syntax-rules: bind-variables

• macro.txt

こういうの。

(bind-variables ((a 1)
            (b)
            c
            e
            (d (+ a 3)))
           (list a b c d e))
;; -> (1 #f #f 4 #f)

で、自分なりに書いてはみたものの・・・。かなり苦戦しました。
しかも複雑になってしまって、何が何やら。動いてはいるっぽいものの、これじゃーちょっと・・・。それに何よりダサい。

	;; vind-vars
	;; vind-variables http://web.archive.org/web/20060616054033/home.comcast.net/~prunesquallor/macro.txt
	(define-syntax bind-vars
	(syntax-rules ()
	((_ () body ...)
	(let ()
	body ...))
	((_ ((var init)) body ...)
	(let ((var init))
	body ...))
	((_ ((var1 init1)(var2 init2) ...) body ...)
	(bind-vars ((var1 init1))
	(bind-vars ((var2 init2) ...)
	body ...)))
	((_ ((var1)) body ...)
	(bind-vars ((var1 #f)) body ...))
	((_ ((var1)(var2) ...) body ...)
	(bind-vars ((var1))
	(bind-vars ((var2) ...)
	body ...)))
	((_ ((var1)(var2 init2) ...) body ...)
	(bind-vars ((var1))
	(bind-vars ((var2 init2) ...)
	body ...)))
	((_ (var) body ...)
	(bind-vars ((var))
	body ...))
	((_ (var1 var2 ...) body ...)
	(bind-vars (var1)
	(bind-vars (var2 ...) body ...)))
	((_ (var1 (var2) ...) body ...)
	(bind-vars (var1)
	(bind-vars ((var2) ...) body ...)))
	((_ (var1 (var2 init2) ...) body ...)
	(bind-vars (var1)
	(bind-vars ((var2 init2) ...) body...)))))
	(bind-vars ((a 1)
	(b)
	c
	e
	(d (+ a 3)))
	(list a b c d e))
	;; (1 #f #f 4 #f)
	(let ((a 1))
	(bind-vars ((b)
	c
	e
	(d (+ a 3)))
	(list a b c d e)))
	;; (1 #f #f 4 #f)
	(let ((a 1))
	(let ((b #t))
	(bind-vars (c
	e
	(d (+ a 3)))
	(list a b c d e))))
	;; (1 #t #f 4 #f)
	(bind-vars (a b c d e)
	(list a b c d e))
	;; (#f #f #f #f #f)
	(bind-vars ((a)(b)(c)(d)(e))
	(list a b c d e))
	;; (#f #f #f #f #f)
	(bind-vars (a (b 1)(c 2) d (e))
	(list a b c d e))
	;; (#f 1 2 #f #f)

view raw bind-vars.scm hosted with ❤ by GitHub

お手本はこちら。うーん、だいぶスッキリしていますね。「...」だと、こうは書けないですよね。。場合によってはドット対表現で書いた方がスッキリするんですね。

	;; vind-variables http://web.archive.org/web/20060616054033/home.comcast.net/~prunesquallor/macro.txt
	(define-syntax bind-variables
	(syntax-rules ()
	((bind-variables () form . forms)
	(begin form . forms))
	((bind-variables ((variable value0 value1 . more) . more-bindings) form . forms)
	(syntax-error "bind-variables illegal binding" (variable value0 value1 . more)))
	((bind-variables ((variable value) . more-bindings) form . forms)
	(let ((variable value)) (bind-variables more-bindings form . forms)))
	((bind-variables ((variable) . more-bindings) form . forms)
	(let ((variable #f)) (bind-variables more-bindings form . forms)))
	((bind-variables (variable . more-bindings) form . forms)
	(let ((variable #f)) (bind-variables more-bindings form . forms)))
	((bind-variables bindings form . forms)
	(syntax-error "Bindings must be a list." bindings))))
	(bind-variables ((a 1)
	(b)
	c
	e
	(d (+ a 3)))
	(list a b c d e))
	;; (1 #f #f 4 #f)
	(let ((a 1))
	(bind-variables ((b)
	c
	e
	(d (+ a 3)))
	(list a b c d e)))
	;; (1 #f #f 4 #f)
	(let ((a 1))
	(let ((b #t))
	(bind-variables (c
	e
	(d (+ a 3)))
	(list a b c d e))))
	;; (1 #t #f 4 #f)
	(bind-variables (a b c d e)
	(list a b c d e))
	;; (#f #f #f #f #f)
	(bind-variables ((a)(b)(c)(d)(e))
	(list a b c d e))
	;; (#f #f #f #f #f)
	(bind-variables (a (b 1)(c 2) d (e))
	(list a b c d e))
	;; (#f 1 2 #f #f)

view raw bind-variables.scm hosted with ❤ by GitHub

追記

書けてるー（笑）なるほどー。

• How To Become A Hacker: vallog: syntax-rules: bind-variables

	(define-syntax bind-variables
	(syntax-rules ()
	((_ () form ...)
	(begin form ...))
	;; ここはオリジナルの syntax-error がどんな挙動か分からないので割愛
	;; error で置き換えてみたが、本体に form ... が無い、と怒られた
	;; ((_ ((var val0 val1 ...) ...) form ...)
	;; (error "bind-variables illegal binding" (var val0 val1 ...)))
	((_ ((var val) more-bindings ...) form ...)
	(let ((var val)) (bind-variables (more-bindings ...) form ...)))
	((_ ((var) more-bindings ...) form ...)
	(let ((var #f)) (bind-variables (more-bindings ...) form ...)))
	((_ (var more-bindings ...) form ...)
	;; ここは、本当は上のパターンに差し替えたほうが綺麗かも
	(let ((var #f)) (bind-variables (more-bindings ...) form ...)))
	((_ bindings form ...)
	(error "Bindings must be a list." bindings))
	))
	;; ;; 実行例
	;; > (bind-variables ((a 1)
	;; (b)
	;; c
	;; e
	;; (d (+ a 3)))
	;; (list a b c d e))
	;; (1 #f #f 4 #f)
	;; > (let ((a 1))
	;; (bind-variables ((b)
	;; c
	;; e
	;; (d (+ a 3)))
	;; (list a b c d e)))
	;; (1 #f #f 4 #f)
	;; > (let ((a 1))
	;; (let ((b #t))
	;; (bind-variables (c
	;; e
	;; (d (+ a 3)))
	;; (list a b c d e))))
	;; (1 #t #f 4 #f)
	;; > (bind-variables (a b c d e)
	;; (list a b c d e))
	;; (#f #f #f #f #f)
	;; > (bind-variables ((a) (b) (c) (d) (e))
	;; (list a b c d e))
	;; (#f #f #f #f #f)
	;; > (bind-variables (a (b 1) (c 2) d (e))
	;; (list a b c d e))
	;; (#f 1 2 #f #f)
	;; >

view raw bind-variables.ss hosted with ❤ by GitHub