public Evaluator(string polynomial)
{
if (string.IsNullOrWhiteSpace(polynomial))
{
throw new ArgumentException($"{nameof(polynomial)} cannot be null or empty");
}
if (polynomial.StartsWith('-'))
{
polynomial = "0" + polynomial;
}
var inputStream = new AntlrInputStream(polynomial);
var lexer = new PolynomialLexer(inputStream);
var commonTokenStream = new CommonTokenStream(lexer);
var parser = new PolynomialParser(commonTokenStream);
var context = parser.expr();
var visitor = new VisitorImpl();
_expr = visitor.Visit(context);
}
private static (IParseTree tree, string parseErrorMessage) TryParseExpression(string expression)
{
ICharStream stream = CharStreams.fromstring(expression);
PolynomialLexer lexer = new PolynomialLexer(stream);
ITokenStream tokens = new CommonTokenStream(lexer);
PolynomialParser parser = new PolynomialParser(tokens)
{
BuildParseTree = true
};
parser.RemoveErrorListeners();
parser.AddErrorListener(new PolynomialErrorListener());
try
{
var tree = parser.parse();
return(tree, string.Empty);
}
catch (ParseCanceledException pce)
{
return(null, pce.Message);
}
}