/* File: ch3-02.y (modified from lex & yacc book by John Levine) */

%{
#include <stdio.h>
%}

%token NAME NUMBER
%left '-' '+'
%left '*' '/'
%nonassoc UMINUS

%%

statement:  NAME '=' expression
    |   expression      { printf("= %d\n", $1); }
    ;

expression: 
    expression '+' expression           { $$ = $1 + $3; }
    
    |   expression '-' expression       { $$ = $1 - $3; }
    
    |   expression '*' expression       { $$ = $1 * $3; }
    
    |   expression '/' expression
                {   if($3 == 0)
                        yyerror("divide by zero");
                    else
                        $$ = $1 / $3;
                }
    |   '-' expression %prec UMINUS     { $$ = -$2; }
    
    |   '(' expression ')'              { $$ = $2; }
    
    |   NUMBER                          { $$ = $1; }
    ;
%%

main() {
   yyparse() ;
}