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(defpackage #:mulk.protocols-examples
(:nicknames #:protocols-examples)
(:use #:cl #:protocols))
(in-package #:mulk.protocols-examples)
(define-protocol printable ()
((print-object * stream))
(:strictness t))
(define-protocol serialisable ()
((serialise * stream))
(:strictness t))
(define-protocol additive ()
((add * *)
(negate *)))
(define-protocol multiplicative ()
((multiply * *)
(invert *)))
(define-protocol field (additive multiplicative) ())
(define-protocol serialisable-field (serialisable field) ())
(defgeneric serialise (x stream))
(defgeneric add (x y))
(defgeneric negate (x))
(defgeneric multiply (x stream))
(defgeneric invert (x))
(defclass a () ())
;; The following should signal five style warnings about missing methods.
(implement-protocols a (serialisable-field))
(defclass b () ())
;; Note the two style warnings signalled by the following.
(implement-protocols b (additive multiplicative serialisable)
(defmethod add ((x b) (y b)))
(defmethod negate ((x b)))
(defmethod multiply ((x b) y)))
(print (conforms-to-p 'b 'additive)) ;=> T
(print (really-conforms-to-p 'b 'additive)) ;=> T
(print (conforms-to-p 'b 'multiplicative)) ;=> T
(print (really-conforms-to-p 'b 'multiplicative)) ;=> NIL
(print (conforms-to-p 'b 'printable)) ;=> NIL
(print (really-conforms-to-p 'b 'printable)) ;=> NIL
;; The following works because PRINT-OBJECT is specialised over T.
(implement-protocols b (printable))
(print (conforms-to-p 'b 'printable)) ;=> T
(print (really-conforms-to-p 'b 'printable)) ;=> T
(print (subtypep 'b 'printable)) ;=> T
(print (subtypep 'b 'additive)) ;=> T
(print (subtypep 'b 'serialisable)) ;=> NIL
;; Protocols by default inherit their direct ancestors' strictness,
;; where NIL is recessive, while T is dominant. In any case, a
;; strictness default can be overridden by providing the :STRICTNESS
;; option explicitely.
(print (subtypep 'a 'field)) ;=> T
(print (subtypep 'a 'serialisable)) ;=> NIL
(print (subtypep 'a 'serialisable-field)) ;=> NIL
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