;;; -*- Mode: Lisp -*-
;;;
;;; Answers to exercises in chapter 1 of Nilsson's Principles of A.I.
;;; Copyright (C) 2021 Gene Michael Stover (gene@acm.org)
;;;
;;; This program is free software: you can redistribute it and/or modify
;;; it under the terms of the GNU General Public License as published by
;;; the Free Software Foundation, either version 3 of the License, or
;;; (at your option) any later version.
;;;
;;; This program is distributed in the hope that it will be useful,
;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with this program.  If not, see <https:;;www.gnu.org/licenses/>.
;;;
;;; Documentation is at http://cybertiggyr.com/nilsson_principles/00readme.html
;;;

(defpackage "NILSON_PRINCIPLES.EX_01_03"
  (:use "COMMON-LISP"))

(in-package "NILSON_PRINCIPLES.EX_01_03")

(defun random-elt (x &aux r)
  (setq r (random (length x)))
  (elt x r))

(defun sentence () (append (dnp) (vp)))

(defun vp () (append (v) (dnp)))

(defun pp () (append (p) (dnp)))

(defun p ()
  (random-elt '(("of") ("from") ("in") ("into") ("by") ("with"))))

(defun v ()
  (random-elt '(("approves")
		("creates")
		("loves")
		("distracts")
		("worries")
		("wonders")
		("fixes")
		("breaks") ("botches")
		("repairs")
		("observes")
		("oversees"))))

(defun dnp ()
  (funcall (random-elt (list (lambda () (append (det) (np)))
			     (lambda () (append (dnp) (pp)))))))

(defun np ()
  (funcall (random-elt (list (lambda () (append (a) (np)))
			     (lambda () (n))))))

(defun a ()
  (random-elt '(("new") ("ancient")
		("red") ("green") ("mauve")
		("feline") ("lionine")
		("stinky") ("aromatic")
		("electric")
		("recreational"))))

(defun n ()
  (random-elt '(("president")
		("company")
		("sale")
		("human")
		("cat")
		("dog")
		("humming bird")
		("brown bear") ("black bear")
		("rocket")
		("couch") ("chaise lounge") ("chair")
		("electric car")
		("computer")
		("android") ("robot"))))

(defun det ()
  (random-elt '(("the") ("this") ("that") ("a") ("any") ("an") ("some"))))

;;; end of file