build error with boost spirit grammar (boost 1.43

Question

I'm having issues getting a small spirit/qi grammar to compile. i am using boost 1.43 and g++ 4.4.1.

the input grammar header: the build error seems to be pointing to the definition of the 'instruction' rule, maybe it is the '[sp::_val = sp::_1]' that somehow brokes it but this is more or less based on what the spirit documentation tutorials are doing with the xml node parser

inputGrammar.h

#include <boost/config/warning_disable.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix_core.hpp>
#include <boost/spirit/include/phoenix_operator.hpp>
#include <boost/spirit/include/phoenix_fusion.hpp>
#include <boost/spirit/include/phoenix_stl.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/variant/recursive_variant.hpp>
#include <boost/foreach.hpp>

#include <iostream>
#include <fstream>
#include <string>
#include <vector>

namespace sp = boost::spirit;
namespace qi = boost::spirit::qi;
using namespace boost::spirit::ascii;
//using namespace boost::spirit::arg_names;

namespace fusion = boost::fusion;
namespace phoenix = boost::phoenix;

using phoenix::at_c;
using phoenix::push_back;


template< typename Iterator , typename ExpressionAST >
struct InputGrammar : qi::grammar<Iterator, ExpressionAST(), space_type> {

    InputGrammar() : InputGrammar::base_type( block ) {
        tag = sp::lexeme[+(alpha)        [sp::_val += sp::_1]];//[+(char_ - '<')        [_val += _1]];

        block = sp::lit("block") [ at_c<0>(sp::_val) = sp::_1]
                >> "(" >> *instruction[ push_back( at_c<1>(sp::_val) , sp::_1 ) ]
                >> ")";

        command = tag   [ at_c<0>(sp::_val) = sp::_1]
                                >> "(" >> *instruction [ push_back( at_c<1>(sp::_val) , sp::_1 )]
                                >> ")";

        instruction = ( command | tag ) [sp::_val = sp::_1]; //build error seems to be happening here
    }
    qi::rule< Iterator , std::string() , space_type > tag;
    qi::rule< Iterator , ExpressionAST() , space_type > block;
    qi::rule< Iterator , ExpressionAST() , space_type > function_def;
    qi::rule< Iterator , ExpressionAST() , space_type > command;
    qi::rule< Iterator , ExpressionAST() , space_type > instruction;
};

the test build program:

#include <iostream>
#include <string>
#include <vector>
using namespace std;

//my grammar
#include <InputGrammar.h>

struct MockExpressionNode {
    std::string name;
    std::vector< MockExpressionNode > operands;

    typedef std::vector< MockExpressionNode >::iterator iterator;
    typedef std::vector< MockExpressionNode >::const_iterator const_iterator;

    iterator begin() { return operands.begin(); }
    const_iterator begin() const { return operands.begin(); }
    iterator end() { return operands.end(); }
    const_iterator end() const { return operands.end(); }

    bool is_leaf() const {
        return ( operands.begin() == operands.end() );
    }
};


BOOST_FUSION_ADAPT_STRUCT(
    MockExpressionNode,
    (std::string, name)
    (std::vector<MockExpressionNode>, operands)
)

int const tabsize = 4;

void tab(int indent)
{
    for (int i = 0; i < indent; ++i)
        std::cout << ' ';
}

template< typename ExpressionNode >
struct ExpressionNodePrinter
{
    ExpressionNodePrinter(int indent = 0)
      : indent(indent)
    {
    }

    void operator()(ExpressionNode const& node) const {
        cout << " tag: " << node.name << endl;
        for (int i=0 ; i < node.operands.size() ; i++ ) {
            tab( indent ); cout << " arg "<<i<<": "; ExpressionNodePrinter(indent + 2)( node.operands[i]); cout << endl;
        }
    }

    int indent;
};

int test() {
 MockExpressionNode root;
    InputGrammar< string::const_iterator , MockExpressionNode > g;
    std::string litA = "litA";
    std::string litB = "litB";
    std::string litC = "litC";
    std::string litD = "litD";
    std::string litE = "litE";
    std::string litF = "litF";
    std::string source = litA+"( "+litB+" ,"+litC+" , "+ litD+" ( "+litE+", "+litF+" ) "+ " )";
    string::const_iterator iter = source.begin();
    string::const_iterator end = source.end();
    bool r = qi::phrase_parse( iter , end , g , space , root );
    ExpressionNodePrinter< MockExpressionNode > np;
    np( root );
};

int main() {
   test();
}

finally, the build error is the following:

(the full error trace is 20 times bigger than the allowed size for a stackoverflow question, so i posted the full version of it at http://codepad.org/Q74IVCUc)

/usr/bin/make -f nbproject/Makefile-linux_amd64_devel.mk SUBPROJECTS= .build-conf
make[1]: se ingresa al directorio `/home/mineq/NetBeansProjects/InputParserTests'
/usr/bin/make  -f nbproject/Makefile-linux_amd64_devel.mk dist/linux_amd64_devel/GNU-Linux-x86/vpuinputparsertests
make[2]: se ingresa al directorio `/home/mineq/NetBeansProjects/InputParserTests'
mkdir -p build/linux_amd64_devel/GNU-Linux-x86
rm -f build/linux_amd64_devel/GNU-Linux-x86/tests_main.o.d
g++ `llvm-config --cxxflags` `pkg-config --cflags unittest-cpp` `pkg-config --cflags boost-1.43` `pkg-config --cflags boost-coroutines`    -c -g -I../InputParser -MMD -MP -MF build/linux_amd64_devel/GNU-Linux-x86/tests_main.o.d -o build/linux_amd64_devel/GNU-Linux-x86/tests_main.o tests_main.cpp
                 from /home/mineq/third_party/boost_1_43_0/boost/spirit/include/phoenix_operator.hpp:11,
                 from ../InputParser/InputGrammar.h:14,
                 from tests_main.cpp:14:
/home/mineq/third_party/boost_1_43_0/boost/spirit/home/phoenix/operator/self.hpp: In instantiation of ‘const int boost::phoenix::result_of_assign<MockExpressionNode&, boost::variant<MockExpressionNode, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_>&>::size’:
In file included from /home/mineq/third_party/boost_1_43_0/boost/spirit/home/phoenix/operator.hpp:16,
/home/mineq/third_party/boost_1_43_0/boost/spirit/home/phoenix/operator/self.hpp:27:   instantiated from ‘const int boost::phoenix::result_of_assign<MockExpressionNode&, boost::variant<MockExpressionNode, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_>&>::index’
/home/mineq/third_party/boost_1_43_0/boost/spirit/home/phoenix/operator/self.hpp:27:   instantiated from ‘boost::phoenix::result_of_assign<MockExpressionNode&, boost::variant<MockExpressionNode, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_>&>’
/home/mineq/third_party/boost_1_43_0/boost/mpl/eval_if.hpp:38:   instantiated from ‘boost::mpl::eval_if<boost::mpl::or_<boost::phoenix::is_actor<MockExpressionNode&>, boost::phoenix::is_actor<boost::variant<MockExpressionNode, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_>&>, mpl_::bool_<false>, mpl_::bool_<false>, mpl_::bool_<false> >, boost::phoenix::re_curry<boost::phoenix::assign_eval, MockExpressionNode&, boost::variant<MockExpressionNode, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_>&, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_>, boost::phoenix::result_of_assign<MockExpressionNode&, boost::variant<MockExpressionNode, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_>&> >’
/home/mineq/third_party/boost_1_43_0/boost/spirit/home/phoenix/operator/self.hpp:69:   instantiated from ‘boost::phoenix::assign_eval::result<boost::phoenix::basic_environment<boost::fusion::vector1<boost::variant<MockExpressionNode, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_>&>, boost::spirit::context<boost::fusion::cons<MockExpressionNode&, boost::fusion::nil>, boost::fusion::vector0<void> >, bool, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_>, boost::spirit::attribute<0>, boost::spirit::argument<0> >’
/home/mineq/third_party/boost_1_43_0/boost/spirit/home/phoenix/core/detail/composite_eval.hpp:89:   instantiated from ‘boost::phoenix::detail::composite_eval<2>::result<boost::phoenix::composite<boost::phoenix::assign_eval, boost::fusion::vector<boost::spirit::attribute<0>, boost::spirit::argument<0>, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_> >, boost::phoenix::basic_environment<boost::fusion::vector1<boost::variant<MockExpressionNode, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_>&>, boost::spirit::context<boost::fusion::cons<MockExpressionNode&, boost::fusion::nil>, boost::fusion::vector0<void> >, bool, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_> >’
/home/mineq/third_party/boost_1_43_0/boost/spirit/home/phoenix/core/composite.hpp:61:   instantiated from ‘boost::phoenix::composite<boost::phoenix::assign_eval, boost::fusion::vector<boost::spirit::attribute<0>, boost::spirit::argument<0>, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_> >::result<boost::phoenix::basic_environment<boost::fusion::vector1<boost::variant<MockExpressionNode, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_>&>, boost::spirit::context<boost::fusion::cons<MockExpressionNode&, boost::fusion::nil>, boost::fusion::vector0<void> >, bool, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_> >’
/home/mineq/third_party/boost_1_43_0/boost/spirit/home/phoenix/core/actor.hpp:56:   instantiated from ‘boost::phoenix::eval_result<boost::phoenix::composite<boost::phoenix::assign_eval, boost::fusion::vector<boost::spirit::attribute<0>, boost::spirit::argument<0>, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_> >, boost::phoenix::basic_environment<boost::fusion::vector1<boost::variant<MockExpressionNode, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_>&>, boost::spirit::context<boost::fusion::cons<MockExpressionNode&, boost::fusion::nil>, boost::fusion::vector0<void> >, bool, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_> >’
/home/mineq/third_party/boost_1_43_0/boost/spirit/home/phoenix/core/actor.hpp:65:   instantiated from ‘boost::phoenix::actor<boost::phoenix::composite<boost::phoenix::assign_eval, boost::fusion::vector<boost::spirit::attribute<0>, boost::spirit::argument<0>, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_> > >::result<boost::phoenix::actor<boost::phoenix::composite<boost::phoenix::assign_eval, boost::fusion::vector<boost::spirit::attribute<0>, boost::spirit::argument<0>, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_> > >(boost::fusion::vector1<boost::variant<MockExpressionNode, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_>&>&, boost::spirit::context<boost::fusion::cons<MockExpressionNode&, boost::fusion::nil>, boost::fusion::vector0<void> >&, bool&)>’
/home/mineq/third_party/boost_1_43_0/boost/spirit/home/support/action_dispatch.hpp:44:   instantiated from ‘bool boost::spirit::traits::action_dispatch<Component>::operator()(const boost::phoenix::actor<Eval>&, Attribute&, Context&) [with Eval = boost::phoenix::composite<boost::phoenix::assign_eval, boost::fusion::vector<boost::spirit::attribute<0>, boost::spirit::argument<0>, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_> >, Attribute = boost::variant<MockExpressionNode, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_>, Context = boost::spirit::context<boost::fusion::cons<MockExpressionNode&, boost::fusion::nil>, boost::fusion::vector0<void> >, Component = boost::spirit::qi::alternative<boost::fusion::cons<boost::spirit::qi::reference<const boost::spirit::qi::rule<__gnu_cxx::__normal_iterator<const char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, MockExpressionNode(), boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0l>, boost::fusion::unused_type, boost::fusion::unused_type> >, boost::fusion::cons<boost::spirit::qi::reference<const boost::spirit::qi::rule<__gnu_cxx::__normal_iterator<const char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::string(), boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0l>, boost::fusion::unused_type, boost::fusion::unused_type> >, boost::fusion::nil> > >]’
/home/mineq/third_party/boost_1_43_0/boost/spirit/home/qi/action/action.hpp:62:   instantiated from ‘bool boost::spirit::qi::action<Subject, Action>::parse(Iterator&, const Iterator&, Context&, const Skipper&, Attribute&) const [with Iterator = __gnu_cxx::__normal_iterator<const char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, Context = boost::spirit::context<boost::fusion::cons<MockExpressionNode&, boost::fusion::nil>, boost::fusion::vector0<void> >, Skipper = boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, Attribute = const boost::fusion::unused_type, Subject = boost::spirit::qi::alternative<boost::fusion::cons<boost::spirit::qi::reference<const boost::spirit::qi::rule<__gnu_cxx::__normal_iterator<const char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, MockExpressionNode(), boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0l>, boost::fusion::unused_type, boost::fusion::unused_type> >, boost::fusion::cons<boost::spirit::qi::reference<const boost::spirit::qi::rule<__gnu_cxx::__normal_iterator<const char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::string(), boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0l>, boost::fusion::unused_type, boost::fusion::unused_type> >, boost::fusion::nil> > >, Action = boost::phoenix::actor<boost::phoenix::composite<boost::phoenix::assign_eval, boost::fusion::vector<boost::spirit::attribute<0>, boost::spirit::argument<0>, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_> > >]’
/home/mineq/third_party/boost_1_43_0/boost/spirit/home/qi/nonterminal/detail/parser_binder.hpp:33:   instantiated from ‘bool boost::spirit::qi::detail::parser_binder<Parser, Auto>::call(Iterator&, const Iterator&, Context&, const Skipper&, mpl_::true_) const [with Iterator = __gnu_cxx::__normal_iterator<const char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, Skipper = boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, Context = boost::spirit::context<boost::fusion::cons<MockExpressionNode&, boost::fusion::nil>, boost::fusion::vector0<void> >, Parser = boost::spirit::qi::action<boost::spirit::qi::alternative<boost::fusion::cons<boost::spirit::qi::reference<const boost::spirit::qi::rule<__gnu_cxx::__normal_iterator<const char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, MockExpressionNode(), boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0l>, boost::fusion::unused_type, boost::fusion::unused_type> >, boost::fusion::cons<boost::spirit::qi::reference<const boost::spirit::qi::rule<__gnu_cxx::__normal_iterator<const char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::string(), boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0l>, boost::fusion::unused_type, boost::fusion::unused_type> >, boost::fusion::nil> > >, boost::phoenix::actor<boost::phoenix::composite<boost::phoenix::assign_eval, boost::fusion::vector<boost::spirit::attribute<0>, boost::spirit::argument<0>, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_> > > >, Auto = mpl_::bool_<false>]’
/home/mineq/third_party/boost_1_43_0/boost/spirit/home/qi/nonterminal/detail/parser_binder.hpp:53:   instantiated from ‘bool boost::spirit::qi::detail::parser_binder<Parser, Auto>::operator()(Iterator&, const Iterator&, Context&, const Skipper&) const [with Iterator = __gnu_cxx::__normal_iterator<const char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, Skipper = boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, Context = boost::spirit::context<boost::fusion::cons<MockExpressionNode&, boost::fusion::nil>, boost::fusion::vector0<void> >, Parser = boost::spirit::qi::action<boost::spirit::qi::alternative<boost::fusion::cons<boost::spirit::qi::reference<const boost::spirit::qi::rule<__gnu_cxx::__normal_iterator<const char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, MockExpressionNode(), boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0l>, boost::fusion::unused_type, boost::fusion::unused_type> >, boost::fusion::cons<boost::spirit::qi::reference<const boost::spirit::qi::rule<__gnu_cxx::__normal_iterator<const char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::string(), boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0l>, boost::fusion::unused_type, boost::fusion::unused_type> >, boost::fusion::nil> > >, 
 ...

... more errors but i had to truncate to fit the 30k limit

make[2]: *** [build/linux_amd64_devel/GNU-Linux-x86/tests_main.o] Error 1
make[2]: se sale del directorio `/home/mineq/NetBeansProjects/InputParserTests'
make[1]: *** [.build-conf] Error 2
make[1]: se sale del directorio `/home/mineq/NetBeansProjects/InputParserTests'
make: *** [.build-impl] Error 2
BUILD FAILED (exit value 2, total time: 2m 13s)

Answer 1

Your error message tells you that you want to assign a variant<MockExpressionNode, basic_string> to a MockExpressionNode

The relevant lines are 33 and 34;

[...] error: no match for ‘operator=’ [...] boost::variant<MockExpressionNode, std::basic_string [...]
[...] candidates are: MockExpressionNode& MockExpressionNode::operator=(const MockExpressionNode&) [...]

To understand why this happens we have to look at the definitions. From the definition of a Qi rule, the signature of the returned value is defined by a template parameter. Hence

qi::rule< Iterator , ExpressionAST() , space_type > command;

means that the returned type of a command will be an ExpressionAST (i.e. a MockExpressionNode in your case). Similarly

qi::rule< Iterator , std::string() , space_type > tag;

means that tag will be of type string. Combining this with instruction = (command | tag) means that an instruction is either a string or a MockExpressionNode. This is internally stored as a variant<MockExpressionNode, string>. Finally,

qi::rule< Iterator , ExpressionAST() , space_type > instruction;

implies that the returned type of instruction is again an ExpressionAST (i.e. a MockExpressionNode). This requires the failing assignment from the variant held internally to a MockExpressionNode.

To sum up, you have to provide types in your qi::rules that somewhat "match" the types implied by your grammar in the sense that assignment is possible. Despite all the Boost.Spirit magic, C++ is still a statically typed language after all. For the issue at hand, you either have to supply a fitting operator=, or you have to assign the results of the different rules to different types that support implicit conversion. BTW, you have similar type issues for block and command at the moment. Take a careful look at the mini_xml example in the documentation: how to define types for a recursive structure and how different rules assign to different types depending on the defined grammar (especially rules xml and node).