/* Copyright (GPL) 2004 or
  Simple lemon parser  example.

    $ ./lemon example2.y                          



%include {   
#include <iostream>  
#include "ex4def.h"
#include "example4.h"

  void token_destructor(Token t)
      std::cout << "In token_destructor t.value= " << t.value << std::endl;
      std::cout << "In token_destructor t.n= " << t.n << std::endl;


%token_type {Token}
%default_type {Token}
%token_destructor { token_destructor($$); }

%type expr {Token}
%type NUM {Token}

%left PLUS MINUS.   
%parse_accept {
  printf("parsing complete!\n\n\n");

%syntax_error {  
  std::cout << "Syntax error!" << std::endl;  
/*  This is to terminate with a new line */
main ::= in.
in ::= .
in ::= in state NEWLINE.

state ::= expr(A).   { 
                        std::cout << "Result.value=" << A.value << std::endl; 
                        std::cout << "Result.n=" << A.n << std::endl; 


expr(A) ::= expr(B) MINUS  expr(C).   { A.value = B.value - C.value; 
                                       A.n = B.n+1  + C.n+1;

expr(A) ::= expr(B) PLUS  expr(C).   { A.value = B.value + C.value; 
                                       A.n = B.n+1  + C.n+1;

expr(A) ::= expr(B) TIMES  expr(C).   { A.value = B.value * C.value;
                                        A.n = B.n+1  + C.n+1;

expr(A) ::= expr(B) DIVIDE expr(C).  { 

         if(C.value != 0){
           A.value = B.value / C.value;
           A.n = B.n+1 + C.n+1;
           std::cout << "divide by zero" << std::endl;
}  /* end of DIVIDE */
expr(A) ::= NUM(B). { A.value = B.value; A.n = B.n+1; }


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Chirico img Mike Chirico, a father of triplets (all girls) lives outside of Philadelphia, PA, USA. He has worked with Linux since 1996, has a Masters in Computer Science and Mathematics from Villanova University, and has worked in computer-related jobs from Wall Street to the University of Pennsylvania. His hero is Paul Erdos, a brilliant number theorist who was known for his open collaboration with others.

Mike's notes page is souptonuts. For open source consulting needs, please send an email to All consulting work must include a donation to Logo Logo