This document discusses Common Lisp Object System (CLOS) and the Metaobject Protocol (MOP). It provides examples of using CLOS to define classes and generic functions. It also shows how MOP can be used for metaprogramming techniques like singleton classes, object-relational mapping, and specializing on object equality. The document suggests CLOS and MOP are useful for implementing domain-specific languages and techniques like interceptors, validation, and lazy initialization.

1. Meta-objective
Lisp
@dico_leque
2011/02/26 NagoyaRejectKaigi

2. n Common Lisp Object System Metaobject
Protocol
n Gauche Scheme interpreter

3. Lisp
n CLOS -- Common Lisp Object System
n
n ISLISP Object System -- ILOS
n Ruby
n ANSI Common Lisp Lisp

4. CLOS (1)
n
n (define-class <foo> () ((slot1) (slot2)))
n
n (define-class <baz> (<foo> <bar>) ())

5. CLOS (2)
n generic-
function
n
(define-generic foo)
(define-method foo ((x <sequence>) (y <sequence>)) 0)
(define-method foo ((x <sequence>) (y <string>)) 1)
(define-method foo ((x <string>) (y <sequence>)) 2)
(define-method foo ((x <string>) (y <string>)) 3)
(foo '() '()) ; => 0
(foo '() "a") ; => 1
(foo "a" '#()) ; => 2
(foo "a" "b") ; => 3

6. CLOS (3)
n CLOS CLOS
n
n

7. MOP
n Metaobject Protocol
n introspection:
API
n intercessory:
API
n intercessory

8. Metaobjects
n
n <class> <generic> <method>
n
(make <class>) (apply-generic-function <generic>)

9. (1)
n
n <singleton-meta>
make
n (instance-of < >)
n singleton singleton

10. (1)
(define-class <singleton-meta> (<class>)
(%the-singleton-instance)
)
(define-method make ((class <singleton-meta>) . initargs)
...)
(define-method instance-of ((class <singleton-meta>) . initargs)
(apply make class initargs))
(define-class <singleton-mixin> ()
()
:metaclass <singleton-meta>)
from gauche/lib/gauche/mop/singleton.scm

11. (2) O/R
n DB
n <orm> DB

12. (2) O/R
(define-class <orm> (<class>) ())
(define-method compute-slots ((cl <orm>))
(let ((super-slots (next-method)))
(lset-union
(lambda (x y)
(eq? (car x) (car y)))
(map (lambda (name)
`(,name
:init-keyword ,(make-keyword name)
:accessor ,(string->symbol (format "~A-of" name))))
(load-slot-names cl))
super-slots)))
(define-class <foo> () ()
:metaclass <orm>)
※ load-slot-names

13. (3)
n Ruby
n
n (eql 0) 0
n <generic> (eql x)

14. (3)
(define-generic fact
:class <eql-specializable-generic>)
(define-method fact ((n (eql 0)))
1)
(define-method fact ((n <integer>))
(* n (fact (- n 1))))

15. (3)
(define-class <eql-specializer> (<class>)
((object
:getter eql-specializer-object
:init-keyword :eql-specializer-object)))
(define (eql obj)
(make <eql-specializer> :eql-specializer-object obj))
(define-class <eql-specializable-generic> (<generic>) ())
(define-method compute-applicable-methods
((gf <eql-specializable-generic>) args)
...)
(define-method sort-applicable-methods
((gf <eql-specializable-generic>) methods args)
...)
※ 60 http://d.hatena.ne.jp/leque/20110105/p1

16. CLOS / MOP
n
n DB
n
n validator

17. CLOS / MOP
n
n
Pascal Costanza, Charlotte Herzeel, Jorge Vallejos, Theo D’Hondt:
“Filtered dispatch”, Proceedings of the 2008 symposium on Dynamic
languages
n
n before, after, around
n

18. CLOS / MOP
n
n
n lazy initialization
n

19. DSL MOP
n DSL Domain
n

20. n Lisper
DSL
n CLOS MOP