b.y

Lemon是一个C或者C++语言的LALR(1)语法分析器生成器。它和“bison”与“yacc”的功能是一样的

%token_type {int}  
   
%left PLUS MINUS.   
%left DIVIDE TIMES.  
   
%include { 
#include <stdio.h>  
#include <iostream>  
#include "b.h"
}  
   
%syntax_error {  
  std::cout << "Syntax error!" << std::endl;  
}   
   
program ::= expr(A).   { std::cout << "Result=" << A << std::endl; }  
   
expr(A) ::= expr(B) MINUS  expr(C).   { A = B - C; }  
expr(A) ::= expr(B) PLUS  expr(C).   { A = B + C; }  
expr(A) ::= expr(B) TIMES  expr(C).   { A = B * C; }  
expr(A) ::= expr(B) DIVIDE expr(C).  { 

         if(C != 0){
           A = B / C;
          }else{
           std::cout << "divide by zero" << std::endl;
           }
}  /* end of DIVIDE */

expr(A) ::= INTEGER(B). { A = B; } 

%code {
    int main()                                    
    { 
      yyTraceFILE = stdout;//fopen("Trace.txt","wb");
      void* pParser = ParseAlloc (malloc);        
      Parse (pParser, INTEGER, 1);                
      Parse (pParser, PLUS, 0);                   
      Parse (pParser, INTEGER, 2); 
      Parse (pParser, TIMES, 0);
      Parse (pParser, INTEGER, 3);       
      Parse (pParser, 0, 0);                      
      ParseFree(pParser, free ); 
     } 
}