// parse
private string Parse()
{
foreach (string token in Tokens)
{
if (IsNumber(token))
{
Stack.Push(new Number(token));
}
else if (token == "X")
{
Stack.Push(new Number(token));
}
else if (IsUnary(token))
{
Stack.Push(UnaryExpr.Create(Stack, token));
}
else
{
Stack.Push(BinExpr.Create(Stack, token));
}
}
StringBuilder sb = new StringBuilder();
Stack.Pop().Write(sb);
return(sb.ToString());
}
