Celestin Apprentice 7/Apprentice-Release7.iso/Environments/PowerLisp 2.01/PowerLisp 2.01 ƒ/Library/clos.lisp

Text File | 1996-05-17 | 61.3 KB | 1,659 lines | [TEXT/ROSA]

;;;-*-Mode:LISP; Package: (CLOSETTE :USE LISP); Base:10; Syntax:Common-lisp -*-
;;;
;;;    Minor modifications for use with PowerLisp 2.0  (May 15, 1996)
;;;
;;; Closette Version 1.0 (February 10, 1991)
;;;
;;; Minor revisions of September 27, 1991 by [e-mail]:
;;;   - remove spurious "&key" in header of initialize-instance method
;;;     for standard-class (bottom of pg.310 of AMOP)
;;;   - add recommendation about not compiling this file
;;;   - change comment to reflect PARC ftp server name change
;;;   - add a BOA constructor to std-instance to please AKCL
;;;   - by default, efunctuate methods rather than compile them
;;;   - also make minor changes to newcl.lisp
;;;
;;; Copyright (c) 1990, 1991 Xerox Corporation.
;;; All rights reserved.
;;;
;;; Use and copying of this software and preparation of derivative works
;;; based upon this software are permitted.  Any distribution of this
;;; software or derivative works must comply with all applicable United
;;; States export control laws.
;;;
;;; This software is made available AS IS, and Xerox Corporation makes no
;;; warranty about the software, its performance or its conformity to any
;;; specification.
;;;
;;;
;;; Closette is an implementation of a subset of CLOS with a metaobject
;;; protocol as described in "The Art of The Metaobject Protocol",
;;; MIT Press, 1991.
;;;
;;; This program is available by anonymous FTP, from the /pub/pcl/mop
;;; directory on parcftp.xerox.com.

;;; This is the file closette.lisp

;;; N.B. Load this source file directly, rather than trying to compile it.

;;(in-package 'closette :use '(lisp))
(provide :clos)
(in-package 'common-lisp)

;;; When running in a Common Lisp that doesn't yet support function names like
;;; (setf foo), you should first load the file newcl.lisp.  This next little
;;; bit imports stuff from there as needed.

#|        ;; RGC
#-Genera
(import '(newcl:print-unreadable-object))

#-Genera
(shadowing-import '(newcl:defun newcl:fboundp newcl:fmakunbound
                    newcl:fdefinition))

#-Genera
(export '(newcl:defun newcl:fboundp newcl:fmakunbound newcl:fdefinition))

#+Genera
(shadowing-import '(future-common-lisp:setf
                    future-common-lisp:fboundp
                    future-common-lisp:fmakunbound
                    future-common-lisp:fdefinition
                    future-common-lisp:print-unreadable-object))

#+Genera
(export '(future-common-lisp:setf
          future-common-lisp:fboundp
          future-common-lisp:fmakunbound
          future-common-lisp:fdefinition
          future-common-lisp:print-unreadable-object))
|#         ;; RGC

(defvar exports
        '(defclass defgeneric defmethod
          find-class class-of
          call-next-method next-method-p
          slot-value slot-boundp slot-exists-p slot-makunbound
          make-instance change-class
          initialize-instance reinitialize-instance shared-initialize
          update-instance-for-different-class
          print-object

          standard-object
          standard-class standard-generic-function standard-method
          class-name

          class-direct-superclasses class-direct-slots
          class-precedence-list class-slots class-direct-subclasses
          class-direct-methods
          generic-function-name generic-function-lambda-list
          generic-function-methods generic-function-discriminating-function
          generic-function-method-class
          method-lambda-list method-qualifiers method-specializers method-body
          method-environment method-generic-function method-function
          slot-definition-name slot-definition-initfunction
          slot-definition-initform slot-definition-initargs
          slot-definition-readers slot-definition-writers
          slot-definition-allocation
          ;;
          ;; Class-related metaobject protocol
          ;;
          compute-class-precedence-list compute-slots
          compute-effective-slot-definition
          finalize-inheritance allocate-instance
          slot-value-using-class slot-boundp-using-class
          slot-exists-p-using-class slot-makunbound-using-class
          ;;
          ;; Generic function related metaobject protocol
          ;;
          compute-discriminating-function
          compute-applicable-methods-using-classes method-more-specific-p
          compute-effective-method-function compute-method-function
          apply-methods apply-method
          describe-object
          find-generic-function  ; Necessary artifact of this implementation
          ))


(export exports)

;;;
;;; Utilities
;;;

;;; push-on-end is like push except it uses the other end:

(defmacro push-on-end (value location)
  `(setf ,location (nconc ,location (list ,value))))

;;; (setf getf*) is like (setf getf) except that it always changes the list,
;;;              which must be non-nil.

(defun (setf getf*) (new-value plist key)
  (block body
    (do ((x plist (cddr x)))
      ((null x))
      (when (eq (car x) key)
        (setf (car (cdr x)) new-value)
        (return-from body new-value)))
    (push-on-end key plist)
    (push-on-end new-value plist)
    new-value))

;;; mapappend is like mapcar except that the results are appended together:

(defun mapappend (fun &rest args)
  (if (some #'null args)
      ()
      (append (apply fun (mapcar #'car args))
              (apply #'mapappend fun (mapcar #'cdr args)))))

;;; mapplist is mapcar for property lists:

(defun mapplist (fun x)
  (if (null x)
      ()
      (cons (funcall fun (car x) (cadr x))
            (mapplist fun (cddr x)))))

;;;
;;; Standard instances
;;;

;;; This implementation uses structures for instances, because they're the only
;;; kind of Lisp object that can be easily made to print whatever way we want.


(defstruct (std-instance (:constructor allocate-std-instance (class slots))
                   #+kcl (:constructor make-std-instance-for-sharp-s)
                         (:predicate std-instance-p)
                         (:print-function print-std-instance))
  class
  slots)

(defun print-std-instance (instance stream depth)
  (declare (ignore depth))
  (print-object instance stream))

;;; Standard instance allocation

(defparameter secret-unbound-value (list "slot unbound"))

(defun instance-slot-p (slot)
  (eq (slot-definition-allocation slot) ':instance))

(defun std-allocate-instance (class)
  (allocate-std-instance
    class
    (allocate-slot-storage (count-if #'instance-slot-p (class-slots class))
                           secret-unbound-value)))

;;; Simple vectors are used for slot storage.

(defun allocate-slot-storage (size initial-value)
  (make-array size :initial-element initial-value))

;;; Standard instance slot access

;;; N.B. The location of the effective-slots slots in the class metaobject for
;;; standard-class must be determined without making any further slot
;;; references.

(defvar the-slots-of-standard-class) ;standard-class's class-slots
(defvar the-class-standard-class)    ;standard-class's class metaobject

(defun slot-location (class slot-name)
  (if (and (eq slot-name 'effective-slots)
           (eq class the-class-standard-class))
      (position 'effective-slots the-slots-of-standard-class
               :key #'slot-definition-name)
      (let ((slot (find slot-name
                        (class-slots class)
                        :key #'slot-definition-name)))
        (if (null slot)
            (error "The slot ~S is missing from the class ~S."
                   slot-name class)
            (let ((pos (position slot
                                 (remove-if-not #'instance-slot-p
                                                (class-slots class)))))
               (if (null pos)
                   (error "The slot ~S is not an instance~@
                           slot in the class ~S."
                          slot-name class)
                   pos))))))

(defun slot-contents (slots location)
  (svref slots location))

(defun (setf slot-contents) (new-value slots location)
  (setf (svref slots location) new-value))

(defun std-slot-value (instance slot-name)
  (let* ((location (slot-location (class-of instance) slot-name))
         (slots (std-instance-slots instance))
         (val (slot-contents slots location)))
    (if (eq secret-unbound-value val)
        (error "The slot ~S is unbound in the object ~S."
               slot-name instance)
        val)))
(defun slot-value (object slot-name)
  (if (eq (class-of (class-of object)) the-class-standard-class)
      (std-slot-value object slot-name)
      (slot-value-using-class (class-of object) object slot-name)))

(defun (setf std-slot-value) (new-value instance slot-name)
  (let ((location (slot-location (class-of instance) slot-name))
        (slots (std-instance-slots instance)))
    (setf (slot-contents slots location) new-value)))
(defun (setf slot-value) (new-value object slot-name)
  (if (eq (class-of (class-of object)) the-class-standard-class)
      (setf (std-slot-value object slot-name) new-value)
      (setf-slot-value-using-class
        new-value (class-of object) object slot-name)))

(defun std-slot-boundp (instance slot-name)
  (let ((location (slot-location (class-of instance) slot-name))
        (slots (std-instance-slots instance)))
    (not (eq secret-unbound-value (slot-contents slots location)))))
(defun slot-boundp (object slot-name)
  (if (eq (class-of (class-of object)) the-class-standard-class)
      (std-slot-boundp object slot-name)
      (slot-boundp-using-class (class-of object) object slot-name)))

(defun std-slot-makunbound (instance slot-name)
  (let ((location (slot-location (class-of instance) slot-name))
        (slots (std-instance-slots instance)))
    (setf (slot-contents slots location) secret-unbound-value))
  instance)
(defun slot-makunbound (object slot-name)
  (if (eq (class-of (class-of object)) the-class-standard-class)
      (std-slot-makunbound object slot-name)
      (slot-makunbound-using-class (class-of object) object slot-name)))

(defun std-slot-exists-p (instance slot-name)
  (not (null (find slot-name (class-slots (class-of instance))
                   :key #'slot-definition-name))))
(defun slot-exists-p (object slot-name)
  (if (eq (class-of (class-of object)) the-class-standard-class)
      (std-slot-exists-p object slot-name)
      (slot-exists-p-using-class (class-of object) object slot-name)))

;;; class-of

(defun class-of (x)
  (if (std-instance-p x)
      (std-instance-class x)
      (built-in-class-of x)))

;;; N.B. This version of built-in-class-of is straightforward but very slow.

(defun built-in-class-of (x)
  (typecase x
    (null                                          (find-class 'null))
    ((and symbol (not null))                       (find-class 'symbol))
    ((complex *)                                   (find-class 'complex))
    ((integer * *)                                 (find-class 'integer))
    ((float * *)                                   (find-class 'float))
    (cons                                          (find-class 'cons))
    (character                                     (find-class 'character))
    (hash-table                                    (find-class 'hash-table))
    (package                                       (find-class 'package))
    (pathname                                      (find-class 'pathname))
    (readtable                                     (find-class 'readtable))
    (stream                                        (find-class 'stream))
    ((and number (not (or integer complex float))) (find-class 'number))
    ((string *)                                    (find-class 'string))
    ((bit-vector *)                                (find-class 'bit-vector))
    ((and (vector * *) (not (or string vector)))   (find-class 'vector))
    ((and (array * *) (not vector))                (find-class 'array))
    ((and sequence (not (or vector list)))         (find-class 'sequence))
    (function                                      (find-class 'function))
    (t                                             (find-class 't))))

;;; subclassp and sub-specializer-p

(defun subclassp (c1 c2)
  (not (null (find c2 (class-precedence-list c1)))))

(defun sub-specializer-p (c1 c2 c-arg)
  (let ((cpl (class-precedence-list c-arg)))
    (not (null (find c2 (cdr (member c1 cpl)))))))

;;;
;;; Class metaobjects and standard-class
;;;

(defparameter the-defclass-standard-class  ;standard-class's defclass form
 '(defclass standard-class ()
      ((name :initarg :name)              ; :accessor class-name
       (direct-superclasses               ; :accessor class-direct-superclasses
        :initarg :direct-superclasses)
       (direct-slots)                     ; :accessor class-direct-slots
       (class-precedence-list)            ; :accessor class-precedence-list
       (effective-slots)                  ; :accessor class-slots
       (direct-subclasses :initform ())   ; :accessor class-direct-subclasses
       (direct-methods :initform ()))))   ; :accessor class-direct-methods

;;; Defining the metaobject slot accessor function as regular functions
;;; greatly simplifies the implementation without removing functionality.

(defun class-name (class) (std-slot-value class 'name))
(defun (setf class-name) (new-value class)
  (setf (slot-value class 'name) new-value))

(defun class-direct-superclasses (class)
  (slot-value class 'direct-superclasses))
(defun (setf class-direct-superclasses) (new-value class)
  (setf (slot-value class 'direct-superclasses) new-value))

(defun class-direct-slots (class)
  (slot-value class 'direct-slots))
(defun (setf class-direct-slots) (new-value class)
  (setf (slot-value class 'direct-slots) new-value))

(defun class-precedence-list (class)
  (slot-value class 'class-precedence-list))
(defun (setf class-precedence-list) (new-value class)
  (setf (slot-value class 'class-precedence-list) new-value))

(defun class-slots (class)
  (slot-value class 'effective-slots))
(defun (setf class-slots) (new-value class)
  (setf (slot-value class 'effective-slots) new-value))

(defun class-direct-subclasses (class)
  (slot-value class 'direct-subclasses))
(defun (setf class-direct-subclasses) (new-value class)
  (setf (slot-value class 'direct-subclasses) new-value))

(defun class-direct-methods (class)
  (slot-value class 'direct-methods))
(defun (setf class-direct-methods) (new-value class)
  (setf (slot-value class 'direct-methods) new-value))

;;; defclass

(defmacro defclass (name direct-superclasses direct-slots
                    &rest options)
  `(ensure-class ',name
     :direct-superclasses
       ,(canonicalize-direct-superclasses direct-superclasses)
     :direct-slots
       ,(canonicalize-direct-slots direct-slots)
     ,@(canonicalize-defclass-options options)))

(defun canonicalize-direct-slots (direct-slots)
   `(list ,@(mapcar #'canonicalize-direct-slot direct-slots)))

(defun canonicalize-direct-slot (spec)
  (if (symbolp spec)
      `(list :name ',spec)
      (let ((name (car spec))
            (initfunction nil)
            (initform nil)
            (initargs ())
            (readers ())
            (writers ())
            (other-options ()))
        (do ((olist (cdr spec) (cddr olist)))
            ((null olist))
          (case (car olist)
            (:initform
             (setq initfunction
                   `(function (lambda () ,(cadr olist))))
             (setq initform `',(cadr olist)))
            (:initarg
             (push-on-end (cadr olist) initargs))
            (:reader
             (push-on-end (cadr olist) readers))
            (:writer
             (push-on-end (cadr olist) writers))
            (:accessor
             (push-on-end (cadr olist) readers)
             (push-on-end `(setf ,(cadr olist)) writers))
            (otherwise
             (push-on-end `',(car olist) other-options)
             (push-on-end `',(cadr olist) other-options))))
        `(list
           :name ',name
           ,@(when initfunction
               `(:initform ,initform
                 :initfunction ,initfunction))
           ,@(when initargs `(:initargs ',initargs))
           ,@(when readers `(:readers ',readers))
           ,@(when writers `(:writers ',writers))
           ,@other-options))))

(defun canonicalize-direct-superclasses (direct-superclasses)
  `(list ,@(mapcar #'canonicalize-direct-superclass direct-superclasses)))

(defun canonicalize-direct-superclass (class-name)
  `(find-class ',class-name))

(defun canonicalize-defclass-options (options)
  (mapappend #'canonicalize-defclass-option options))

(defun canonicalize-defclass-option (option)
  (case (car option)
    (:metaclass
      (list ':metaclass
       `(find-class ',(cadr option))))
    (:default-initargs
      (list
       ':direct-default-initargs
       `(list ,@(mapappend
                  #'(lambda (x) x)
                  (mapplist
                    #'(lambda (key value)
                        `(',key ,value))
                    (cdr option))))))
    (t (list `',(car option) `',(cadr option)))))

;;; find-class

(let ((class-table (make-hash-table :test #'eq)))

  (defun find-class (symbol &optional (errorp t))
    (let ((class (gethash symbol class-table nil)))
      (if (and (null class) errorp)
          (error "No class named ~S." symbol)
          class)))

  (defun (setf find-class) (new-value symbol)
    (setf (gethash symbol class-table) new-value))

  (defun forget-all-classes ()
    (clrhash class-table)
    (values))
 ) ;end let class-table

;;; Ensure class

(defun ensure-class (name &rest all-keys
                          &key (metaclass the-class-standard-class)
                          &allow-other-keys)
  (if (find-class name nil)
      (error "Can't redefine the class named ~S." name)
      (let ((class (apply (if (eq metaclass the-class-standard-class)
                              #'make-instance-standard-class
                              #'make-instance)
                          metaclass :name name all-keys)))
        (setf (find-class name) class)
        class)))

;;; make-instance-standard-class creates and initializes an instance of
;;; standard-class without falling into method lookup.  However, it cannot be
;;; called until standard-class itself exists.

(defun make-instance-standard-class
       (metaclass &key name direct-superclasses direct-slots
                  &allow-other-keys)
  (declare (ignore metaclass))
  (let ((class (std-allocate-instance the-class-standard-class)))
    (setf (class-name class) name)
    (setf (class-direct-subclasses class) ())
    (setf (class-direct-methods class) ())
    (std-after-initialization-for-classes class
       :direct-slots direct-slots
       :direct-superclasses direct-superclasses)
    class))

(defun std-after-initialization-for-classes
       (class &key direct-superclasses direct-slots &allow-other-keys)
  (let ((supers
          (or direct-superclasses
              (list (find-class 'standard-object)))))
    (setf (class-direct-superclasses class) supers)
    (dolist (superclass supers)
      (push class (class-direct-subclasses superclass))))
  (let ((slots
          (mapcar #'(lambda (slot-properties)
                      (apply #'make-direct-slot-definition
                             slot-properties))
                    direct-slots)))
    (setf (class-direct-slots class) slots)
    (dolist (direct-slot slots)
      (dolist (reader (slot-definition-readers direct-slot))
        (add-reader-method
          class reader (slot-definition-name direct-slot)))
      (dolist (writer (slot-definition-writers direct-slot))
        (add-writer-method
          class writer (slot-definition-name direct-slot)))))
  (funcall (if (eq (class-of class) the-class-standard-class)
              #'std-finalize-inheritance
              #'finalize-inheritance)
           class)
  (values))

;;; Slot definition metaobjects

;;; N.B. Quietly retain all unknown slot options (rather than signaling an
;;; error), so that it's easy to add new ones.

(defun make-direct-slot-definition
       (&rest properties
        &key name (initargs ()) (initform nil) (initfunction nil)
             (readers ()) (writers ()) (allocation :instance)
        &allow-other-keys)
  (let ((slot (copy-list properties))) ; Don't want to side effect &rest list
    (setf (getf* slot ':name) name)
    (setf (getf* slot ':initargs) initargs)
    (setf (getf* slot ':initform) initform)
    (setf (getf* slot ':initfunction) initfunction)
    (setf (getf* slot ':readers) readers)
    (setf (getf* slot ':writers) writers)
    (setf (getf* slot ':allocation) allocation)
    slot))

(defun make-effective-slot-definition
       (&rest properties
        &key name (initargs ()) (initform nil) (initfunction nil)
             (allocation :instance)
        &allow-other-keys)
  (let ((slot (copy-list properties)))  ; Don't want to side effect &rest list
    (setf (getf* slot ':name) name)
    (setf (getf* slot ':initargs) initargs)
    (setf (getf* slot ':initform) initform)
    (setf (getf* slot ':initfunction) initfunction)
    (setf (getf* slot ':allocation) allocation)
    slot))

(defun slot-definition-name (slot)
  (getf slot ':name))
(defun (setf slot-definition-name) (new-value slot)
  (setf (getf* slot ':name) new-value))

(defun slot-definition-initfunction (slot)
  (getf slot ':initfunction))
(defun (setf slot-definition-initfunction) (new-value slot)
  (setf (getf* slot ':initfunction) new-value))

(defun slot-definition-initform (slot)
  (getf slot ':initform))
(defun (setf slot-definition-initform) (new-value slot)
  (setf (getf* slot ':initform) new-value))

(defun slot-definition-initargs (slot)
  (getf slot ':initargs))
(defun (setf slot-definition-initargs) (new-value slot)
  (setf (getf* slot ':initargs) new-value))

(defun slot-definition-readers (slot)
  (getf slot ':readers))
(defun (setf slot-definition-readers) (new-value slot)
  (setf (getf* slot ':readers) new-value))

(defun slot-definition-writers (slot)
  (getf slot ':writers))
(defun (setf slot-definition-writers) (new-value slot)
  (setf (getf* slot ':writers) new-value))

(defun slot-definition-allocation (slot)
  (getf slot ':allocation))
(defun (setf slot-definition-allocation) (new-value slot)
  (setf (getf* slot ':allocation) new-value))

;;; finalize-inheritance

(defun std-finalize-inheritance (class)
  (setf (class-precedence-list class)
        (funcall (if (eq (class-of class) the-class-standard-class)
                     #'std-compute-class-precedence-list
                     #'compute-class-precedence-list)
                 class))
  (setf (class-slots class)
        (funcall (if (eq (class-of class) the-class-standard-class)
                     #'std-compute-slots
                     #'compute-slots)
                 class))
  (values))

;;; Class precedence lists

(defun std-compute-class-precedence-list (class)
  (let ((classes-to-order (collect-superclasses* class)))
    (topological-sort classes-to-order
                      (remove-duplicates
                        (mapappend #'local-precedence-ordering
                                   classes-to-order))
                      #'std-tie-breaker-rule)))

;;; topological-sort implements the standard algorithm for topologically
;;; sorting an arbitrary set of elements while honoring the precedence
;;; constraints given by a set of (X,Y) pairs that indicate that element
;;; X must precede element Y.  The tie-breaker procedure is called when it
;;; is necessary to choose from multiple minimal elements; both a list of
;;; candidates and the ordering so far are provided as arguments.

(defun topological-sort (elements constraints tie-breaker)
  (let ((remaining-constraints constraints)
        (remaining-elements elements)
        (result ()))
    (loop
     (let ((minimal-elements
            (remove-if
             #'(lambda (class)
                 (member class remaining-constraints
                         :key #'cadr))
             remaining-elements)))
       (when (null minimal-elements)
             (if (null remaining-elements)
                 (return-from topological-sort result)
               (error "Inconsistent precedence graph.")))
       (let ((choice (if (null (cdr minimal-elements))
                         (car minimal-elements)
                       (funcall tie-breaker
                                minimal-elements
                                result))))
         (setq result (append result (list choice)))
         (setq remaining-elements
               (remove choice remaining-elements))
         (setq remaining-constraints
               (remove choice
                       remaining-constraints
                       :test #'member)))))))

;;; In the event of a tie while topologically sorting class precedence lists,
;;; the CLOS Specification says to "select the one that has a direct subclass
;;; rightmost in the class precedence list computed so far."  The same result
;;; is obtained by inspecting the partially constructed class precedence list
;;; from right to left, looking for the first minimal element to show up among
;;; the direct superclasses of the class precedence list constituent.
;;; (There's a lemma that shows that this rule yields a unique result.)

(defun std-tie-breaker-rule (minimal-elements cpl-so-far)
  (dolist (cpl-constituent (reverse cpl-so-far))
    (let* ((supers (class-direct-superclasses cpl-constituent))
           (common (intersection minimal-elements supers)))
      (when (not (null common))
        (return-from std-tie-breaker-rule (car common))))))

;;; This version of collect-superclasses* isn't bothered by cycles in the class
;;; hierarchy, which sometimes happen by accident.

(defun collect-superclasses* (class)
  (labels ((all-superclasses-loop (seen superclasses)
              (let ((to-be-processed
                       (set-difference superclasses seen)))
                (if (null to-be-processed)
                    superclasses
                    (let ((class-to-process
                             (car to-be-processed)))
                      (all-superclasses-loop
                        (cons class-to-process seen)
                        (union (class-direct-superclasses
                                 class-to-process)
                               superclasses)))))))
    (all-superclasses-loop () (list class))))

;;; The local precedence ordering of a class C with direct superclasses C_1,
;;; C_2, ..., C_n is the set ((C C_1) (C_1 C_2) ...(C_n-1 C_n)).

(defun local-precedence-ordering (class)
  (mapcar #'list
          (cons class
                (butlast (class-direct-superclasses class)))
          (class-direct-superclasses class)))

;;; Slot inheritance

(defun std-compute-slots (class)
  (let* ((all-slots (mapappend #'class-direct-slots
                               (class-precedence-list class)))
         (all-names (remove-duplicates
                      (mapcar #'slot-definition-name all-slots))))
    (mapcar #'(lambda (name)
                (funcall
                  (if (eq (class-of class) the-class-standard-class)
                      #'std-compute-effective-slot-definition
                      #'compute-effective-slot-definition)
                  class
                  (remove name all-slots
                          :key #'slot-definition-name
                          :test-not #'eq)))
            all-names)))

(defun std-compute-effective-slot-definition (class direct-slots)
  (declare (ignore class))
  (let ((initer (find-if-not #'null direct-slots
                             :key #'slot-definition-initfunction)))
    (make-effective-slot-definition
      :name (slot-definition-name (car direct-slots))
      :initform (if initer
                    (slot-definition-initform initer)
                    nil)
      :initfunction (if initer
                        (slot-definition-initfunction initer)
                        nil)
      :initargs (remove-duplicates
                  (mapappend #'slot-definition-initargs
                             direct-slots))
      :allocation (slot-definition-allocation (car direct-slots)))))

;;;
;;; Generic function metaobjects and standard-generic-function
;;;

(defparameter the-defclass-standard-generic-function
 '(defclass standard-generic-function ()
      ((name :initarg :name)      ; :accessor generic-function-name
       (lambda-list               ; :accessor generic-function-lambda-list
          :initarg :lambda-list)
       (methods :initform ())     ; :accessor generic-function-methods
       (method-class              ; :accessor generic-function-method-class
          :initarg :method-class)
       (discriminating-function)  ; :accessor generic-function-
                                  ;    -discriminating-function
       (classes-to-emf-table      ; :accessor classes-to-emf-table
          :initform (make-hash-table :test #'equal)))))

(defvar the-class-standard-gf) ;standard-generic-function's class metaobject

(defun generic-function-name (gf)
  (slot-value gf 'name))
(defun (setf generic-function-name) (new-value gf)
  (setf (slot-value gf 'name) new-value))

(defun generic-function-lambda-list (gf)
  (slot-value gf 'lambda-list))
(defun (setf generic-function-lambda-list) (new-value gf)
  (setf (slot-value gf 'lambda-list) new-value))

(defun generic-function-methods (gf)
  (slot-value gf 'methods))
(defun (setf generic-function-methods) (new-value gf)
  (setf (slot-value gf 'methods) new-value))

(defun generic-function-discriminating-function (gf)
  (slot-value gf 'discriminating-function))
(defun (setf generic-function-discriminating-function) (new-value gf)
  (setf (slot-value gf 'discriminating-function) new-value))

(defun generic-function-method-class (gf)
  (slot-value gf 'method-class))
(defun (setf generic-function-method-class) (new-value gf)
  (setf (slot-value gf 'method-class) new-value))

;;; Internal accessor for effective method function table

(defun classes-to-emf-table (gf)
  (slot-value gf 'classes-to-emf-table))
(defun (setf classes-to-emf-table) (new-value gf)
  (setf (slot-value gf 'classes-to-emf-table) new-value))

;;;
;;; Method metaobjects and standard-method
;;;

(defparameter the-defclass-standard-method
 '(defclass standard-method ()
   ((lambda-list :initarg :lambda-list)     ; :accessor method-lambda-list
    (qualifiers :initarg :qualifiers)       ; :accessor method-qualifiers
    (specializers :initarg :specializers)   ; :accessor method-specializers
    (body :initarg :body)                   ; :accessor method-body
    (environment :initarg :environment)     ; :accessor method-environment
    (generic-function :initform nil)        ; :accessor method-generic-function
    (function))))                           ; :accessor method-function

(defvar the-class-standard-method)    ;standard-method's class metaobject

(defun method-lambda-list (method) (slot-value method 'lambda-list))
(defun (setf method-lambda-list) (new-value method)
  (setf (slot-value method 'lambda-list) new-value))

(defun method-qualifiers (method) (slot-value method 'qualifiers))
(defun (setf method-qualifiers) (new-value method)
  (setf (slot-value method 'qualifiers) new-value))

(defun method-specializers (method) (slot-value method 'specializers))
(defun (setf method-specializers) (new-value method)
  (setf (slot-value method 'specializers) new-value))

(defun method-body (method) (slot-value method 'body))
(defun (setf method-body) (new-value method)
  (setf (slot-value method 'body) new-value))

(defun method-environment (method) (slot-value method 'environment))
(defun (setf method-environment) (new-value method)
  (setf (slot-value method 'environment) new-value))

(defun method-generic-function (method)
  (slot-value method 'generic-function))
(defun (setf method-generic-function) (new-value method)
  (setf (slot-value method 'generic-function) new-value))

(defun method-function (method) (slot-value method 'function))
(defun (setf method-function) (new-value method)
  (setf (slot-value method 'function) new-value))

;;; defgeneric

(defmacro defgeneric (function-name lambda-list &rest options)
  `(ensure-generic-function
     ',function-name
     :lambda-list ',lambda-list
     ,@(canonicalize-defgeneric-options options)))

(defun canonicalize-defgeneric-options (options)
  (mapappend #'canonicalize-defgeneric-option options))

(defun canonicalize-defgeneric-option (option)
  (case (car option)
    (:generic-function-class
      (list ':generic-function-class
            `(find-class ',(cadr option))))
    (:method-class
      (list ':method-class
            `(find-class ',(cadr option))))
    (t (list `',(car option) `',(cadr option)))))

;;; find-generic-function looks up a generic function by name.  It's an
;;; artifact of the fact that our generic function metaobjects can't legally
;;; be stored a symbol's function value.

(let ((generic-function-table (make-hash-table :test #'equal)))

  (defun find-generic-function (symbol &optional (errorp t))
    (let ((gf (gethash symbol generic-function-table nil)))
       (if (and (null gf) errorp)
           (error "No generic function named ~S." symbol)
           gf)))

  (defun (setf find-generic-function) (new-value symbol)
    (setf (gethash symbol generic-function-table) new-value))

  (defun forget-all-generic-functions ()
    (clrhash generic-function-table)
    (values))
 ) ;end let generic-function-table

;;; ensure-generic-function

(defun ensure-generic-function
       (function-name
        &rest all-keys
        &key (generic-function-class the-class-standard-gf)
             (method-class the-class-standard-method)
        &allow-other-keys)
  (if (find-generic-function function-name nil)
      (find-generic-function function-name)
      (let ((gf (apply (if (eq generic-function-class the-class-standard-gf)
                           #'make-instance-standard-generic-function
                           #'make-instance)
                       generic-function-class
                       :name function-name
                       :method-class method-class
                       all-keys)))
         (setf (find-generic-function function-name) gf)
         gf)))

;;; finalize-generic-function

;;; N.B. Same basic idea as finalize-inheritance.  Takes care of recomputing
;;; and storing the discriminating function, and clearing the effective method
;;; function table.

(defun finalize-generic-function (gf)
  (setf (generic-function-discriminating-function gf)
        (funcall (if (eq (class-of gf) the-class-standard-gf)
                     #'std-compute-discriminating-function
                     #'compute-discriminating-function)
                 gf))
  (setf (fdefinition (generic-function-name gf))
        (generic-function-discriminating-function gf))
  (clrhash (classes-to-emf-table gf))
  (values))

;;; make-instance-standard-generic-function creates and initializes an
;;; instance of standard-generic-function without falling into method lookup.
;;; However, it cannot be called until standard-generic-function exists.

(defun make-instance-standard-generic-function
       (generic-function-class &key name lambda-list method-class)
  (declare (ignore generic-function-class))
  (let ((gf (std-allocate-instance the-class-standard-gf)))
    (setf (generic-function-name gf) name)
    (setf (generic-function-lambda-list gf) lambda-list)
    (setf (generic-function-methods gf) ())
    (setf (generic-function-method-class gf) method-class)
    (setf (classes-to-emf-table gf) (make-hash-table :test #'equal))
    (finalize-generic-function gf)
    gf))

;;; defmethod

(defmacro defmethod (&rest args)
  (multiple-value-bind (function-name qualifiers
                        lambda-list specializers body)
        (parse-defmethod args)
    `(ensure-method (find-generic-function ',function-name)
       :lambda-list ',lambda-list
       :qualifiers ',qualifiers
       :specializers ,(canonicalize-specializers specializers)
       :body ',body
       :environment (top-level-environment))))

(defun canonicalize-specializers (specializers)
  `(list ,@(mapcar #'canonicalize-specializer specializers)))

(defun canonicalize-specializer (specializer)
  `(find-class ',specializer))

(defun parse-defmethod (args)
  (let ((fn-spec (car args))
        (qualifiers ())
        (specialized-lambda-list nil)
        (body ())
        (parse-state :qualifiers))
    (dolist (arg (cdr args))
       (ecase parse-state
         (:qualifiers
           (if (and (atom arg) (not (null arg)))
               (push-on-end arg qualifiers)
               (progn (setq specialized-lambda-list arg)
                      (setq parse-state :body))))
         (:body (push-on-end arg body))))
    (values fn-spec
            qualifiers
            (extract-lambda-list specialized-lambda-list)
            (extract-specializers specialized-lambda-list)
            (list* 'block
                   (if (consp fn-spec)
                       (cadr fn-spec)
                       fn-spec)
                   body))))

;;; Several tedious functions for analyzing lambda lists

(defun required-portion (gf args)
  (let ((number-required (length (gf-required-arglist gf))))
    (when (< (length args) number-required)
      (error "Too few arguments to generic function ~S." gf))
    (subseq args 0 number-required)))

(defun gf-required-arglist (gf)
  (let ((plist
          (analyze-lambda-list
            (generic-function-lambda-list gf))))
    (getf plist ':required-args)))

(defun extract-lambda-list (specialized-lambda-list)
  (let* ((plist (analyze-lambda-list specialized-lambda-list))
         (requireds (getf plist ':required-names))
         (rv (getf plist ':rest-var))
         (ks (getf plist ':key-args))
         (aok (getf plist ':allow-other-keys))
         (opts (getf plist ':optional-args))
         (auxs (getf plist ':auxiliary-args)))
    `(,@requireds
      ,@(if rv `(&rest ,rv) ())
      ,@(if (or ks aok) `(&key ,@ks) ())
      ,@(if aok '(&allow-other-keys) ())
      ,@(if opts `(&optional ,@opts) ())
      ,@(if auxs `(&aux ,@auxs) ()))))

(defun extract-specializers (specialized-lambda-list)
  (let ((plist (analyze-lambda-list specialized-lambda-list)))
    (getf plist ':specializers)))

(defun analyze-lambda-list (lambda-list)
  (labels ((make-keyword (symbol)
              (intern (symbol-name symbol)
                      (find-package 'keyword)))
           (get-keyword-from-arg (arg)
              (if (listp arg)
                  (if (listp (car arg))
                      (caar arg)
                      (make-keyword (car arg)))
                  (make-keyword arg))))
    (let ((keys ())           ; Just the keywords
          (key-args ())       ; Keywords argument specs
          (required-names ()) ; Just the variable names
          (required-args ())  ; Variable names & specializers
          (specializers ())   ; Just the specializers
          (rest-var nil)
          (optionals ())
          (auxs ())
          (allow-other-keys nil)
          (state :parsing-required))
      (dolist (arg lambda-list)
        (if (member arg lambda-list-keywords)
          (ecase arg
            (&optional
              (setq state :parsing-optional))
            (&rest
              (setq state :parsing-rest))
            (&key
              (setq state :parsing-key))
            (&allow-other-keys
              (setq allow-other-keys 't))
            (&aux
              (setq state :parsing-aux)))
          (case state
            (:parsing-required
             (push-on-end arg required-args)
             (if (listp arg)
                 (progn (push-on-end (car arg) required-names)
                        (push-on-end (cadr arg) specializers))
                 (progn (push-on-end arg required-names)
                        (push-on-end 't specializers))))
            (:parsing-optional (push-on-end arg optionals))
            (:parsing-rest (setq rest-var arg))
            (:parsing-key
             (push-on-end (get-keyword-from-arg arg) keys)
             (push-on-end arg key-args))
            (:parsing-aux (push-on-end arg auxs)))))
      (list  :required-names required-names
             :required-args required-args
             :specializers specializers
             :rest-var rest-var
             :keywords keys
             :key-args key-args
             :auxiliary-args auxs
             :optional-args optionals
             :allow-other-keys allow-other-keys))))

;;; ensure method

(defun ensure-method (gf &rest all-keys)
  (let ((new-method
           (apply
              (if (eq (generic-function-method-class gf)
                      the-class-standard-method)
                  #'make-instance-standard-method
                  #'make-instance)
              (generic-function-method-class gf)
              all-keys)))
    (add-method gf new-method)
    new-method))

;;; make-instance-standard-method creates and initializes an instance of
;;; standard-method without falling into method lookup.  However, it cannot
;;; be called until standard-method exists.

(defun make-instance-standard-method (method-class
                                      &key lambda-list qualifiers
                                           specializers body environment)
  (declare (ignore method-class))
  (let ((method (std-allocate-instance the-class-standard-method)))
    (setf (method-lambda-list method) lambda-list)
    (setf (method-qualifiers method) qualifiers)
    (setf (method-specializers method) specializers)
    (setf (method-body method) body)
    (setf (method-environment method) environment)
    (setf (method-generic-function method) nil)
    (setf (method-function method)
          (std-compute-method-function method))
    method))

;;; add-method

;;; N.B. This version first removes any existing method on the generic function
;;; with the same qualifiers and specializers.  It's a pain to develop
;;; programs without this feature of full CLOS.

(defun add-method (gf method)
  (let ((old-method
           (find-method gf (method-qualifiers method)
                           (method-specializers method) nil)))
    (when old-method (remove-method gf old-method)))
  (setf (method-generic-function method) gf)
  (push method (generic-function-methods gf))
  (dolist (specializer (method-specializers method))
    (pushnew method (class-direct-methods specializer)))
  (finalize-generic-function gf)
  method)

(defun remove-method (gf method)
  (setf (generic-function-methods gf)
        (remove method (generic-function-methods gf)))
  (setf (method-generic-function method) nil)
  (dolist (class (method-specializers method))
    (setf (class-direct-methods class)
          (remove method (class-direct-methods class))))
  (finalize-generic-function gf)
  method)

(defun find-method (gf qualifiers specializers
                    &optional (errorp t))
  (let ((method
          (find-if #'(lambda (method)
                       (and (equal qualifiers
                                   (method-qualifiers method))
                            (equal specializers
                                   (method-specializers method))))
                   (generic-function-methods gf))))
      (if (and (null method) errorp)
          (error "No such method for ~S." (generic-function-name gf))
          method)))

;;; Reader and write methods

(defun add-reader-method (class fn-name slot-name)
  (ensure-method
    (ensure-generic-function fn-name :lambda-list '(object))
    :lambda-list '(object)
    :qualifiers ()
    :specializers (list class)
    :body `(slot-value object ',slot-name)
    :environment (top-level-environment))
  (values))

(defun add-writer-method (class fn-name slot-name)
  (ensure-method
    (ensure-generic-function
      fn-name :lambda-list '(new-value object))
    :lambda-list '(new-value object)
    :qualifiers ()
    :specializers (list (find-class 't) class)
    :body `(setf (slot-value object ',slot-name)
                 new-value)
    :environment (top-level-environment))
  (values))

;;;
;;; Generic function invocation
;;;

;;; apply-generic-function

(defun apply-generic-function (gf args)
  (apply (generic-function-discriminating-function gf) args))

;;; compute-discriminating-function

(defun std-compute-discriminating-function (gf)
  #'(lambda (&rest args)
      (let* ((classes (mapcar #'class-of
                              (required-portion gf args)))
             (emfun (gethash classes (classes-to-emf-table gf) nil)))
        (if emfun
            (funcall emfun args)
            (slow-method-lookup gf args classes)))))

(defun slow-method-lookup (gf args classes)
  (let* ((applicable-methods
           (compute-applicable-methods-using-classes gf classes))
         (emfun
           (funcall
             (if (eq (class-of gf) the-class-standard-gf)
                 #'std-compute-effective-method-function
                 #'compute-effective-method-function)
             gf applicable-methods)))
    (setf (gethash classes (classes-to-emf-table gf)) emfun)
    (funcall emfun args)))

;;; compute-applicable-methods-using-classes

(defun compute-applicable-methods-using-classes
       (gf required-classes)
  (sort
    (copy-list
      (remove-if-not #'(lambda (method)
                         (every #'subclassp
                                required-classes
                                (method-specializers method)))
                     (generic-function-methods gf)))
    #'(lambda (m1 m2)
        (funcall
          (if (eq (class-of gf) the-class-standard-gf)
              #'std-method-more-specific-p
              #'method-more-specific-p)
          gf m1 m2 required-classes))))

;;; method-more-specific-p

(defun std-method-more-specific-p (gf method1 method2 required-classes)
  (declare (ignore gf))
  (mapc #'(lambda (spec1 spec2 arg-class)
            (unless (eq spec1 spec2)
              (return-from std-method-more-specific-p
                 (sub-specializer-p spec1 spec2 arg-class))))
        (method-specializers method1)
        (method-specializers method2)
        required-classes)
  nil)

;;; apply-methods and compute-effective-method-function

(defun apply-methods (gf args methods)
  (funcall (compute-effective-method-function gf methods)
           args))

(defun primary-method-p (method)
  (null (method-qualifiers method)))
(defun before-method-p (method)
  (equal '(:before) (method-qualifiers method)))
(defun after-method-p (method)
  (equal '(:after) (method-qualifiers method)))
(defun around-method-p (method)
  (equal '(:around) (method-qualifiers method)))

(defun std-compute-effective-method-function (gf methods)
  (let ((primaries (remove-if-not #'primary-method-p methods))
        (around (find-if #'around-method-p methods)))
    (when (null primaries)
      (error "No primary methods for the~@
             generic function ~S." gf))
    (if around
        (let ((next-emfun
                (funcall
                   (if (eq (class-of gf) the-class-standard-gf)
                       #'std-compute-effective-method-function
                       #'compute-effective-method-function)
                   gf (remove around methods))))
          #'(lambda (args)
              (funcall (method-function around) args next-emfun)))
        (let ((next-emfun (compute-primary-emfun (cdr primaries)))
              (befores (remove-if-not #'before-method-p methods))
              (reverse-afters
                (reverse (remove-if-not #'after-method-p methods))))
          #'(lambda (args)
              (dolist (before befores)
                (funcall (method-function before) args nil))
              (multiple-value-prog1
                (funcall (method-function (car primaries)) args next-emfun)
                (dolist (after reverse-afters)
                  (funcall (method-function after) args nil))))))))

;;; compute an effective method function from a list of primary methods:

(defun compute-primary-emfun (methods)
  (if (null methods)
      nil
      (let ((next-emfun (compute-primary-emfun (cdr methods))))
        #'(lambda (args)
            (funcall (method-function (car methods)) args next-emfun)))))

;;; apply-method and compute-method-function

(defun apply-method (method args next-methods)
  (funcall (method-function method)
           args
           (if (null next-methods)
               nil
               (compute-effective-method-function
                 (method-generic-function method) next-methods))))

(defun std-compute-method-function (method)
  (let ((form (method-body method))
        (lambda-list (method-lambda-list method)))
    (compile-in-lexical-environment (method-environment method)
      `(lambda (args next-emfun)
         (flet ((call-next-method (&rest cnm-args)
                  (if (null next-emfun)
                      (error "No next method for the~@
                              generic function ~S."
                             (method-generic-function ',method))
                      (funcall next-emfun (or cnm-args args))))
                (next-method-p ()
                  (not (null next-emfun))))
            (apply #'(lambda ,(kludge-arglist lambda-list)
                       ,form)
                   args))))))

;;; N.B. The function kludge-arglist is used to pave over the differences
;;; between argument keyword compatibility for regular functions versus
;;; generic functions.

(defun kludge-arglist (lambda-list)
  (if (and (member '&key lambda-list)
           (not (member '&allow-other-keys lambda-list)))
      (append lambda-list '(&allow-other-keys))
      (if (and (not (member '&rest lambda-list))
               (not (member '&key lambda-list)))
          (append lambda-list '(&key &allow-other-keys))
          lambda-list)))

;;; Run-time environment hacking (Common Lisp ain't got 'em).

(defun top-level-environment ()
  nil) ; Bogus top level lexical environment

(defvar compile-methods nil)      ; by default, run everything interpreted

(defun compile-in-lexical-environment (env lambda-expr)
  (declare (ignore env))
  (if compile-methods
      (compile nil lambda-expr)
      (eval `(function ,lambda-expr))))

;;;
;;; Bootstrap
;;;

(progn  ; Extends to end-of-file (to avoid printing intermediate results).
;;(format t "Beginning to bootstrap Closette...")
(forget-all-classes)
(forget-all-generic-functions)
;; How to create the class hierarchy in 10 easy steps:
;; 1. Figure out standard-class's slots.
(setq the-slots-of-standard-class
      (mapcar #'(lambda (slotd)
                  (make-effective-slot-definition
                    :name (car slotd)
                    :initargs
                      (let ((a (getf (cdr slotd) ':initarg)))
                        (if a (list a) ()))
                    :initform (getf (cdr slotd) ':initform)
                    :initfunction
                      (let ((a (getf (cdr slotd) ':initform)))
                        (if a #'(lambda () (eval a)) nil))
                    :allocation ':instance))
              (nth 3 the-defclass-standard-class)))
;; 2. Create the standard-class metaobject by hand.
(setq the-class-standard-class
      (allocate-std-instance
         'tba
         (make-array (length the-slots-of-standard-class)
                     :initial-element secret-unbound-value)))
;; 3. Install standard-class's (circular) class-of link.
(setf (std-instance-class the-class-standard-class)
      the-class-standard-class)
;; (It's now okay to use class-... accessor).
;; 4. Fill in standard-class's class-slots.
(setf (class-slots the-class-standard-class) the-slots-of-standard-class)
;; (Skeleton built; it's now okay to call make-instance-standard-class.)
;; 5. Hand build the class t so that it has no direct superclasses.
(setf (find-class 't)
  (let ((class (std-allocate-instance the-class-standard-class)))
    (setf (class-name class) 't)
    (setf (class-direct-subclasses class) ())
    (setf (class-direct-superclasses class) ())
    (setf (class-direct-methods class) ())
    (setf (class-direct-slots class) ())
    (setf (class-precedence-list class) (list class))
    (setf (class-slots class) ())
    class))
;; (It's now okay to define subclasses of t.)
;; 6. Create the other superclass of standard-class (i.e., standard-object).
(defclass standard-object (t) ())
;; 7. Define the full-blown version of standard-class.
(setq the-class-standard-class (eval the-defclass-standard-class))
;; 8. Replace all (3) existing pointers to the skeleton with real one.
(setf (std-instance-class (find-class 't))
      the-class-standard-class)
(setf (std-instance-class (find-class 'standard-object))
      the-class-standard-class)
(setf (std-instance-class the-class-standard-class)
      the-class-standard-class)
;; (Clear sailing from here on in).
;; 9. Define the other built-in classes.
(defclass symbol (t) ())
(defclass sequence (t) ())
(defclass array (t) ())
(defclass number (t) ())
(defclass character (t) ())
(defclass function (t) ())
(defclass hash-table (t) ())
(defclass package (t) ())
(defclass pathname (t) ())
(defclass readtable (t) ())
(defclass stream (t) ())
(defclass list (sequence) ())
(defclass null (symbol list) ())
(defclass cons (list) ())
(defclass vector (array sequence) ())
(defclass bit-vector (vector) ())
(defclass string (vector) ())
(defclass complex (number) ())
(defclass integer (number) ())
(defclass float (number) ())
;; 10. Define the other standard metaobject classes.
(setq the-class-standard-gf (eval the-defclass-standard-generic-function))
(setq the-class-standard-method (eval the-defclass-standard-method))
;; Voila! The class hierarchy is in place.
;;(format t "Class hierarchy created.")
;; (It's now okay to define generic functions and methods.)

(defgeneric print-object (instance stream))
(defmethod print-object ((instance standard-object) stream)
  (print-unreadable-object (instance stream :identity t)
     (format stream "~:(~S~)"
                    (class-name (class-of instance))))
  instance)

;;; Slot access

(defgeneric slot-value-using-class (class instance slot-name))
(defmethod slot-value-using-class
           ((class standard-class) instance slot-name)
  (std-slot-value instance slot-name))

(defgeneric (setf slot-value-using-class) (new-value class instance slot-name))
(defmethod (setf slot-value-using-class)
           (new-value (class standard-class) instance slot-name)
  (setf (std-slot-value instance slot-name) new-value))
;;; N.B. To avoid making a forward reference to a (setf xxx) generic function:
(defun setf-slot-value-using-class (new-value class object slot-name)
  (setf (slot-value-using-class class object slot-name) new-value))

(defgeneric slot-exists-p-using-class (class instance slot-name))
(defmethod slot-exists-p-using-class
           ((class standard-class) instance slot-name)
  (std-slot-exists-p instance slot-name))

(defgeneric slot-boundp-using-class (class instance slot-name))
(defmethod slot-boundp-using-class
           ((class standard-class) instance slot-name)
  (std-slot-boundp instance slot-name))

(defgeneric slot-makunbound-using-class (class instance slot-name))
(defmethod slot-makunbound-using-class
           ((class standard-class) instance slot-name)
  (std-slot-makunbound instance slot-name))

;;; Instance creation and initialization

(defgeneric allocate-instance (class))
(defmethod allocate-instance ((class standard-class))
  (std-allocate-instance class))

(defgeneric make-instance (class &key))
(defmethod make-instance ((class standard-class) &rest initargs)
  (let ((instance (allocate-instance class)))
    (apply #'initialize-instance instance initargs)
    instance))
(defmethod make-instance ((class symbol) &rest initargs)
  (apply #'make-instance (find-class class) initargs))

(defgeneric initialize-instance (instance &key))
(defmethod initialize-instance ((instance standard-object) &rest initargs)
  (apply #'shared-initialize instance t initargs))

(defgeneric reinitialize-instance (instance &key))
(defmethod reinitialize-instance
           ((instance standard-object) &rest initargs)
  (apply #'shared-initialize instance () initargs))

(defgeneric shared-initialize (instance slot-names &key))
(defmethod shared-initialize ((instance standard-object)
                              slot-names &rest all-keys)
  (dolist (slot (class-slots (class-of instance)))
    (let ((slot-name (slot-definition-name slot)))
      (multiple-value-bind (init-key init-value foundp)
            (get-properties
              all-keys (slot-definition-initargs slot))
         (declare (ignore init-key))
         (if foundp
             (setf (slot-value instance slot-name) init-value)
             (when (and (not (slot-boundp instance slot-name))
                        (not (null (slot-definition-initfunction slot)))
                        (or (eq slot-names t)
                            (member slot-name slot-names)))
               (setf (slot-value instance slot-name)
                     (funcall (slot-definition-initfunction slot))))))))
  instance)

;;; change-class

(defgeneric change-class (instance new-class &key))
(defmethod change-class
           ((old-instance standard-object)
            (new-class standard-class)
            &rest initargs)
  (let ((new-instance (allocate-instance new-class)))
    (dolist (slot-name (mapcar #'slot-definition-name
                               (class-slots new-class)))
      (when (and (slot-exists-p old-instance slot-name)
                 (slot-boundp old-instance slot-name))
        (setf (slot-value new-instance slot-name)
              (slot-value old-instance slot-name))))
    (rotatef (std-instance-slots new-instance)
             (std-instance-slots old-instance))
    (rotatef (std-instance-class new-instance)
             (std-instance-class old-instance))
    (apply #'update-instance-for-different-class
           new-instance old-instance initargs)
    old-instance))

(defmethod change-class
           ((instance standard-object) (new-class symbol) &rest initargs)
  (apply #'change-class instance (find-class new-class) initargs))

(defgeneric update-instance-for-different-class (old new &key))
(defmethod update-instance-for-different-class
           ((old standard-object) (new standard-object) &rest initargs)
  (let ((added-slots
          (remove-if #'(lambda (slot-name)
                         (slot-exists-p old slot-name))
                     (mapcar #'slot-definition-name
                             (class-slots (class-of new))))))
    (apply #'shared-initialize new added-slots initargs)))

;;;
;;;  Methods having to do with class metaobjects.
;;;

(defmethod print-object ((class standard-class) stream)
  (print-unreadable-object (class stream :identity t)
    (format stream "~:(~S~) ~S"
            (class-name (class-of class))
            (class-name class)))
  class)

(defmethod initialize-instance :after ((class standard-class) &rest args)
  (apply #'std-after-initialization-for-classes class args))

;;; Finalize inheritance

(defgeneric finalize-inheritance (class))
(defmethod finalize-inheritance ((class standard-class))
  (std-finalize-inheritance class)
  (values))

;;; Class precedence lists

(defgeneric compute-class-precedence-list (class))
(defmethod compute-class-precedence-list ((class standard-class))
  (std-compute-class-precedence-list class))

;;; Slot inheritance

(defgeneric compute-slots (class))
(defmethod compute-slots ((class standard-class))
  (std-compute-slots class))

(defgeneric compute-effective-slot-definition (class direct-slots))
(defmethod compute-effective-slot-definition
           ((class standard-class) direct-slots)
  (std-compute-effective-slot-definition class direct-slots))

;;;
;;; Methods having to do with generic function metaobjects.
;;;

(defmethod print-object ((gf standard-generic-function) stream)
  (print-unreadable-object (gf stream :identity t)
     (format stream "~:(~S~) ~S"
             (class-name (class-of gf))
             (generic-function-name gf)))
  gf)

(defmethod initialize-instance :after ((gf standard-generic-function) &key)
  (finalize-generic-function gf))

;;;
;;; Methods having to do with method metaobjects.
;;;

(defmethod print-object ((method standard-method) stream)
  (print-unreadable-object (method stream :identity t)
     (format stream "~:(~S~) ~S~{ ~S~} ~S"
                    (class-name (class-of method))
                    (generic-function-name
                      (method-generic-function method))
                    (method-qualifiers method)
                    (mapcar #'class-name
                            (method-specializers method))))
  method)

(defmethod initialize-instance :after ((method standard-method) &key)
  (setf (method-function method) (compute-method-function method)))

;;;
;;; Methods having to do with generic function invocation.
;;;

(defgeneric compute-discriminating-function (gf))
(defmethod compute-discriminating-function ((gf standard-generic-function))
  (std-compute-discriminating-function gf))

(defgeneric method-more-specific-p (gf method1 method2 required-classes))
(defmethod method-more-specific-p
           ((gf standard-generic-function) method1 method2 required-classes)
  (std-method-more-specific-p gf method1 method2 required-classes))

(defgeneric compute-effective-method-function (gf methods))
(defmethod compute-effective-method-function
           ((gf standard-generic-function) methods)
  (std-compute-effective-method-function gf methods))

(defgeneric compute-method-function (method))
(defmethod compute-method-function ((method standard-method))
  (std-compute-method-function method))

;;; describe-object is a handy tool for enquiring minds:

(defgeneric describe-object (object stream))
(defmethod describe-object ((object standard-object) stream)
  (format t "A Closette object~
             ~%Printed representation: ~S~
             ~%Class: ~S~
             ~%Structure "
          object
          (class-of object))
  (dolist (sn (mapcar #'slot-definition-name
                      (class-slots (class-of object))))
    (format t "~%    ~S <- ~:[not bound~;~S~]"
            sn
            (slot-boundp object sn)
            (and (slot-boundp object sn)
                 (slot-value object sn))))
  (values))
(defmethod describe-object ((object t) stream)
  (lisp:describe object)
  (values))

;;(format t "~%Closette is a Knights of the Lambda Calculus production.")

(values)) ;end progn