c++ - 回复：帮助提升语法

Answer 1

I have redesigned the grammar as follows, and that seem to have fixed the problem:

subst = multi_choice | machine_subst ;

        multi_choice 
                = machine_subst
                >> +( str_p("[]") >> machine_subst )
                ;


        machine_subst
                = (  multi_subst 
                | simple_subst
                | if_select_pre_subst
                | unbounded_choice )[&do_machSubst]
                ;

... ...

multi_subst = ( simple_subst

+( str_p("||") >> simple_subst ) ) [&do_mSubst] ;

        simple_subst
                = (identifier
                >> str_p(":=") >> arith_expr) [&do_sSubst]
                ;

        expression
                = predicate
                | logic_expr
                | arith_expr
                ;

        predicate
                = ( logic_expr 
                >> +( ( str_p("&") >> logic_expr )
                |     ( str_p("OR") >> logic_expr ) ) )[&do_predicate]
                ;

        logic_expr 
                = ( identifier
                >> ( (str_p("<") >> arith_expr)
                | (str_p(">")  >> arith_expr)
                | (str_p("/:")  >> arith_expr)
                | (str_p("<:")  >> arith_expr)
                | (str_p("/<:")  >> arith_expr)
                | (str_p("<<:")  >> arith_expr)
                | (str_p("/<<:")  >> arith_expr)
                | (str_p("<=")  >> arith_expr)
                | (str_p("=")  >> arith_expr)
                | (str_p(">=")  >> arith_expr)
                | (str_p("=>")  >> arith_expr) )
                )  [&do_logicExpr]
                ;

... ... I now use the start rule "subst" for files f1.txt and f2.txt and "expression" for f3.txt and f4.txt.

start() const { return subst; //return machine_subst; //return expression; //return if_select_pre_subst; //return multi_choice; //return unbounded_choice; }

I am still building the grammar up, so if I have any further issues, I will post it.