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;;; -*- Mode: Lisp; Syntax: Common-Lisp; -*-
;;; Code from Paradigms of Artificial Intelligence Programming
;;; Copyright (c) 1991 Peter Norvig
;;;; File overview.lisp: miscellaneous functions from Overview chapter
(defun tax-bracket (income)
"Determine what percent tax should be paid for this income."
(cond ((< income 10000.00) 0.00)
((< income 30000.00) 0.20)
((< income 50000.00) 0.25)
((< income 70000.00) 0.30)
(t 0.35)))
;;; ==============================
(defstruct player (score 0) (wins 0))
(defun determine-winner (players)
"Increment the WINS for the player with highest score."
(incf (player-wins (first (sort players #'>
:key #'player-score)))))
;;; ==============================
(defun length1 (list)
(let ((len 0)) ; start with LEN=0
(dolist (element list) ; and on each iteration
(incf len)) ; increment LEN by 1
len)) ; and return LEN
;;; ==============================
(defun length1.1 (list) ; alternate version:
(let ((len 0)) ; (not my preference)
(dolist (element list len) ; uses len as result here
(incf len))))
;;; ==============================
(defun length2 (list)
(let ((len 0)) ; start with LEN=0
(mapc #'(lambda (element) ; and on each iteration
(incf len)) ; increment LEN by 1
list)
len)) ; and return LEN
;;; ==============================
(defun length3 (list)
(do ((len 0 (+ len 1)) ; start with LEN=0, increment
(l list (rest l))) ; ... on each iteration
((null l) len))) ; (until the end of the list)
;;; ==============================
(defun length4 (list)
(loop for element in list ; go through each element
count t)) ; counting each one
(defun length5 (list)
(loop for element in list ; go through each element
summing 1)) ; adding 1 each time
(defun length6 (list)
(loop with len = 0 ; start with LEN=0
until (null list) ; and (until end of list)
for element = (pop list) ; on each iteration
do (incf len) ; increment LEN by 1
finally (return len))) ; and return LEN
;;; ==============================
(defun length7 (list)
(count-if #'true list))
(defun true (x) t)
;;; ==============================
(defun length8 (list)
(if (null list)
0
(+ 1 (position-if #'true list :from-end t))))
;;; ==============================
(defun length9 (list)
(if (null list)
0
(+ 1 (length9 (rest list)))))
;;; ==============================
(defun length10 (list)
(length10-aux list 0))
(defun length10-aux (sublist len-so-far)
(if (null sublist)
len-so-far
(length10-aux (rest sublist) (+ 1 len-so-far))))
;;; ==============================
(defun length11 (list &optional (len-so-far 0))
(if (null list)
len-so-far
(length11 (rest list) (+ 1 len-so-far))))
;;; ==============================
(defun length12 (the-list)
(labels
((length13 (list len-so-far)
(if (null list)
len-so-far
(length13 (rest list) (+ 1 len-so-far)))))
(length13 the-list 0)))
;;; ==============================
(defun product (numbers)
"Multiply all the numbers together to compute their product."
(let ((prod 1))
(dolist (n numbers prod)
(if (= n 0)
(RETURN 0)
(setf prod (* n prod))))))
;;; ==============================
(defmacro while (test &rest body)
"Repeat body while test is true."
(list* 'loop
(list 'unless test '(return nil))
body))
;;; ==============================
(defmacro while (test &rest body)
"Repeat body while test is true."
(let ((code '(loop (unless test (return nil)) . body)))
(subst test 'test (subst body 'body code))))
;;; ==============================
(defmacro while (test &rest body)
"Repeat body while test is true."
`(loop (unless ,test (return nil))
,@body))
;;; ==============================
(defun dprint (x)
"Print an expression in dotted pair notation."
(cond ((atom x) (princ x))
(t (princ "(")
(dprint (first x))
(pr-rest (rest x))
(princ ")")
x)))
(defun pr-rest (x)
(princ " . ")
(dprint x))
;;; ==============================
(defun pr-rest (x)
(cond ((null x))
((atom x) (princ " . ") (princ x))
(t (princ " ") (dprint (first x)) (pr-rest (rest x)))))
;;; ==============================
(defun same-shape-tree (a b)
"Are two trees the same except for the leaves?"
(tree-equal a b :test #'true))
(defun true (&rest ignore) t)
;;; ==============================
(defun english->french (words)
(sublis '((are . va) (book . libre) (friend . ami)
(hello . bonjour) (how . comment) (my . mon)
(red . rouge) (you . tu))
words))
;;; ==============================
(defstruct node
name
(yes nil)
(no nil))
(defvar *db*
(make-node :name 'animal
:yes (make-node :name 'mammal)
:no (make-node
:name 'vegetable
:no (make-node :name 'mineral))))
(defun questions (&optional (node *db*))
(format t "~&Is it a ~a? " (node-name node))
(case (read)
((y yes) (if (not (null (node-yes node)))
(questions (node-yes node))
(setf (node-yes node) (give-up))))
((n no) (if (not (null (node-no node)))
(questions (node-no node))
(setf (node-no node) (give-up))))
(it 'aha!)
(t (format t "Reply with YES, NO, or IT if I have guessed it.")
(questions node))))
(defun give-up ()
(format t "~&I give up - what is it? ")
(make-node :name (read)))
;;; ==============================
(defun average (numbers)
(if (null numbers)
(error "Average of the empty list is undefined.")
(/ (reduce #'+ numbers)
(length numbers))))
;;; ==============================
(defun average (numbers)
(if (null numbers)
(progn
(cerror "Use 0 as the average."
"Average of the empty list is undefined.")
0)
(/ (reduce #'+ numbers)
(length numbers))))
;;; ==============================
(defun sqr (x)
"Multiply x by itself."
(check-type x number)
(* x x))
;;; ==============================
(defun sqr (x)
"Multiply x by itself."
(assert (numberp x))
(* x x))
;;; ==============================
(defun sqr (x)
"Multiply x by itself."
(assert (numberp x) (x))
(* x x))
;;; ==============================
(defun eat-porridge (bear)
(assert (< too-cold (temperature (bear-porridge bear)) too-hot)
(bear (bear-porridge bear))
"~a's porridge is not just right: ~a"
bear (hotness (bear-porridge bear)))
(eat (bear-porridge bear)))
;;; ==============================
(defun adder (c)
"Return a function that adds c to its argument."
#'(lambda (x) (+ x c)))
;;; ==============================
(defun bank-account (balance)
"Open a bank account starting with the given balance."
#'(lambda (action amount)
(case action
(deposit (setf balance (+ balance amount)))
(withdraw (setf balance (- balance amount))))))
;;; ==============================
(defun math-quiz (op range n)
"Ask the user a series of math problems."
(dotimes (i n)
(problem (random range) op (random range))))
(defun problem (x op y)
"Ask a math problem, read a reply, and say if it is correct."
(format t "~&How much is ~d ~a ~d?" x op y)
(if (eql (read) (funcall op x y))
(princ "Correct!")
(princ "Sorry, that's not right.")))
;;; ==============================
(defun math-quiz (&optional (op '+) (range 100) (n 10))
"Ask the user a series of math problems."
(dotimes (i n)
(problem (random range) op (random range))))
;;; ==============================
(defun math-quiz (&key (op '+) (range 100) (n 10))
"Ask the user a series of math problems."
(dotimes (i n)
(problem (random range) op (random range))))
;;; ==============================
(defun find-all (item sequence &rest keyword-args
&key (test #'eql) test-not &allow-other-keys)
"Find all those elements of sequence that match item,
according to the keywords. Doesn't alter sequence."
(if test-not
(apply #'remove item sequence
:test-not (complement test-not) keyword-args)
(apply #'remove item sequence
:test (complement test) keyword-args)))
;;; ==============================
(defmacro while2 (test &body body)
"Repeat body while test is true."
`(loop (if (not ,test) (return nil))
. ,body))
;;; ==============================
(defun length14 (list &aux (len 0))
(dolist (element list len)
(incf len)))
;;; ==============================
(defun length-r (list)
(reduce #'+ (mapcar #'(lambda (x) 1) list)))
(defun length-r (list)
(reduce #'(lambda (x y) (+ x 1)) list
:initial-value 0))
(defun length-r (list)
(reduce #'+ list :key #'(lambda (x) 1)))
;;; ==============================
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