Loading in 5 sec....

(defun play (first second) ;4.18 p. 125 (cond ((equal first 'rock)PowerPoint Presentation

(defun play (first second) ;4.18 p. 125 (cond ((equal first 'rock)

- By
**mareo** - Follow User

- 61 Views
- Uploaded on

Download Presentation
## PowerPoint Slideshow about ' (defun play (first second) ;4.18 p. 125 (cond ((equal first 'rock)' - mareo

**An Image/Link below is provided (as is) to download presentation**

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript

(defun play (first second) ;4.18 p. 125

(cond ((equal first 'rock)

(cond ((equal second 'rock) 'tie)

((equal second 'paper) 'second-wins)

(t 'first-wins)))

((equal first 'paper)

(cond ((equal second 'rock) 'first-wins)

((equal second 'paper) 'tie)

(t 'second-wins)))

((equal first 'scissors)

(cond ((equal second 'rock) 'second-wins)

((equal second 'paper) 'first-wins)

(t 'tie)))))

For each possible

value of first player,

decide based on

second player

Note: This version isn’t robust with respect to inappropriate input

(i.e., something that isn’t rock, paper, scissors)

(cond ((equal first 'rock)

(cond ((equal second 'rock) 'tie)

((equal second 'paper) 'second-wins)

(t 'first-wins)))

((equal first 'paper)

(cond ((equal second 'rock) 'first-wins)

((equal second 'paper) 'tie)

(t 'second-wins)))

((equal first 'scissors)

(cond ((equal second 'rock) 'second-wins)

((equal second 'paper) 'first-wins)

(t 'tie)))))

IF THIS

THEN THIS

ELSEIF THIS

THEN THIS

ELSEIF THIS

THEN THIS

COND – a decision list

(defun play (first second)

(cond ((equal first 'rock)

(cond ((equal second 'rock) 'tie)

((equal second 'paper) 'second-wins)

(t 'first-wins)))

((equal first 'paper)

(cond ((equal second 'rock) 'first-wins)

((equal second 'paper) 'tie)

(t 'second-wins)))

((equal first 'scissors)

(cond ((equal second 'rock) 'second-wins)

((equal second 'paper) 'first-wins)

(t 'tie)))))

COND – a decision list

; nice goal one: simplify -- nice to do for YOUR understanding of solution

(defun play (first second)

(cond ((equal first second) 'tie) ; factor out easily checked common case

((equal first 'rock)

(cond ((equal second 'paper) 'second-wins)

(t 'first-wins))) ; second must be scissors

((equal first 'paper)

(cond ((equal second 'rock) 'first-wins)

(t 'second-wins)))

(t ; first must be scissors

(cond ((equal second 'rock) 'second-wins)

(t 'first-wins)))))

Again – it doesn’t guard against inappropriate input

; and simplify again understanding of solution

(defun play (first second)

(cond ((equal first second) 'tie)

((equal first 'rock)

(cond ((equal second 'paper) 'second-wins)

(t 'first-wins)))

((equal first 'paper)

(cond ((equal second 'rock) 'first-wins)

(t 'second-wins)))

((equal second 'rock) 'second-wins)

(t 'first-wins)))

BTW: Simplest code (given equal functionality) is often not best in terms of

comprehensibility and (even) efficiency

; nice goal two: make robust (and comprehensible) understanding of solution

(defun play (first second)

(cond ((equal first 'rock)

(cond ((equal second 'rock) 'tie)

((equal second 'paper) 'second-wins)

((equal second 'scissors) 'first-wins)

(t (list 'second 'unknown))))

((equal first 'paper)

(cond ((equal second 'rock) 'first-wins)

((equal second 'paper) 'tie)

((equal second 'scissors) 'second-wins)

(t (list 'second 'unknown))))

((equal first 'scissors)

(cond ((equal second 'rock) 'second-wins)

((equal second 'paper) 'first-wins)

((equal second 'scissors) 'tie)

(t (list 'second 'unknown))))

(t (list 'first 'unknown))))

; Other formulations understanding of solution

(defun play (first second)

(if (equal first second) ; IF

'tie ; THEN

(if (equal first 'rock) ; ELSE

(if (equal second 'paper)

'second-wins

'first-wins)

(if (equal first 'paper)

(if (equal second 'rock)

'first-wins

'second-wins)

(if (equal second 'rock)

'second-wins

'first-wins)))))

When I wrote this, it was harder for me to keep track of the explicit nesting

-- much harder than keeping track of the logic in the COND (decision list) format

(defun play (first second) understanding of solution

(cond ((and (equal first 'rock) (equal second 'rock)) 'tie)

((and (equal first 'rock) (equal second 'paper)) 'second-wins)

((and (equal first 'rock) (equal second 'scissors)) 'first-wins)

((and (equal first 'paper) (equal second 'rock)) 'first-wins)

((and (equal first 'paper) (equal second 'paper)) 'tie)

((and (equal first 'paper) (equal second 'scissors)) 'second-wins)

((and (equal first 'scissors) (equal second 'rock)) 'second-wins)

((and (equal first 'scissors) (equal second 'paper)) 'first-wins)

((and (equal first 'scissors) (equal second 'scissors)) 'tie)

(t 'unknown-confuguration)))

Doesn’t factor out common conditions at all – a bit unwieldy, but this minimally

structured decision list might also be something that would be more amenable to

automated construction/revision

;5.6 pp. 151-152 understanding of solution

(defun throw-die () (+ 1 (random 6))) ;a

(defun throw-dice () (list (throw-die) (throw-die))) ;b

; (defun throw-dice () (cons (throw-die) (list (throw-die))))

(defun snake-eyes-p (throw) (equal throw '(1 1))) ;c

(defun boxcars-p (throw) (equal throw '(6 6)))

(defun instant-win-p (throw) ;d

(or (equal (eval (cons '+ throw)) 3) ; code should be stylistically consistent

(equal (apply #'+ throw) 11))) ; to aid comprehensibility. I’m trying to

(defun instant-loss-p (throw) ; illustrate different possibilities

(let ((x (apply #'+ throw)))

(or (< x 4) (= x 12))))

(cond ((snake-eyes-p throw) 'snake-eyes)

((boxcars-p throw) 'boxcars)

(t (apply #'+ throw))))

;

;(defun say-throw (throw)

; (let ((x (apply #'+ throw)))

; (cond ((equal x 2) 'snake-eyes)

; ((equal x 12) 'boxcars)

; (t x))))

Using previously defined functions is often good, as it eliminates redundancy

(in effect defining the same functionality repeatedly), which in turn can guard

against bugs being introduced when a function is changed (you only have to

change one, not many). However, the it can also sometimes result in less

efficient code – example later perhaps

(let* ((throw (throw-dice))

(point (say-throw throw))

(suffix (cond ((instant-win-p throw)

(list point '-- 'you 'win))

((instant-loss-p throw)

(list point '-- 'you 'lose))

(t (list 'your 'point 'is point)))))

(cons 'throw

(cons (car throw)

(cons 'and

(cons (cadr throw)

(cons '-- suffix)))))))

; (let* ((throw (throw-dice))

; (point (say-throw throw))

; (suffix (cond ((instant-win-p throw)

; (list point '-- 'you 'win))

; ((instant-loss-p throw)

; (list point '-- 'you 'lose))

; (t (list 'your 'point 'is point)))))

; (append (list 'throw (car throw) 'and (cadr throw) '--)

; suffix)))

(defun try-for-point (winpoint) ;g

(let* ((throw (throw-dice))

(throwpoint (say-throw throw))

(suffix (cond ((equal throwpoint 7) (list 'you 'lose))

((equal throwpoint winpoint) (list 'you 'win))

(t (list 'throw 'again)))))

(cons 'throw

(cons (car throw)

(cons 'and

(cons (cadr throw)

(cons '--

(cons throwpoint

(cons '--

suffix)))))))))

Download Presentation

Connecting to Server..