private Double Consume_Number()
{
Double value = CurrentToken.Value;
_tokens.MoveNext();
CurrentToken = _tokens.Current;
return(value);
}
private Double Consume_Name()
{
string name = CurrentToken.Name;
_tokens.MoveNext();
CurrentToken = _tokens.Current;
Double val = _nameValueTable[name];
return(val);
}
// Comp ::= Exp
// Comp ::= Exp == Exp
// Exp ::= Term
// Exp ::= Term (+/-) Exp
// Term ::= Fac
// Term ::= Fac (*|/) Term
// Fac ::= Number
// Fac ::= ( Comp )
public Double Parse(string expression)
{
_scanner = new MathExpressionScanner(expression);
_tokens = _scanner.Scan().GetEnumerator();
_tokens.MoveNext();
CurrentToken = _tokens.Current;
Double value = P_Comparison();
return(value);
}
public IEnumerable <MathExpressionToken> Scan()
{
MathExpressionToken returnToken = null;
while (_currentOffset < _expression.Length && returnToken == null)
{
char cur = _expression[_currentOffset++];
if (cur != ' ')
{
if (Char.IsDigit(cur))
{
returnToken = GetNumber();
}
else if (Char.IsLetter(cur) || cur == '_')
{
returnToken = GetName();
}
else if (cur == '+' || cur == '-')
{
returnToken = new MathExpressionToken(MathTokenType.AddOp, cur);
}
else if (cur == '*' || cur == '/')
{
returnToken = new MathExpressionToken(MathTokenType.MultiOp, cur);
}
else if (cur == '(')
{
returnToken = new MathExpressionToken(MathTokenType.Open);
}
else if (cur == ')')
{
returnToken = new MathExpressionToken(MathTokenType.Close);
}
else if (cur == '=' || cur == '!')
{
returnToken = GetCompOp(cur);
}
else
{
throw new InvalidOperationException(String.Format("Invalid Character '{0}'", cur));
}
}
if (returnToken != null)
{
yield return(returnToken);
}
returnToken = null;
}
}
private void Consume_CloseParen()
{
_tokens.MoveNext();
CurrentToken = _tokens.Current;
}
private void Consume_MultiOp()
{
_tokens.MoveNext();
CurrentToken = _tokens.Current;
}
private void Consume_EqualsOp()
{
_tokens.MoveNext();
CurrentToken = _tokens.Current;
}