A ShuntingYard consisting of two structures: a queue of values and a stack of operators.
NOTE: apparently, this is never used!
Value parameters
operators
a stack of operators which is temporarily placed here until switch is called.
values
a list of values and operators. The former are added directly to values. However, operators are only added indirectly, after a closing parenthesis (or the end of the string) is reached.
a new ShuntingYard which is the same as this but with token added. If token is an operator, it is added to the operators; If token is a number, it is added to the values; If token is a open or close parenthesis, it is handled specially.