open-object-lab

Piumarta and Warth's Open Objects in R6RS Scheme.

A Scheme implementation of the object model as described in their paper:

• http://piumarta.com/software/cola/objmodel2.pdf

Demo:

Install Racket.
$ ./run demo.ss

Overview

open-object/main.ss

The basic object model and semantics as described in the paper. Objects at this level are tagged Scheme vectors. Everything above this level is accomplished by (send rcvr op . args).

Send is defined as:

(define (send rcvr op . args)
  (apply (bind rcvr (vtable rcvr) op) rcvr args))

There are a few additional low-level provisions for extension:

• (bind rcvr vt op) Delegates to (send method 'bind rcvr vt op) for methods that are not Scheme procedures to produce a bound procedure.
• (vtable:add-method ...) Invokes (send method 'method-added-to vt op) for methods that are not Scheme procedures.
• (object:vtable value) Returns a vtable given any Scheme value.
• (object? value) Return true if value is a tagged object vector.
• (send obj '_slot offset) Read slot in tagged object vector.
• (send obj '_slot= offset value) Write slot in tagged object vector.
• (send vtable 'name) vtable name for debugging purposes.

open-object/write.ss

Recursive object writer modeled after the Scheme (write) procedure.

open-object/scheme-type.ss

A vtable hierarchy for standard Scheme types. Extends object:vtable with a (cond) on the Scheme type predicates.

open-object/slotted.ss

Basic class-oriented objects with enumerated slots.

open-object/method.ss

Methods that implement super. Reifies the message being sent using the context of the vtable implementing the method.

Uses protocols:

• (send method 'bind rcvr vt op)
• (send method 'method-added-to vt op)