Export name TYPE-EXPANDER.
Export name of protocol class ENVIRONMENT.
Let NIL be a possible argument for (SETF MACRO-FUNCTION).
Define protocol class ENVIRONMENT.
Define generic function TYPE-EXPANDER.
Define generic function (SETF TYPE-EXPANDER).
Use protocol class as superclass of simple environment.
Added method for TYPE-EXPANDER.
Added method for (SETF TYPE-EXPANDER).