defmacro: when, unless

• 独習 Scheme 三週間 Chapter 8 マクロ

実は、マクロについては「プログラミングGauche」をサラッと眺めただけだったりします。

• Gauche ユーザリファレンス: 4.9 準クオート(Quasiquote)

	;; when, unless, macroexpand
	;; http://www.sampou.org/scheme/t-y-scheme/t-y-scheme-Z-H-10.html#node_chap_8
	;; when
	(define-macro my-when
	(lambda (test . branch)
	(list 'if test
	(cons 'begin branch))))
	;; quasiquote, unquote, unquote-splicing
	(define-macro my-when
	(lambda (test . branch)
	`(if ,test
	(begin ,@branch))))
	((lambda (x)
	(my-when (> x 5)
	(display "ok")
	(newline)
	(display x)
	(newline))) 6)
	;; ok
	;; 6
	;; #<undef>
	(macroexpand '((lambda (x)
	(my-when (> x 5)
	(display "ok")
	(newline)
	(display x)
	(newline))) 6))
	; -> ((lambda (x) (my-when (> x 5) (display "ok") (newline) (display x) (newline))) 6)
	;; unless
	(define-macro my-unless
	(lambda (test . branch)
	(list 'if (list 'not test)
	(cons 'begin branch))))
	;; quasiquote, unquote, unquote-splicing
	(define-macro my-unless
	(lambda (test . branch)
	`(if (not ,test)
	(begin ,@branch))))
	((lambda (x)
	(my-unless (> x 5)
	(display "ok")
	(newline)
	(display x)
	(newline))) 3)
	;; ok
	;; 3
	;; #<undef>
	(macroexpand '((lambda (x)
	(my-unless (> x 5)
	(display "ok")
	(newline)
	(display x)
	(newline))) 3))
	; -> ((lambda (x) (my-unless (> x 5) (display "ok") (newline) (display x) (newline))) 3)

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