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The simplest possible macro
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| (define-syntax unless | |
| (syntax-rules () | |
| [(unless e1 e2 e3) | |
| (if (not e1) e2 e3)] | |
| [(unless e1 e2) | |
| (if (not e1) e2 #f)])) | |
| (unless #t (/ 1 0) (+ 1 2 3 4)) ;; 10 | |
| (unless #t (/ 1 0)) ;; #f |
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