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所以我目前正在为 C++ 的一个子集构建一个解析器。到目前为止，我的语法生成的解析器：

-- A program is a sequence of definitions

PDefs . Program ::= [Def] ; 

-- Terminators
terminator Def "" ;
terminator Id "" ;
terminator Stm "" ;

-- Seperators 
separator Arg "," ;
separator Exp ""; 

-- Constructs ignored by the parser
comment "//" ;
comment "/*" "*/" ;
comment "#" ;

-- Function definition 
DFun . Def                              ::= DFunPrefix Type Id "(" [Arg] ")" Body ; 

-- Function prefixes
DFunWithPrefix . DFunPrefix             ::= "inline" ;
DFunWithoutPrefix . DFunPrefix          ::= "" ; 

-- Function body 
FuncBody . Body                         ::= "{" [Stm] "}" ; 
FuncEmptyBody . Body                    ::= ";" ;

-- Id's
token Id (letter (letter | digit | '_')*) ;

-- Argument declarations 
ArgDecl . Arg                           ::= ASpecifier Type ";" ;
ArgDeclId . Arg                         ::= ASpecifier Type Id ";" ;
ArgDeclInit . Arg                       ::= ASpecifier Type Id "=" Exp ";" ;
ArgDeclList .  Arg                      ::= ASpecifier Type [Arg] ";" ;

-- Argument specifiers 
NoASpecifier . ASpecifier               ::= "" ;
ConstASpecifier . ASpecifier            ::= "const" ;

-- Statements
StmExpr . Stm                           ::= Exp ";" ;
StmDecl . Stm                           ::= Type Id ";" ; 
StmDeclInit . Stm                       ::= Type Id "=" Exp ";" ;
StmDeclList . Stm                       ::= Type [Id] ";" ; 

ReturnStm . Stm                         ::= "return" Exp ";" ;
ReturnNoneStm . Stm                     ::= "return" ";" ;

-- Types 
TypeInt . Type                          ::= "int" ;
TypeDouble . Type                       ::= "double" ; 
TypeChar . Type                         ::= "char" ;
TypeString . Type                       ::= "string" ; 
TypeBool . Type                         ::= "bool" ;
TypeVoid . Type                         ::= "void" ; 

-- Expressions
-- Atomic 
ExpId . Exp15                           ::= Id ;
ExpInt . Exp15                          ::= Integer ;
ExpDouble . Exp15                       ::= Double ;
ExpChar . Exp15                         ::= Char ; 
ExpString . Exp15                       ::= String ;
ExpBoolTrue . Exp15                     ::= "true" ;
ExpBoolFalse . Exp15                    ::= "false" ;

-- Non-Atomic
ExpQualifiedConst . Exp15               ::= Id "::" Id ;
ExpLShift . Exp10                       ::= Exp10 "<<" Exp11 ;
ExpRShift . Exp10                       ::= Exp10 ">>" Exp11 ; 

coercions Exp 15;

这能够解析以下简单的 hello world 程序：

// hello world in c++
#include <iostream>

int main()
{
    std::cout << "Hello, stackoverflow!" << std::endl;
    return 0;
}

只有 2 个班次/减少冲突，我很高兴

不，我更进一步，想尝试解析这个程序

// ask for a person's favorite fruit and output it to the console
#include <iostream>
#include <string>

int main()
{
    // ask for a fruit
    std::cout << "Please enter your favorite fruit: ";

    
    std::string fruit;     
    std::cin >> fruit;     

    // output
    std::cout << "The following fruit is the most delicious, " << fruit  << "!" << std::endl;
    return 0;
}

由于第 11 行，这显然不起作用，但我想添加：

ExpQualifiedConstExp.   Exp15 ::= Id "::" Id Exp;

会解决这个问题，但它没有，我不知道为什么。它实际上是如何工作的？

4

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