private ExpressionToken ParseExpression(ExpressionToken lhs, TokenPriority priority)
{
while (true)
{
if (lhs.Type == TokenType.MinusOperator)
{
lhs = ParseExpression(UpcomingToken, TokenPriority.UnaryMinus);
if (lhs is ValueToken)
{
lhs = -lhs;
}
else
{
throw new ArgumentException($"Unary minus is valid only for ValueToken!{lhs} is not a ValueToken");
}
NextToken();
break;
}
else if (lhs.Type == TokenType.NotOperator)
{
lhs = ParseExpression(UpcomingToken, TokenPriority.Not);
if (lhs is ValueToken)
{
lhs = !lhs;
}
else
{
throw new ArgumentException($"Unary minus is valid only for ValueToken!{lhs} is not a ValueToken");
}
NextToken();
break;
}
break;
}
while (UpcomingToken is OperatorToken && (UpcomingToken as OperatorToken).Priority >= priority)
{
OperatorToken op = UpcomingToken as OperatorToken;
NextToken();
ExpressionToken rhs = UpcomingToken;
NextToken();
while (UpcomingToken is OperatorToken && (UpcomingToken as OperatorToken).Priority > op.Priority)
{
rhs = ParseExpression(rhs, (UpcomingToken as OperatorToken).Priority);
NextToken();
}
switch (op.Type)
{
case TokenType.PlusOperator:
lhs = lhs + rhs;
break;
case TokenType.MinusOperator:
lhs = lhs - rhs;
break;
case TokenType.DivideOperator:
lhs = lhs / rhs;
break;
case TokenType.MultiplyOperator:
lhs = lhs * rhs;
break;
case TokenType.EqualOperator:
lhs = ExpressionToken.AreTokensEqual(lhs, rhs);
break;
case TokenType.LessOperator:
lhs = lhs < rhs;
break;
case TokenType.GreaterOperator:
lhs = lhs > rhs;
break;
case TokenType.LessOrEqualOperator:
lhs = lhs <= rhs;
break;
case TokenType.GreaterOrEqualOperator:
lhs = lhs >= rhs;
break;
case TokenType.AndOperator:
lhs = lhs & rhs;
break;
case TokenType.OrOperator:
lhs = lhs | rhs;
break;
}
}
return(lhs);
}
