defmacro: fluid-let

• Gauche ユーザリファレンス: 4.6 変数束縛

マクロ

• 独習 Scheme 三週間 Chapter 8 マクロ

ほぼ写経ですが。

	;; fluid-let macro
	(define-macro (my-fluid-let xexe . body)
	(let ((xx (map car xexe))
	(ee (map cadr xexe))
	(old-xx (map (lambda (ig)
	(gensym)) xexe))
	(result (gensym)))
	`(let ,(map (lambda (old-x x)
	`(,old-x ,x)) old-xx xx)
	,@(map (lambda (x e)
	`(set! ,x ,e)) xx ee)
	(let ((,result (begin ,@body)))
	,@(map (lambda (x old-x)
	`(set! ,x ,old-x)) xx old-xx)
	,result))))
	(define x 100)
	(define y 200)
	(define (p)
	(format #t "~a:~a\n" x y))
	(p)
	;; 100:200
	;; #<undef>
	(my-fluid-let ((x 10)
	(y 20))
	(p))
	;; 10:20
	;; #<undef>
	(macroexpand '(my-fluid-let ((x 10)
	(y 20))
	(p)))
	; -> (let ((#0=#:G70 x) (#1=#:G71 y)) (set! x 10) (set! y 20) (let ((#2=#:G72 (begin (p)))) (set! x #0#) (set! y #1#) #2#))
	(display
	(macroexpand '(my-fluid-let ((x 10)
	(y 20))
	(p))))
	; -> (let ((G76 x) (G77 y)) (set! x 10) (set! y 20) (let ((G78 (begin (p)))) (set! x G76) (set! y G77) G78))#<undef>
	;; (let ((G76 x)
	;; (G77 y))
	;; (set! x 10)
	;; (set! y 20)
	;; (let ((G78 (begin (p))))
	;; (set! x G76)
	;; (set! y G77)
	;; G78))

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