private int EvaluateInput(string input)
{
CalculatorLexer lexer = new CalculatorLexer(new AntlrInputStream(input));
lexer.RemoveErrorListeners();
lexer.AddErrorListener(new ThrowingErrorListener <int>());
CalculatorParser parser = new CalculatorParser(new CommonTokenStream(lexer));
parser.RemoveErrorListeners();
parser.AddErrorListener(new ThrowingErrorListener <IToken>());
return(new CalculatorVisitor().Visit(parser.expression()));
}
