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+;;; "object.scm" Macroless Object System
+;;;From: whumeniu@datap.ca (Wade Humeniuk)
+
+;;;Date: February 15, 1994
+
+;; Object Construction:
+;; 0 1 2 3 4
+;; #(object-tag get-method make-method! unmake-method! get-all-methods)
+
+(define object:tag "object")
+
+;;; This might be better done using COMLIST:DELETE-IF.
+(define (object:removeq obj alist)
+ (if (null? alist)
+ alist
+ (if (eq? (caar alist) obj)
+ (cdr alist)
+ (cons (car alist) (object:removeq obj (cdr alist))))))
+
+(define (get-all-methods obj)
+ (if (object? obj)
+ ((vector-ref obj 4))
+ (slib:error "Cannot get methods on non-object: " obj)))
+
+(define (object? obj)
+ (and (vector? obj)
+ (eq? object:tag (vector-ref obj 0))))
+
+(define (make-method! obj generic-method method)
+ (if (object? obj)
+ (if (procedure? method)
+ (begin
+ ((vector-ref obj 2) generic-method method)
+ method)
+ (slib:error "Method must be a procedure: " method))
+ (slib:error "Cannot make method on non-object: " obj)))
+
+(define (get-method obj generic-method)
+ (if (object? obj)
+ ((vector-ref obj 1) generic-method)
+ (slib:error "Cannot get method on non-object: " obj)))
+
+(define (unmake-method! obj generic-method)
+ (if (object? obj)
+ ((vector-ref obj 3) generic-method)
+ (slib:error "Cannot unmake method on non-object: " obj)))
+
+(define (make-predicate! obj generic-predicate)
+ (if (object? obj)
+ ((vector-ref obj 2) generic-predicate (lambda (self) #t))
+ (slib:error "Cannot make predicate on non-object: " obj)))
+
+(define (make-generic-method . exception-procedure)
+ (define generic-method
+ (lambda (obj . operands)
+ (if (object? obj)
+ (let ((object-method ((vector-ref obj 1) generic-method)))
+ (if object-method
+ (apply object-method (cons obj operands))
+ (slib:error "Method not supported: " obj)))
+ (apply exception-procedure (cons obj operands)))))
+
+ (if (not (null? exception-procedure))
+ (if (procedure? (car exception-procedure))
+ (set! exception-procedure (car exception-procedure))
+ (slib:error "Exception Handler Not Procedure:"))
+ (set! exception-procedure
+ (lambda (obj . params)
+ (slib:error "Operation not supported: " obj))))
+ generic-method)
+
+(define (make-generic-predicate)
+ (define generic-predicate
+ (lambda (obj)
+ (if (object? obj)
+ (if ((vector-ref obj 1) generic-predicate)
+ #t
+ #f)
+ #f)))
+ generic-predicate)
+
+(define (make-object . ancestors)
+ (define method-list
+ (apply append (map (lambda (obj) (get-all-methods obj)) ancestors)))
+ (define (make-method! generic-method method)
+ (set! method-list (cons (cons generic-method method) method-list))
+ method)
+ (define (unmake-method! generic-method)
+ (set! method-list (object:removeq generic-method method-list))
+ #t)
+ (define (all-methods) method-list)
+ (define (get-method generic-method)
+ (let ((method-def (assq generic-method method-list)))
+ (if method-def (cdr method-def) #f)))
+ (vector object:tag get-method make-method! unmake-method! all-methods))
+
+