiser_at_[hidden])
Date: 2010-09-11 08:54:40
> I get a different attribute composition depending on the use of
> expectation points. Here is a small example:
>
> //////////////////////////////////////////////////////////////////////////
> //////////////////////
> //
>
> BOOST_FUSION_DEFINE_STRUCT(
> (client), input,
> (int, index1)
> (std::string, text)
> (int, index2)
> )
>
>
>
> namespace client {
>
>
> namespace fusion = boost::fusion;
> namespace phoenix = boost::phoenix;
> namespace qi = boost::spirit::qi;
> namespace char_enc = boost::spirit::iso8859_1;
>
> template <typename Iterator, typename Skipper>
> struct line_grammar
> : qi::grammar<Iterator, input(), Skipper>
> {
> line_grammar()
> : line_grammar::base_type(line)
> {
> using qi::int_;
> using qi::omit;
> using char_enc::char_;
> using qi::lit;
>
>
> line =
> int_
> >> lit(",")
> #ifdef USE_EXPECTATION_POINT
> > *(char_ - ( "," >> int_ ) ) #else
> >> *(char_ - ( "," >> int_ ) ) #endif
> >> lit(",")
> >> int_
>
> ;
>
> }
>
> qi::rule<Iterator, input(), Skipper > line;
>
> };
>
>
> bool read_line( )
> {
> typedef line_grammar<std::string::const_iterator,
> char_enc::space_type> grammar;
>
> grammar gr; // Our grammar
>
> input line_read;
>
> std::string source = "1,x,2";
> std::string::const_iterator iter = source.begin();
> std::string::const_iterator end = source.end();
> bool r = phrase_parse(iter, end, gr,
> char_enc::space,
> line_read);
>
> return r && iter == end;
> }
>
> }
>
> //
> //////////////////////////////////////////////////////////////////////////
> ///////////////////////////////
>
> If USE_EXPECTATION_POINT is not defined then parsing succeeds and
> line_read == {1, "x", 2 }.
> But if USE_EXPECTATION_POINT is defined then parsing also succeeds but
> line_read == {1, "x\0x2", 0 }.
> So, it seems that expectation points somehow break the semantics of
> attribute composition.
Generally, expectation points in terms of attribute handling do not mix well
with 'normal' sequences. The parser expression
int_ >> *(char_ - ( "," >> int_ ) ) >> int_
exposes as its attribute a tuple<int, vector<char>, int>, while the
expression
int_ > *(char_ - ( "," >> int_ ) ) >> int_
will expose a tuple<tuple<int, vector<char>>, int>, which is the reason for
the problems you're seeing.
Regards Hartmut
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