/// <summary>
/// The shunting yard algorithm that processes a postfix list of expressions/operators.
/// </summary>
/// <param name="context"></param>
/// <param name="parser"></param>
/// <param name="stack"></param>
/// <returns></returns>
public static Expr ProcessShuntingYardList(Context context, Parser.Parser parser, List <object> stack)
{
int index = 0;
Expr finalExp = null;
// Shunting yard algorithm handles POSTFIX operations.
while (index < stack.Count && stack.Count > 0)
{
// Keep moving forward to the first operator * - + / && that is found
// This is a postfix algorithm so it works by creating an expression
// from the last 2 items behind an operator.
if (!(stack[index] is TokenData))
{
index++;
continue;
}
// At this point... we hit an operator
// So get the last 2 items on the stack ( they have to be expressions )
// left is 2 behind current position
// right is 1 behind current position
var left = stack[index - 2] as Expr;
var right = stack[index - 1] as Expr;
TokenData tdata = stack[index] as TokenData;
Token top = tdata.Token;
Operator op = Operators.ToOp(top.Text);
Expr exp = null;
if (Operators.IsMath(op))
{
exp = Exprs.Binary(left, op, right, tdata);
}
else if (Operators.IsConditional(op))
{
exp = Exprs.Condition(left, op, right, tdata);
}
else if (Operators.IsCompare(op))
{
exp = Exprs.Compare(left, op, right, tdata);
}
parser.SetupContext(exp, tdata);
stack.RemoveRange(index - 2, 2);
index = index - 2;
stack[index] = exp;
index++;
}
finalExp = stack[0] as Expr;
return(finalExp);
}