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Improve macro definition.

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It's more robust to use `let' to have the macro result in its own new
scope.  (Unrelated to the hygiene point, of course.)
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Eli Barzilay
2013-07-16 01:30:51 -04:00
parent e8f8e2331b
commit d8989c2ae3
1 changed files with 1 additions and 2 deletions
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racket.html.markdown
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@@ -423,8 +423,7 @@ vec ; => #(1 2 3 4)
;; Macros are hygienic, you cannot clobber existing variables! ;; Macros are hygienic, you cannot clobber existing variables!
(define-syntax-rule (swap x y) (define-syntax-rule (swap x y)
(begin (let ([tmp x])
(define tmp x)
(set! x y) (set! x y)
(set! y tmp))) (set! y tmp)))