public void AddExpressionToken(ExpressionToken token)
{
ExpressionTokens.Add(token);
}
public static Expression ParseExpression(string expression)
{
List <ExpressionToken> parsedTokens = new List <ExpressionToken>();
char? parsedOperator = null;
string parsedValue = "";
char? parsedName = null;
for (int index = 0; index < expression.Length; index++)
{
char thisChar = expression[index];
if (thisChar == '+' || thisChar == '-') //plus or minus operator
{
//could denote end of previous Expression token
if (parsedValue.Length > 0 || parsedName != null)
{
parsedTokens.Add(ToExpressionToken(parsedOperator, parsedValue, parsedName));
//reset parse state for next ExpressionToken
parsedOperator = null;
parsedValue = "";
parsedName = null;
}
if (parsedOperator != null)
{
throw new ArgumentException("Cannot have two consecutive operators");
}
else
{
parsedOperator = thisChar;
}
}
else if (thisChar == ' ') //ignore whitespace
{
continue;
}
else if (int.TryParse(thisChar + "", out _))
{
if (parsedName != null)
{
throw new ArgumentException("Cannot have another number after token name");
}
parsedValue += thisChar;
}
else if (ExpressionToken.IsValidName(thisChar))
{
if (parsedName == null)
{
parsedName = thisChar;
}
else
{
throw new ArgumentException("Cannot have token names with multiple characters");
}
}
else
{
throw new ArgumentException($"Didn't understand '{thisChar}'");
}
//if no more characters then need to add final token
if (index == expression.Length - 1)
{
parsedTokens.Add(ToExpressionToken(parsedOperator, parsedValue, parsedName));
}
}
Expression parsedExpression = new Expression();
parsedExpression.AddAllExpressionTokens(parsedTokens);
return(parsedExpression);
}
