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| -rw-r--r-- | racket.html.markdown | 14 |
1 files changed, 11 insertions, 3 deletions
diff --git a/racket.html.markdown b/racket.html.markdown index 707919dd..84dc2ada 100644 --- a/racket.html.markdown +++ b/racket.html.markdown @@ -404,10 +404,18 @@ vec ; => #(1 2 3 4) ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ; 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! (define-syntax-rule (swap x y) |