Lemon

// Simple calculator grammar for Lemon
%token_type {int}

%left PLUS MINUS.
%left TIMES DIVIDE.

%syntax_error {
  fprintf(stderr,"Syntax error!\n");
}

program ::= expr(A). { printf("Result = %d\n", A); }

expr(A) ::= expr(B) PLUS expr(C). { A = B + C; }
expr(A) ::= expr(B) MINUS 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{
    fprintf(stderr,"divide by zero\n");
  }
}
expr(A) ::= INTEGER(B). { A = B; }