SchemeでClassとProtocol

# ClassとProtocol ---------------------- [Lisp Meet Up presented by Shibuya.lisp #46](https://lisp.connpass.com/event/45517/) Scheme回 <!-- .slide: class="center" --> === # About Me ---------  <!-- .element: style="position:absolute;right:0;z-index:-1" --> * κeen * [@blackenedgold](https://twitter.com/blackenedgold) * Github: [KeenS](https://github.com/KeenS) * サイバーエージェントのエンジニア * Lisp, ML, Rust, Shell Scriptあたりを書きます === # Class ------- * ここでは単に値の集合を表わす * `new` のように新しいインスタンスを作る機能はつけない * ほとんど型と同じ機能 * 唯一の機能 `instance?` を持つ === ``` scheme (instance? 3 <number>) ; => #t (instance? "foo" <number>) ; => #f ``` === # Classの実装 ------------- * 事実上述語があればいい * [詳細](https://github.com/picrin-scheme/picrin/blob/master/contrib/50.class/piclib/picrin/class.scm) ``` scheme (define-class <any> (lambda (x) #t)) (define-class <list> list?) (define-class <procedure> procedure?) (define-class <number> number?) ``` === # Classの用途 ------------- * 述語だけで意味ある？ + プリミティブにのみあった述語をユーザが拡張出来る * その上に何かを構築出来る * protocolとか === # Protocol ----------- * Clojureのprotocol * 多重ディスパッチの機構 * ディスパッチするのにClassを使う === ```scheme (define-protocol (PLUS x y) (plus x y)) (define-instance (PLUS <number> <number>) (lambda (x y) (+ x y))) (define-instance (PLUS <number> <string>) (lambda (x y) (string-append (number->string x) y))) (define-instance (PLUS <string> <string>) (lambda (x y) (string-append x y))) ``` === ``` scheme (display (plus 1 2)) (newline) ; -> 3 (display (plus 1 "foo")) (newline) ; -> 1foo (display (plus "bar" "foo")) (newline) ; -> barfoo (display (plus "bar" 1)) (newline) ; -> "error: method not found" ``` === # ユーザ定義型とProtocol ------------------------ ``` scheme (define-record-type complex (make-complex real img) complex? (real complex-real) (img complex-img)) (define (complex-+ c1 c2) (make-complex (+ (complex-real c1) (complex-real c2)) (+ (complex-img c1) (complex-img c2)))) (define (complex->string c) (string-append (number->string (complex-real c)) "+" (number->string (complex-img c)) "i")) ``` === ```scheme (define-class <complex> complex?) (define-instance (PLUS <complex> <complex>) complex-+) (display (complex->string (plus (make-complex 1 2) (make-complex 2 3)))) (newline) ; -> 3+5i ``` === # Protocolの実装 ---------------- * メソッドの登録とか述語でディスパッチとか割と面倒 * [詳細](https://github.com/picrin-scheme/picrin/blob/master/contrib/80.protocol/piclib/picrin/protocol.scm) === # まとめ --------- * 「追加可能な型」は便利だよ * 型相当のものがあればダイナミックディスパッチ出来るよ * picrinに実装されてるよ `(picrin class)` `(picrin protocol)`