misc:software:Common Lisp:PAIP:2章

演習

前の章より

(defun mappend (fn the-list)
  (apply #'append (mapcar fn the-list)))

演習2.1

(defun generate (phrase)
  "Generate a random sentence or phrase"
  (let ((possible-rewrites (rewrites phrase)))
    (cond ((listp phrase)
           (mappend #'generate phrase))
          (possible-rewrites
           (generate (random-elt possible-rewrites)))
          (t (list phrase)))))

演習2.2

規則のリストが既定のとおりであるならば、解答例のように non-terminal-p の処理を (not (null (...))) と書かなくてもよいだろう。

(defun generate (phrase)
  "Generate a random sentence or phrase"
  (cond ((listp phrase)
         (mappend #'generate phrase))
        ((non-terminal-p phrase)
         (generate (random-elt (rewrites phrase))))
        (t (list phrase))))

(defun non-terminal-p (category)
  (rewrites category))

演習2.3

Xバー理論を利用すればよいだろう。

演習2.4

(defun cross-product (fn xlist ylist)
  (mappend #'(lambda (y)
               (mapcar #'(lambda (x) (funcall fn x y))
                       xlist))
           ylist))

(defun combine-all (xlist ylist)
  (cross-product #'append xlist ylist))

(combine-all '((a) (b)) '((1) (2)))
; => ((A 1) (B 1) (A 2) (B 2))

(cross-product #'+ '(1 2 3) '(10 20 30))
; => (11 12 13 21 22 23 31 32 33)

(cross-product #'list '(a b c d e f g h)
               '(1 2 3 4 5 6 7 8))
; => ((A 1) (B 1) (C 1) (D 1) (E 1) (F 1) (G 1) (H 1) (A 2) (B 2) (C 2) (D 2) (E 2)
; (F 2) (G 2) (H 2) (A 3) (B 3) (C 3) (D 3) (E 3) (F 3) (G 3) (H 3) (A 4) (B 4)
; (C 4) (D 4) (E 4) (F 4) (G 4) (H 4) (A 5) (B 5) (C 5) (D 5) (E 5) (F 5) (G 5)
; (H 5) (A 6) (B 6) (C 6) (D 6) (E 6) (F 6) (G 6) (H 6) (A 7) (B 7) (C 7) (D 7)
; (E 7) (F 7) (G 7) (H 7) (A 8) (B 8) (C 8) (D 8) (E 8) (F 8) (G 8) (H 8))

(defun print-cross-product (fn xlist ylist)
  (mapc #'(lambda (y)
            (print (mapcar #'(lambda (x) (funcall fn x y))
                    xlist)))
        ylist))

(print-cross-product #'+ '(1 2 3) '(10 20 30))
; => 

(print-cross-product #'list '(a b c d e f g h)
               '(1 2 3 4 5 6 7 8))
; =>