I am sure this has been asked before, but I am not able to find an answer to my specific question in the archives. I wanted to create a grammar that can accept statements like if_(expr)[ statement-list ].else_[statement-list]. I created a if_expr type using proto::extends, and added a member called else_ to it, of type proto::function, Expr const&>. The code is given below. I am trying to match statements of the above form. Look for if_only_grammar and if_grammar below. The main function has 2 cases, one with just if_ and another with if_ and else_. My grammar matches neither of them. What am I doing wrong? I am quite the newbie to proto, so I am not still able to parse the compiler error message and understand it yet. I will be grateful for any help. Thanks, Manjunath #include #include #include #include <iostream> #include <sstream> #include <string> using namespace boost; using namespace std; unsigned int ids; template<typename VT> struct Var { unsigned int id; Var() { id = ++ids; } }; struct if_fun {}; struct program {}; struct if_then_else {}; struct if_domain; template <typename Expr> struct if_expr : proto::extends { typedef proto::extends base_type; using base_type::operator =; typedef typename proto::result_of::make_expr::type else_type; else_type else_; if_expr(Expr const &e = Expr()) : base_type(e) , else_(proto::make_exprproto::tag::function(if_then_else(), boost::ref(e))) {} }; struct if_domain : proto::domain > { }; struct napl_grammar; struct arith_expr_grammar; struct rel_expr_grammar; struct assign_grammar; struct statement_grammar; struct bb_grammar; struct if_only_grammar : proto::or_< proto::subscript::type>, rel_expr_grammar >, bb_grammar>

{ };

struct if_grammar : proto::or_< if_only_grammar, proto::subscript, if_only_grammar>, bb_grammar>

{ };

struct arith_expr_grammar : proto::or_< proto::plus< arith_expr_grammar, arith_expr_grammar>, proto::minus< arith_expr_grammar, arith_expr_grammar>, proto::multiplies< arith_expr_grammar, arith_expr_grammar>, proto::divides< arith_expr_grammar, arith_expr_grammar>, proto::terminal, proto::terminal<int>, rel_expr_grammar

{ };

struct rel_expr_grammar : proto::or_< proto::less< arith_expr_grammar, arith_expr_grammar>, proto::greater< arith_expr_grammar, arith_expr_grammar>, proto::less_equal< arith_expr_grammar, arith_expr_grammar>, proto::greater_equal< arith_expr_grammar, arith_expr_grammar>, proto::equal_to< arith_expr_grammar, arith_expr_grammar>, proto::not_equal_to< arith_expr_grammar, arith_expr_grammar>, proto::logical_not< rel_expr_grammar>

{ };

struct assign_grammar : proto::or_< proto::assign, arith_expr_grammar>, proto::assign, rel_expr_grammar>

{ };

struct statement_grammar : proto::or_< assign_grammar, if_grammar

{ };

struct bb_grammar : proto::or_< statement_grammar, proto::comma

{ };

struct napl_grammar : proto::or_< proto::terminal<program>, proto::subscript

{ };

template<typename Expr> void check_and_execute(const Expr &e, mpl::true_) { cout << "Program printer TBD.\n"; } template<typename Expr> void check_and_execute(const Expr &e, mpl::false_) { cout << "Should not be here\n"; } template<typename Expr> void check_grammar(const Expr &e) { BOOST_MPL_ASSERT_MSG((proto::matches::value), SYNTAX_NOT_CORRECT, (void)); check_and_execute(e, proto::matches()); //cout << napl_grammar()(e) << "\n"; } int main() { proto::terminal::type i1, i2, i3, i4, i5; proto::terminal<program>::type Program; if_expr::type> if_; int i=4242; check_grammar( Program[ if_(i1 < i2) [ i2 ] ]); /* check_grammar( Program[ if_(i1 < i2) [ i2 ].else_[ i3 ] ]); */ }