public Token GetNextToken()
{
if(!_currentChar.HasValue)
{
return new Token(Token.EOI);
}
if(Char.IsWhiteSpace(_currentChar.Value))
{
AdvancePos();
return GetNextToken();
}
if(char.IsDigit(_currentChar.Value))
{
StringBuilder buffer = new StringBuilder();
while(_currentChar.HasValue && Char.IsDigit(_currentChar.Value))
{
buffer.Append(_currentChar.Value);
AdvancePos();
}
return new Token(Token.INTEGER, buffer.ToString());
}
Token token = null;
switch(_currentChar.Value)
{
case '+':
token = new Token(Token.ADD);
break;
case '-':
token = new Token(Token.SUBTRACT);
break;
case '/':
token = new Token(Token.DIVIDE);
break;
case '*':
token = new Token(Token.MULTIPLY);
break;
case '(':
token = new Token(Token.LPAREN);
break;
case ')':
token = new Token(Token.RPAREN);
break;
}
if(token != null)
{
token.Source = _currentChar.Value.ToString();
AdvancePos();
return token;
}
else
{
throw new InvalidOperationException($"Unknown character {_currentChar.Value}");
}
}
public void Match(int tokenType)
{
if(_currentToken.Type == tokenType)
{
_currentToken = _lexer.GetNextToken();
}
else
{
throw new ArgumentException($"Invalid token type for this position of the equation. Expected {tokenType} but are parsing {_currentToken.Type}");
}
}
public Token GetNextToken()
{
if(!_currentChar.HasValue)
{
return new Token(TokenType.EOF);
}
if(Char.IsWhiteSpace(_currentChar.Value))
{
AdvanceChar();
return GetNextToken();
}
if(Char.IsDigit(_currentChar.Value))
{
string integerValue = string.Empty;
while(_currentChar.HasValue && Char.IsNumber(_currentChar.Value))
{
integerValue += _currentChar.ToString();
AdvanceChar();
}
return new Token(TokenType.INTEGER, integerValue);
}
Token knownToken = null;
switch(_currentChar)
{
case '+':
knownToken = new Token(TokenType.PLUS, "+");
break;
case '-':
knownToken = new Token(TokenType.MINUS, "-");
break;
case '/':
knownToken = new Token(TokenType.DIVIDE, "/");
break;
case '*':
knownToken = new Token(TokenType.MULTIPLY, "*");
break;
case '(':
knownToken = new Token(TokenType.LPARAM, "(");
break;
case ')':
knownToken = new Token(TokenType.RPARAM, ")");
break;
default:
throw new ArgumentException($"Unable to parse {_currentChar.Value}");
}
AdvanceChar();
return knownToken;
}
public Parser(Lexer lexer)
{
_lexer = lexer;
_currentToken = _lexer.GetNextToken();
}