public ParseNode(ParseToken Token)
{
if (Token.type == TokenType.SYMBOL)
{
Value = TruthValue.Unknown;
}
else
{
Value = null;
}
this.Token = Token;
Left = null;
Right = null;
}
/// <summary>
/// Given the string of original input, a list of Parse Tokens, and the
/// target offender, find the index the token begins and the length of the
/// token.
/// </summary>
/// <param name="Input">Original infix input. </param>
/// <param name="List">Sequence of infix tokens. </param>
/// <param name="Target">Token to find the start index and length of</param>
/// <param name="Start">0 based index in Input were Target begins.</param>
/// <param name="Length">Length of target in characters. </param>
/// <returns></returns>
private static bool FindToken(string Input, List <ParseToken> List, ParseToken Target,
out int Start, out int Length)
{
int cur_ind = 0;
foreach (ParseToken pt in List)
{
cur_ind = Input.IndexOf(pt.symbol, cur_ind);
if (pt == Target)
{
break;
}
}
Start = cur_ind;
Length = Target.symbol.Length;
return(true);
}
/// <summary>
/// Break down a string of space delmited input into parse tokens. If a token
/// does not follow syntax, a FormatException will be thrown.
/// </summary>
/// <param name="input">Space delimited input</param>
/// <returns></returns>
private static List <ParseToken> Tokenize(string input)
{
List <ParseToken> result = new List <ParseToken>();
string[] toks = input.Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
foreach (string t in toks)
{
try
{
result.Add(ParseToken.Parse(t));
}
catch (ArgumentException)
{
throw new FormatException(string.Format("{0} is not a valid operator or symbol.", t));
}
}
return(result);
}
/// <summary>
/// Attempt to parse an RPN sequence of Parse tokens. If successful return the reslting
/// tree, else return null and populate the Error and ErrorMessage parameters.
/// </summary>
/// <param name="Input">RPN sequence of Tokens. </param>
/// <param name="Error">Container for Token of Error</param>
/// <param name="ErrorMessage">Error message regarding violating token. </param>
/// <returns>A binary expression tree if succesful, otherwise null. </returns>
public static ParseTree Parse(List <ParseToken> Input, out ParseToken Error, out string ErrorMessage)
{
Dictionary <string, List <ParseNode> > symbolTable = new Dictionary <string, List <ParseNode> >();
Stack <ParseNode> wSet = new Stack <ParseNode>(); //Stack for processing.
ParseNode c;
foreach (ParseToken pt in Input)
{
try
{
c = new ParseNode(pt);
if (c.IsOperator)
{
//NOT is the only operator that requires
//a single operand.
if (c.Operation == Operation.NOT)
{
c.Left = wSet.Pop();
}
else
{
//Right was placed on the stack last
//This order does not matter except for IF operators
c.Right = wSet.Pop();
c.Left = wSet.Pop();
}
//and push it on the stack (fall through)
}
else
{
//if its an operand we want to add it to our symbol table.
try
{
symbolTable.Add(c.Token.symbol, new List <ParseNode>()
{
c
});
}
catch (ArgumentException)
{
symbolTable[c.Token.symbol].Add(c);
} //Thrown when the key is already present, so at it to the current list.
}
wSet.Push(c);
}
catch (InvalidOperationException)
{
//An operator was not able to pop its needed
//operands from the working set.
Error = pt;
ErrorMessage = string.Format("Too few operands for {0}.", pt.symbol);
return(null);
}
}
if (wSet.Count == 0)
{
//We lost out root?
throw new Exception();
}
if (wSet.Count > 1)
{
//If there are still things in the wSet more than
//one thing left in the stack there was too many
//operands for the operators.
while (wSet.Peek().IsOperator&& wSet.Count > 1)
{
wSet.Pop();
}
Error = wSet.Peek().Token;
ErrorMessage = string.Format(
"Unused operands starting w/ {0}.", wSet.Peek().Token.symbol);
return(null);
}
Error = null;
ErrorMessage = null;
return(new ParseTree(wSet.Pop(), symbolTable));
}
