Re: X3: How to parse "text" | "texture" into variant<text, texture> ?

On Sun, 14 Feb 2016 04:18:44 -0800 (PST)
Mike Gresens <[email protected]> wrote:

> Hi,
> 
> some code here:
> 
> #include <boost/spirit/home/x3.hpp>
> #include <boost/variant.hpp>
> #include <boost/fusion/include/adapt_struct.hpp>
> #include <string>
> #include <iostream>
> 
> namespace x3 = boost::spirit::x3;
> 
> struct text_t {};
> struct texture_t {};
> typedef boost::variant<text_t, texture_t> object_t;
> typedef std::string::const_iterator iterator;
> 
> BOOST_FUSION_ADAPT_STRUCT(text_t);
> BOOST_FUSION_ADAPT_STRUCT(texture_t);
> 
> const x3::rule<class object_rule, object_t> object_rule("object");
> const x3::rule<class text_rule, text_t> text_rule("text");
> const x3::rule<class texture_rule, texture_t> texture_rule("texture");
> 
> const auto object_rule_def = text_rule | texture_rule;
> const auto text_rule_def = x3::lit("text") > x3::lit('{') >
> x3::lit('}'); const auto texture_rule_def = x3::lit("texture") >
> x3::lit('{') > x3::lit('}');
> 
> BOOST_SPIRIT_DEFINE(object_rule, text_rule, texture_rule);
> 
> int main()
> {
> 	const std::string text("text {}");
> 	const std::string texture("texture {}");
> 	object_t object;
> 	try
> 	{
> 		x3::phrase_parse(text.begin(), text.end(),
> object_rule, x3::space, object); // OK
> 		x3::phrase_parse(texture.begin(), texture.end(),
> object_rule, x3::space, object); // Failure
> 	}
> 	catch (const x3::expectation_failure<iterator>& failure)
> 	{
> 		std::cout << failure.what() << " : " <<
> failure.which() << " : " << *failure.where() << std::endl;
> 	}
> }
> 
> So how can I parse "text" | "texture" into the object variant?
> 
> Thanks,
> Mike...
> 

List texture first. The parser generated is exactly like a C++ `||`
expression in that the left side will be evaluated first.
Alternatively, you could do:
    `lit("text") >> ((lit("ure") >> ...) | (eps >> ... ))`
which is less readable, but eliminates backtracking.

Lee


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