In LOOPS, classes, class variables, and instance variables can have property lists of name/value pairs along with a value. It's useful for documentation, units, or other metadata. For example, this is the declaration of an instance variable "mass":

(mass 2.0 unit 'kg doc "Mass of a body")

unit, doc are property names followed by values.

LOOPS (Lisp Object-Oriented Programming System) is the object extension of Interlisp.

#interlisp #oop #lisp