3.1 Problem: Objects

Design a small model of untyped objects: a language, scoping, an adapted substitution function, and a (standard or regular) reduction system.

Start with the simplification of objects as multi-entry functions:
(define-language Object
  (e ::=
     (object (m (x) e) ...)
     (send e m e))
  (y ::=
  (n ::= number)
  (m ::= variable-not-otherwise-mentioned)
  (x ::= variable-not-otherwise-mentioned))
Sometimes we wish to treat this like a variable and at other times, we want to exclude it from this world. To support this two-faced treatment, the grammar includes the syntactic category of y, which consists of the set x of variables and this.