syntax-rules: nth-value

• macro.txt

多値を返す手続きから受け取った多値の n 番目を返すマクロ。

	;; nth-value
	;; http://web.archive.org/web/20060616054033/home.comcast.net/~prunesquallor/macro.txt
	(define-syntax nth-value
	(syntax-rules ()
	((_ n values-body)
	(call-with-values
	(lambda () values-body)
	(lambda vals
	(list-ref vals n))))))
	(nth-value 0 (apply values '(a b c d e f g)))
	; -> a
	(nth-value 3 (apply values '(a b c d e f g)))
	; -> d
	(nth-value 10 (apply values '(a b c d e f g)))
	; -> *** ERROR: argument out of range: 10

view raw nth-value.scm hosted with ❤ by GitHub

• Gauche ユーザリファレンス: 6.16 制御