example1.y

来自「学习lemon语法分析的windows程序」· Y 代码 · 共 69 行

/* Copyright (GPL) 2004 [e-mail] or [e-mail]

  Simple lemon parser  example.

  
    $ ./lemon example1.y                          

  The above statement will create example1.c.

  The command below  adds  main and the
  necessary "Parse" calls to the
  end of this example1.c.


    $ cat <<EOF >>example1.c                      
    int main()                                    
    {                                             
      void* pParser = ParseAlloc (malloc);        
      Parse (pParser, INTEGER, 1);                
      Parse (pParser, PLUS, 0);                   
      Parse (pParser, INTEGER, 2);                
      Parse (pParser, 0, 0);                      
      ParseFree(pParser, free );                  
     }                                            
    EOF                                           
            

     $ g++ -o ex1 example1.c                                      
     $ ./ex1

  See the Makefile, as most all of this is
  done automatically.
  
  Downloads:
  http://prdownloads.sourceforge.net/souptonuts/lemon_examples.tar.gz?download

*/

%token_type {int}  
   
%left PLUS MINUS.   
%left DIVIDE TIMES.  
   
%include {   
#include <iostream>  
#include "example1.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; }