klisp-rust/comb at main · kathe/klisp-rust · GitHub

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; (comb n a)    =  N-combinations of set A
; (comb n a t)  =  with repetition

(setq comb
  (lambda (n a . r)
    (labels
      ((tails
         (lambda (a)
           (if (null a)
               nil
               (cons a (tails (cdr a))))))
       (comb
         (lambda (n a)
           (cond
             ((null n) nil)
             ((null (cdr n)) (map list a))
             (else
               (apply conc
                      (map (lambda (tl)
                             (map (lambda (u)
                                    (cons (car tl) u))
                                  (comb (cdr n)
                                        (if r tl (cdr tl)))))
                           (tails a))))))))
      (comb n a))))