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replace unless macro by a while macro

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Manu
2013-07-16 10:51:38 +12:00
parent 13604e7932
commit 6ff708a040
1 changed files with 11 additions and 3 deletions
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racket.html.markdown
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@@ -404,10 +404,18 @@ vec ; => #(1 2 3 4)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Macros let you extend the syntax of the language ; Macros let you extend the syntax of the language
(define-syntax-rule (unless test then else)
(if test else then))
(unless (even? 10) "odd" "even") ; => "even" ; Let's add a while loop
(define-syntax-rule (while condition body ...)
(let loop ()
(when condition
body ...
(loop))))
(let ([i 0])
(while (< i 10)
(displayln i)
(set! i (add1 i))))
; 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)