CODEWITHSUNDEEP
c++boost-spiritrule
user1447257
user1447257

Reputation:

Boost spirit or order

I would like to create a boost spirit rule that parses a string and an float. The strings I would like to parse are formatted like this:

(str astring)(n 123)

or could also be in another order:

(n 123)(str astring)

I would like to create a rule with an attribute of following type:

qi::rule<Iter, boost::fusion::vector<std::string, float>, ascii::space_type> hj;

So far this is my code:

qi::rule<Iter, std::string(), ascii::space_type> attr;
attr = lexeme[*alnum];

qi::rule<Iter, boost::fusion::vector<std::string, float>, ascii::space_type> hj;
hj = (
         '(' >> lit("str") >> attr(/*put this at position 0*/) >> ')'
     |
         '(' >> lit("n") >> float_[/*put this at position 1*/] >> ')'
     );

Obviously, this does not compile (boost deducts another attribute type). How can I implement this, especially, what would I put in the commented code?

Upvotes: 2

Views: 158

Answers (1)

sbabbi
sbabbi

Reputation: 11181

You can use the permutation operator ^. Minimum working example:

boost::fusion::vector<std::string,float> ans;
bool res = phrase_parse(first,last,
            (lit("(") >> lit("str") >> lexeme[*ascii::alnum] >> lit(")") ) ^
            (lit("(") >> lit("n") >> float_ >> lit(")") ),
            ascii::space,ans);

This solution is described with more detail here.

Upvotes: 2

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