Enumeration recursive de l'Ensemble Puissance

pset.el

;; Un peu de combinatoire:
;; 
;; Definition recursive de l'Ensemble Puissance (powerset)
;; (avec variantes stylistiques)

(setq lexical-binding t)

(defun pset (s)
  (if (null s)
      '(())
    (let* ((subs (pset (cdr s)))
	   (aug (mapcar (lambda (sub)
			  (cons (car s) sub))
			subs)))
      (append aug subs))))

(= (length (pset '(a b c))) 8)

(defun pset-cond (s)
  (cond ((null s) '(()))
	(t (let* ((subs (pset-cond (cdr s)))
		  (augs (mapcar (lambda (sub) (cons (car s) sub)) subs)))
	     (append augs subs)))))

(pset-cond '(a b c))
(= (length (pset-cond '(a b c))) 8)

(defun pset-partial (s)
  (cond ((null s) '(()))
	(t (let* ((subs (pset-partial (cdr s)))
		  (pref (-partial #'cons (car s)))
		  (augm (mapcar pref subs)))
	     (append augm subs)))))

(pset. '(a b c))

(defun pset-flat (s)
  (cond ((null s) '(()))
	(t (let ((pref (-partial #'cons (car s))))
	     (append (mapcar pref subs) (pset-flat (cdr s)))))))