public SyntaxToken Lex()
{
if (_position >= _text.Length)
{
return(new SyntaxToken(SyntaxKind.EndOfFileToken, _position, "\0", null));
}
var start = _position;
if (char.IsDigit(Current))
{
while (char.IsDigit(Current))
{
Next();
}
var length = _position - start;
var text = _text.Substring(start, length);
if (!int.TryParse(text, out var value))
{
_diagnostics.ReportInvalidNumber(new TextSpan(start, length), _text, typeof(int));
}
return(new SyntaxToken(SyntaxKind.NumberToken, start, text, value));
}
if (char.IsWhiteSpace(Current))
{
while (char.IsWhiteSpace(Current))
{
Next();
}
var length = _position - start;
var text = _text.Substring(start, length);
return(new SyntaxToken(SyntaxKind.WhitespaceToken, start, text, null));
}
if (char.IsLetter(Current))
{
while (char.IsLetter(Current))
{
Next();
}
var length = _position - start;
var text = _text.Substring(start, length);
var kind = SyntaxFacts.GetKeywordKind(text);
return(new SyntaxToken(kind, start, text, null));
}
switch (Current)
{
case '+':
return(new SyntaxToken(SyntaxKind.PlusToken, _position++, "+", null));
case '-':
return(new SyntaxToken(SyntaxKind.MinusToken, _position++, "-", null));
case '*':
return(new SyntaxToken(SyntaxKind.StarToken, _position++, "*", null));
case '/':
return(new SyntaxToken(SyntaxKind.SlashToken, _position++, "/", null));
case '(':
return(new SyntaxToken(SyntaxKind.OpenParenthesisToken, _position++, "(", null));
case ')':
return(new SyntaxToken(SyntaxKind.CloseParenthesisToken, _position++, ")", null));
case '&':
if (Lookahead == '&')
{
_position += 2;
return(new SyntaxToken(SyntaxKind.AmpersandAmpersandToken, start, "&&", null));
}
break;
case '|':
if (Lookahead == '|')
{
_position += 2;
return(new SyntaxToken(SyntaxKind.PipePipeToken, start, "||", null));
}
break;
case '=':
if (Lookahead == '=')
{
_position += 2;
return(new SyntaxToken(SyntaxKind.EqualsEqualsToken, start, "==", null));
}
else
{
_position += 1;
return(new SyntaxToken(SyntaxKind.EqualsToken, start, "=", null));
}
case '!':
if (Lookahead == '=')
{
_position += 2;
return(new SyntaxToken(SyntaxKind.BangEqualsToken, start, "!=", null));
}
else
{
_position += 1;
return(new SyntaxToken(SyntaxKind.BangToken, start, "!", null));
}
}
_diagnostics.ReportBadToken(_position, Current);
return(new SyntaxToken(SyntaxKind.BadToken, _position++, _text.Substring(_position - 1, 1), null));
}
