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    <p>I think you are looking for 'subrules' (that Spirit V1/classical used to have). These are obsolete now.</p> <p>Have a look at </p> <ul> <li><p>c++11 <code>auto</code> and <code>BOOST_AUTO</code> </p> <pre><code>auto subexpression = int_ &gt;&gt; ',' &gt;&gt; double_; qi::rule&lt;It&gt; rule = "A:" &gt;&gt; subexpression &gt;&gt; "Rest:" &gt;&gt; (subexpression % eol); </code></pre> <p>There used to be issues with using <code>auto</code> on Spirit rules (notably with MSVC) (see <a href="http://boost-spirit.com/home/articles/qi-example/zero-to-60-mph-in-2-seconds/" rel="nofollow">Zero to 60 MPH in 2 seconds!</a> and comments) but I have been informed this (soon) <a href="http://boost.2283326.n4.nabble.com/What-happened-to-subrules-tc4636688.html" rel="nofollow">is no longer an issue</a>: </p> <blockquote> <pre><code>Yep. Anyway,FYI, it's fixed in Spirit-3. You can use auto all you want. Regards, -- Joel de Guzman </code></pre> </blockquote></li> <li><p><a href="http://www.boost.org/doc/libs/1_52_0/libs/spirit/doc/html/spirit/qi/reference/auxiliary/lazy.html" rel="nofollow">qi::lazy</a></p></li> <li><a href="http://www.boost.org/doc/libs/1_52_0/libs/spirit/doc/html/spirit/qi/reference/parser_concepts/nonterminal.html#spirit.qi.reference.parser_concepts.nonterminal._code__phrase_role__identifier___r1__phrase___code_______code__phrase_role__identifier__r10__phrase___code_" rel="nofollow">inherited arguments</a> - introduced in the <a href="http://www.boost.org/doc/libs/1_52_0/libs/spirit/doc/html/spirit/qi/tutorials/mini_xml___asts_.html" rel="nofollow">Mini XML - ASTs</a> tutorial</li> </ul> <p>Here is a proof of concept that passes a common subrule to different 'compound' rules to allow for wrapping in <code>()</code>, <code>[]</code> or <code>{}</code>:</p> <pre><code>#include &lt;boost/spirit/include/qi.hpp&gt; #include &lt;boost/spirit/include/phoenix.hpp&gt; namespace qi = boost::spirit::qi; namespace phx = boost::phoenix; typedef std::string::const_iterator It; template &lt;typename R&gt; void test(const std::string&amp; input, R const&amp; rule) { It f(input.begin()), l(input.end()); bool ok = qi::phrase_parse(f,l,rule,qi::space); std::cout &lt;&lt; "'" &lt;&lt; input &lt;&lt; "'\tparse " &lt;&lt; (ok?"success":"failure") &lt;&lt; "\n"; } int main() { typedef qi::rule&lt;It, qi::space_type&gt; common_rule; typedef qi::rule&lt;It, void(common_rule), qi::space_type&gt; compound_rule; common_rule common = qi::int_; compound_rule in_parens = qi::lit('(') &gt;&gt; qi::_r1 &gt;&gt; ')', in_brackets = qi::lit('[') &gt;&gt; qi::_r1 &gt;&gt; ']', in_braces = qi::lit('{') &gt;&gt; qi::_r1 &gt;&gt; '}'; test("{ 231 }" , in_braces (phx::ref(common )) ); test("{ hello }", in_braces (phx::val("hello")) ); test("( 231 )" , in_parens (phx::ref(common )) ); test("( hello )", in_parens (phx::val("hello")) ); test("[ 231 ]" , in_brackets(phx::ref(common )) ); test("[ hello ]", in_brackets(phx::val("hello")) ); } </code></pre> <p>Output:</p> <pre><code>'{ 231 }' parse success '{ hello }' parse success '( 231 )' parse success '( hello )' parse success '[ 231 ]' parse success '[ hello ]' parse success </code></pre> <p>PS. Note the above is <strong><em>not</em></strong> a typical Spirit grammar. This way doesn't play too well when the 'common' rule would expose different attributes.</p>
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    1. POFactoring out common parts of Spirit rules
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    1. COsehe, thanks for could you answer. Could you finish it? The last word "Also" tells me you had more to say...
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    2. CO@Arkadiy I don't remember anything specific I was going to say. Except maybe the thing about 'auto' that I did add. Cheers
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    3. COQuestion: how do we get from val("hello") to common_rule?
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