//------------------------------------------------------------------------------------------------------------
private int evaluatePostfix(string postfix, int lineNumber)
{
Stack <string> expression = new Stack <string>(postfix.Split(' ').Reverse());
Stack <int> operands = new Stack <int>();
Stack <int> temps = new Stack <int>();
int firstTemp = _symbolTable.TempLocation;
while (expression.Count > 0)
{
string working = expression.Pop();
if (Int32.TryParse(working, out int intWorking))
{
// working string is an integer value
operands.Push(_symbolTable.FindConstant(intWorking).Location());
}
else if (Toolbelt.IsValidVariable(working))
{
char workingChar = Convert.ToChar(working);
operands.Push(_symbolTable.FindVariable(Convert.ToInt32(workingChar)).Location());
}
else if (Toolbelt.IsOperator(working))
{
int left, right;
char op = Convert.ToChar(working);
if (operands.Count() >= 2)
{
right = operands.Pop();
left = operands.Pop();
}
else if (operands.Count() == 1 && temps.Count >= 1)
{
right = temps.Pop();
left = operands.Pop();
}
else if (temps.Count >= 2)
{
right = temps.Pop();
left = temps.Pop();
}
else
{
return(-1);
}
// load 'left' from memory
_compiledCode.Add(Word.Build((int)EPC.Code.LOAD, left), _workingLineNumber++);
// perform calculation on 'left'
switch (op)
{
case '+':
_compiledCode.Add(Word.Build((int)EPC.Code.ADD, right), _workingLineNumber++);
break;
case '-':
_compiledCode.Add(Word.Build((int)EPC.Code.SUBTRACT, right), _workingLineNumber++);
break;
case '*':
_compiledCode.Add(Word.Build((int)EPC.Code.MULTIPLY, right), _workingLineNumber++);
break;
case '/':
_compiledCode.Add(Word.Build((int)EPC.Code.DIVIDE, right), _workingLineNumber++);
break;
}
// store result in 'temp'
temps.Push(firstTemp - temps.Count());
if (_symbolTable.HasLocation(temps.Peek()) && _symbolTable.AtLocation(temps.Peek()).IsConst())
{
throw new SystemException($"Cannot override constant value at memory[{temps.Peek()}] -on code line {lineNumber}");
}
_compiledCode.Add(Word.Build((int)EPC.Code.STORE, temps.Peek()), _workingLineNumber++);
}
else
{
return(-1);
}
}
return(temps.Pop());
}