/// <summary>
/// Transform an infix expression string into
/// a postfix expression string
/// </summary>
public Stack<string> InfixToPostfix(string expression)
{
var operands = new Stack<Token>();
var postfix = new Stack<Token>();
foreach (Token token in expression.Tokens()) {
if (token.IsEmpty) continue;
switch (token.Class) {
case TokenClass.Name:
case TokenClass.Operand:
#region Test for uniary operator
if (operands.HasItems()
&& operands.Peek().Class == TokenClass.UniaryPrefix) {
switch (operands.Peek().Value) {
case "-":
// turn a uniary minus and operand into a negative operand
operands.Pop();
postfix.Push(token);
postfix.Push(new Token("-1"));
postfix.Push(new Token("*"));
break;
case "+":
// no change to operand, remove uniary
postfix.Push(token);
operands.Pop();
break;
default:
throw new Exception("Unexpected operator");
}
#endregion
} else {
postfix.Push(token);
}
break;
case TokenClass.UniaryPostfix:
operands.Push(token);
break;
case TokenClass.UniaryPrefix:
case TokenClass.Function:
case TokenClass.OpenBracket:
#region Test for uniary operator
if (operands.HasItems()
&& operands.Peek().Class == TokenClass.UniaryPrefix) {
switch (operands.Peek().Value) {
case "-":
// change value, which will get picked up on bracket close
token.Value = "-";
operands.Pop(); // remove uniary
operands.Push(token); // push bracket
break;
case "+":
operands.Pop(); // remove uniary
operands.Push(token); // push bracket
break;
default:
throw new Exception("Unexpected operator");
}
#endregion
} else {
operands.Push(token);
}
break;
case TokenClass.ArgumentSeperator:
while (operands.HasItems()
&& operands.Peek().Class != TokenClass.OpenBracket) {
if (operands.Count < 1) throw new Exception("Argument seperator outside of argument list");
postfix.Push(operands.Pop());
}
break;
case TokenClass.BinaryOperator:
while (operands.HasItems()
&& token.ShouldDisplace(operands.Peek())) { // compare precedence
postfix.Push(operands.Pop());
}
operands.Push(token);
break;
case TokenClass.CloseBracket:
while (operands.HasItems()
&& operands.Peek().Class != TokenClass.OpenBracket) { // add inner bracket contents
postfix.Push(operands.Pop());
}
#region Check for previously caught uniary minus bracket "-(...)"
if (operands.HasItems()) {
Token ob = operands.Pop(); // check open bracket
if (ob.Value == "-") { // invert value
postfix.Push(new Token("-1"));
postfix.Push(new Token("*"));
}
}
#endregion
if (operands.HasItems()
&& operands.Peek().Class == TokenClass.Function) {// this is actually a function
postfix.Push(operands.Pop());
}
break;
default:
throw new Exception("Unexpected token: " + token.Value);
} // end of switch
} // end of token stream
// deal with any remaining operators
while (operands.HasItems()) { // compare precedence
postfix.Push(operands.Pop());
}
var output = new Stack<string>(postfix.Count);
foreach (Token t in postfix) output.Push(t.Value.Trim());
return output;
}
