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;
; Move the nth member of the list to the front. If n is too large, the
; last member is moved. If n is too small, no change. Items are numbered
; from zero. The empy list is returned unchanged.
(defun getnth (n lst)
(cond
((null lst) lst) ; List empty. Return it.
((< n 0) lst) ; n is too small. Return list.
((null (cdr lst)) lst) ; Reached last member of list. Return list.
((= n 0) lst) ; Right thing already at front.
(t
; The nth member of lst is the n-1st member of (cdr lst).
; Move the n-1 st member of (cdr lst) to its front, then
; construct the final result.
(let* ((moverest (getnth (- n 1) (cdr lst))))
(cons (car moverest) (cons (car lst) (cdr moverest))))
)
)
)
;
; Shuffle the list.
(defun shuffle (lst)
(cond
((null lst) lst)
(t
(let*
(
(llen (length lst))
(ranfront (getnth (random llen) lst))
)
(cons (car ranfront) (shuffle (cdr ranfront)))
)
)
)
)