%{

#include <stdio.h>
#include <string.h>

int yywrap( );
void yyerror(const char* str);


%}
%token VAL
%token PLUS
%token MINUS
%token DIVIDE
%token TIMES
%token LEFT
%token RIGHT
%token DONE

/* give us more detailed errors */
%error-verbose

%%

/* one expression only followed by a new line */
stmt: expr DONE {return 0;}

/* an expression uses + or - or neither */
expr: expr PLUS term {}
    | expr MINUS term {}
    | term {}

/* an expression uses * or / or neither */
term: term TIMES factor {}
    | term DIVIDE factor {}
    | factor {}

factor: VAL {}
      | LEFT expr RIGHT {}


%%


int yywrap( ) {
  return 1;
}

void yyerror(const char* str) {
  fprintf(stderr, "Compiler error: '%s'.\n", str);
}

int main( ) {
  yyparse( );
  return 0;
}