;;; -*- scheme -*-

;;; ----------
;;; Esercizio 1:
(define (duplica l)
  (if (null? l)
      '()
      (cons (car l)
	    (cons (car l)
		  (duplica (cdr l))))))

;;; ----------
;;; Esercizio 2:
(define (fact n)
  (define (fact-aux n acc)
    (if (positive? n)
	(fact-aux (- n 1) (* n acc))
	acc))
  (fact-aux n 1))

;;; ----------
;;; Esercizio 3:
(define (somma-liste l1 l2)
  (cond ((null? l1) l2)
        ((null? l2) l1)
        (else
	 (cons (+ (car l1)
		  (car l2))
	       (somma-liste (cdr l1)
			    (cdr l2))))))

;;; ----------
;;; Esercizio 4:
(define (ncons n x l)
  (if (positive? n)
      (ncons (- n 1) x (cons x l))
      l))

;;; ----------
;;; Esercizio 5:
(define (nuplica n l)
  (if (null? l)
      '()
      (ncons n
	     (car l)
	     (nuplica n (cdr l)))))