(define-module (combinations)
  #:export (combinations))


(define (combinations lst n)
  "Return N length subsequences of elements from
LST."
  (if (or (null? lst) (zero? n))
      (if (zero? n)'(()) '())
      (let loop ((lst lst) (result '()))
        (if (null? lst)
            result
            (let ((next-lst (cdr lst)))
	      (loop next-lst
                    (append result
                            (map (lambda (combo)
                                   (cons (car lst) combo))
                                 (combinations next-lst
					       (1- n))))))))))