一応CLISPとも比較
GNU CLISP 2.29 (-Cオプション)

(defmacro nest (N nest-level &body body)
(if (<= nest-level 1)
`(loop repeat ,N do ,@body)
`(loop repeat ,N do (nest ,N ,(1- nest-level) ,@body))))

(defun test (&aux (x 0))
(nest 16 6 (incf x))
(print x))

(test)

=> 0.13 / ruby 1.8.1 (2003-12-25) [powerpc-darwin]