Jotter <2026-03-16 Mon>

(let ((x 3))
  (let ((x 4))
    (print x))
  (print x))

(cons 'a ()) ; => (A)
(append '(a b c) '(d e f)) ; => (A B C D E F)
(cons 'a '(b c d)) ; => (A B C D)
(cons 3 '(4 1 2)) ; => (3 4 1 2)

(max 3 4) ;; => 4
(max 2 5 1 3 6) ;; => 6

;; Find the largest number in a list of numbers.

(defun test-max-numbers ()
  (and (= 3 (max-numbers '(1 2 3)))
       (= 1 (max-numbers '(1 1 1)))
       ;; (= nil (max-numbers ()))
       (= 1 (max-numbers '(1)))
       (= 366 (max-numbers '(-365 0 366 5)))
       (= -365 (max-numbers '(-365 -366)))))

(defun max-numbers (ns)
  "Find the largest number in a list of numbers."
  (cond ((null ns) (error "List can not be empty"))
        ((= 1 (length ns)) (first ns))
        (t (max (first ns)
                (max-numbers (rest ns))))))

(test-max-numbers)

;; Return the list of numbers with elements which are
;; double those of the input list.

(= 3 4)
(= 3 (+ 1 2))

(equal '(a b c) '(a b c))
(equal '(a b c) '(a b c d))

(defun test-doubles ()
  (and (equal () (doubles ()))
       (equal '(2) (doubles '(1)))
       (equal '(2 4 6 8) (doubles '(1 2 3 4)))))

(defun doubles (ns)
  "Return a list of the doubles of the input list of numbers"
  (cond ((null ns) ())
        ((consp ns) (cons (* 2 (first ns))
                          (doubles (rest ns))))))

(test-doubles)