public Parser(SymbolTable symbols, Scanner scanner)
{
_symbols = symbols;
_scanner = scanner;
_lookahead = _scanner.ReadToken();
}
public Scanner(string filename, TextReader source, int tabsize)
{
// set up keyword map to TokenKind
dictPop();
_source = source;
_cursor = new Position(filename, 1, 0); // filename could be "(console)" if doing interactive interpretation
_tabsize = tabsize;
ReadChar(); // fetch initial lookahead character
_nextToken = ScanToken(); // fetch initial lookahead token
}
private Token ReadToken()
{
Token result = _lookahead;
_lookahead = _scanner.ReadToken();
return result;
}
/* ReadToken() scans a new token and returns the current lookahead token. */
public Token ReadToken()
{
Token result = _nextToken;
_nextToken = ScanToken();
return result;
}
private Token ScanToken()
{
Token result = new Token(_cursor);
_text.Length = 0;
char ch = ReadChar();
switch (ch)
{
// discard whitespace
case ' ':
case '\t':
case '\n':
case '\r':
while (char.IsWhiteSpace(_nextChar))
ReadChar();
return ScanToken();
case ';':
result.Kind = TokenKind.Semicolon;
break;
case ':':
if (_nextChar == '=')
{
ReadChar();
result.Kind = TokenKind.Assignment;
break;
}
result.Kind = TokenKind.Colon;
break;
case ',':
result.Kind = TokenKind.Comma;
break;
case '~':
result.Kind = TokenKind.Tilde;
break;
case '(':
result.Kind = TokenKind.LeftParenthesis;
break;
case ')':
result.Kind = TokenKind.RightParenthesis;
break;
case '+':
result.Kind = TokenKind.Plus;
break;
case '-':
result.Kind = TokenKind.Minus;
break;
case '*':
result.Kind = TokenKind.Asterisk;
break;
case '/':
result.Kind = TokenKind.Slash;
break;
case '<':
result.Kind = TokenKind.LessThan;
break;
case '>':
result.Kind = TokenKind.GreaterThan;
break;
case '=':
result.Kind = TokenKind.Equal;
break;
case '\\':
result.Kind = TokenKind.Backslash;
break;
case EOF:
result.Kind = TokenKind.EndOfFile;
break;
case '"':
while (_nextChar != '"')
{
if (_nextChar == '\n')
throw new ScannerError(_cursor, "End of line in string literal");
else if (_nextChar == EOF)
throw new ScannerError(_cursor, "End of file in string literal");
_text.Append(ReadChar());
}
ReadChar(); // skip closing quote
result.Kind = TokenKind.Literal_String;
result.Text = _text.ToString();
break;
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9':
_text.Append(ch);
while (_nextChar >= '0' && _nextChar <= '9')
{
_text.Append(_nextChar);
ReadChar();
}
result.Kind = TokenKind.Literal_Integer;
result.Text = _text.ToString();
break;
default:
if (!Char.IsLetter(ch))
throw new ScannerError(_cursor, "Invalid character");
_text.Append(ch);
while (char.IsLetterOrDigit(_nextChar))
{
_text.Append(_nextChar);
ReadChar();
}
// check if the identifier is a keyword
result.Text = _text.ToString();
if (_keywords.ContainsKey(result.Text))
result.Kind = _keywords[result.Text];
else
result.Kind = TokenKind.Identifier;
break;
}
return result;
}
