Question

LISP FUNCTIONS

Imagine you are writing the AI for a simple game that will require an adversarial search.

The state of the game can be represented using a list of 3 elements, such as (B B B). The list representing the game state can contain any combination of 3 values: A, B, or C. It will always have exactly 3 items. (Let's call it the "state list").

With that in mind, write the following LISP functions:

• TERMINAL-TEST - this function takes a state list as it's only argument. If the list contains no B's, it is considered a terminal state and TERMINAL-TEST should return t, nil otherwise.
  
• UTILITY - this function accepts a state list as it's only argument and evaluates the state list. If the list contains all A's, then the function returns 1. If the list contains all C's, then the function returns -1. Any other combination of A's, B's, or C's returns 0.
  
• ACTIONS - this function accepts a state list as it's only argument and returns a list of possible actions according to the following table:
  

  State	Action
  (B * *)	A1
  (* B *)	A2
  ( * * B)	A3

  
  Where :
  * represents A, B, or C
  State is the state list passed to the function
  Action is the possible action returned given that state
  
  So, if the state list passed to the function was (B C B), then the function should return (A1 A3).
  
• RESULT - this function accepts a state list and an action as it's only arguments. The function then returns a state list according to the following table:
  

  State	Action	Returned
  (B * *)	A1	(A * *)
  (* B *)	A2	(* A *)
  (* * B)	A3	(* * A)

  Where:
  
  State and Action are both passed as arguments and
  Returned is the state list that is returned.
  The * represents A, B, or C.
  
  For example, if (B C B) and A3 were both passed as arguments, then the state list that gets returned would be (B C A).

Demonstrate your functions work by calling each one in turn, passing each of them appropriate arguments, and then printing to the screen the values they returned.

Answer 1

The code, including the test cases is given below, followed by the snapshot.

(defun TERMINAL-TEST (state)
        (and
            (and (not (eq (car state) 'B)) (not (eq (car (cdr state)) 'B) ))
            (not (eq (car (cdr (cdr state))) 'B))
        )
)

(defun UTILITY (state)
    (cond
        ((and
            (and (eq (car state) 'A) (eq (car (cdr state)) 'A) )
            (eq (car (cdr (cdr state))) 'A)
        ) 1 )
        ((and
            (and (eq (car state) 'C) (eq (car (cdr state)) 'C) )
            (eq (car (cdr (cdr state))) 'C)
        ) -1 )
        (T 0)
    )
)

(defun ACTIONS (state)
    (append
        (if (eq (car state) 'B) '(A1) '())
        (if (eq (car (cdr state)) 'B) '(A2) '())
        (if (eq (car (cdr (cdr state))) 'B) '(A3) '())
    )
)

(defun RESULT (state action)
    (cond
        ((and (eq action 'A1) (eq (car state) 'B)) (cons 'A (cdr state)))
        ((and (eq action 'A2) (eq (car (cdr state)) 'B))
            (cons (car state) (cons 'A (cdr (cdr state)))))
        ((and (eq action 'A3) (eq (car (cdr (cdr state))) 'B))
            (cons (car state) (cons (car (cdr state)) '(A))))
        (T state)
    )
)

(write-line "")(format t "(TERMINAL-TEST '(B B B))=~a" (TERMINAL-TEST '(B B B)))
(write-line "")(format t "(TERMINAL-TEST '(A B C))=~a" (TERMINAL-TEST '(A B C)))
(write-line "")(format t "(TERMINAL-TEST '(A C A))=~a" (TERMINAL-TEST '(A C A)))

(write-line "")(format t "(UTILITY '(A A A))=~a" (UTILITY '(A A A)))
(write-line "")(format t "(UTILITY '(C C C))=~a" (UTILITY '(C C C)))
(write-line "")(format t "(UTILITY '(A B C))=~a" (UTILITY '(A B C)))

(write-line "")(format t "(ACTIONS '(B C B))=~a" (ACTIONS '(B C B)))
(write-line "")(format t "(ACTIONS '(B B B))=~a" (ACTIONS '(B B B)))
(write-line "")(format t "(ACTIONS '(A C B))=~a" (ACTIONS '(A C B)))
(write-line "")(format t "(ACTIONS '(A C C))=~a" (ACTIONS '(A C C)))

(write-line "")(format t "(RESULT '(C C C) 'A1)=~a" (RESULT '(C C C) 'A1))
(write-line "")(format t "(RESULT '(B C C) 'A1)=~a" (RESULT '(B C C) 'A1))
(write-line "")(format t "(RESULT '(A B C) 'A2)=~a" (RESULT '(A B C) 'A2))
(write-line "")(format t "(RESULT '(B C B) 'A3)=~a" (RESULT '(B C B) 'A3))
(write-line "")(format t "(RESULT '(B C C) 'A2)=~a" (RESULT '(B C C) 'A2))