1. Lecture 2-1CS250: Intro to AI/Lisp Intelligent Agents Lecture 3-2 October 14 th, 1999 CS250

2. Lecture 2-1CS250: Intro to AI/Lisp Announcements No class on Thursday (October 7th) Next week –Tuesday, Thursday in class –Wednesday 7-9pm in Maclab

3. Lecture 2-1CS250: Intro to AI/Lisp Assignment 1 Turing’s comments –Skimpy answers –Most support: Continuity of nervous system, consciousness Undecidability and intractability Following instructions –Genes = programs Lisp code

4. Lecture 2-1CS250: Intro to AI/Lisp Answering Lisp Questions Style counts –setf is evil Think it works? Try it out! Grab your functions by the tail

5. Lecture 2-1CS250: Intro to AI/Lisp Intelligent Agents What’s an agent? –Little people in the TV

6. Lecture 2-1CS250: Intro to AI/Lisp (defstructure environment "The world in which agents exist.” ;; A list of the agents in the environment (agents '()) ;; The number of time steps simulated so far (step 0) ;; Stop the simulation after this number (max-steps 1000) ;; Stream to display output on (stream t) ;; Have we run initialize on this environment yet? (initialized nil) ;; Current state of the environment; other subtypes ;; add new slots to hold various state information (state nil) )

7. Lecture 2-1CS250: Intro to AI/Lisp (defstructure agent "Agents take actions (based on percepts and the agent program) and receive a score (based on the performance measure). An agent has a body which can take action, and a program to choose the actions, based on percepts." (program #'nothing); fn: percept -> action (body (make-agent-body)) (score 0) (percept nil) (action nil) (name nil))

8. Lecture 2-1CS250: Intro to AI/Lisp (defun run-environment (env) "Basic environment simulator. It gives each agent its percept, gets an action from each agent, and updates the environment. It also keeps score for each agent, and optionally displays intermediate results. [p 48]" (initialize env) (display-environment env) (dotimes (i (environment-max-steps env)) (incf (environment-step env)) ;; Deliver percept and get action from each agent (for each agent in (environment-agents env) do (setf (agent-percept agent) (get-percept env agent)) (setf (agent-action agent) (funcall (agent-program agent) (agent-percept agent)))) ;; Execute the actions and otherwise update the world (update-fn env) ;; Update the agent scores, then optionally display the current state (for each agent in (environment-agents env) do (setf (agent-score agent) (performance-measure env agent))) (display-environment env) (when (termination? env) (RETURN))) env)

9. Lecture 2-1CS250: Intro to AI/Lisp “Get Your Red-Hot Lists Here!” Conses are pairs of pointers –First pointer is the car –Rest is the cdr Lists are conses in which: –First pointer is the first element –Second pointer is the rest of the list –No intermediate pointers makes last expensive USER(104): (last (list 'a 'b 'c)) (C)

10. Lecture 2-1CS250: Intro to AI/Lisp Box & Pointer Represent a cons graphically (list ‘a (list ‘b ‘c) ‘d)

11. Lecture 2-1CS250: Intro to AI/Lisp Some Things are More Equal than Others Lisp has multiple definitions of equality Decreasing order of strictness –eq, eql, equal

12. Lecture 2-1CS250: Intro to AI/Lisp eq True if its arguments are the same, identical object; otherwise, returns false (eq 'a 'b) => false (eq 'a 'a) => true (eq 3 3) => true OR => false (eq 3 3.0) => false

13. Lecture 2-1CS250: Intro to AI/Lisp eql True of two objects, x and y, in the folowing cases: 1. If x and y are eq. 2. If x and y are both numbers of the same type and the same value. 3. If they are both characters that represent the same character. (eql 'a 'b) => false (eql 'a 'a) => true (eql 3 3) => true (eql 3 3.0) => false (eql 3.0 3.0) => true (eql #c(3 -4) #c(3 -4)) => true (eql #c(3 -4.0) #c(3 -4)) => false

14. Lecture 2-1CS250: Intro to AI/Lisp equal Generally, returns true if two objects print the same > (setf x (cons ‘a nil)) (A) > (eql x x) T > (equal x (cons ‘a nil)) T

15. Lecture 2-1CS250: Intro to AI/Lisp Mapping over lists Need to do something to every element in a list? Try a mapping function: –mapcar for using the car of successive cdr’s –maplist for successive cdr’s themselves

16. Lecture 2-1CS250: Intro to AI/Lisp mapcar in Action USER(115): (mapcar #'list '(a b c) '(1 2 3 4)) USER(116): (mapcar #'list '(a b c) '(1 2)) ((A 1) (B 2) (C 3)) ((A 1) (B 2))

17. Lecture 2-1CS250: Intro to AI/Lisp Creating an N-Queens Problem (defun nqueens-initial-state (n &optional (explicit? nil) (complete? nil)) (let ((s (make-CSP-state :unassigned (mapcar #'(lambda (var) (make-CSP-var :name var :domain (iota n))) (iota n)) :assigned nil :constraint-fn (if explicit? (let ((constraints (nqueens-constraints n))) #'(lambda (var1 val1 var2 val2) (CSP-explicit-check var1 val1 var2 val2 constraints))) #'nqueens-constraint-fn)))) (if complete? (CSP-random-completion s) s)))

18. Lecture 2-1CS250: Intro to AI/Lisp Unassigned Variables (mapcar #'(lambda (var) (make-CSP-var:name var :domain (iota n))) (iota n)) USER(105): (iota 8) (0 1 2 3 4 5 6 7)

19. Lecture 2-1CS250: Intro to AI/Lisp Unassigned Variables II ((0 (0 1 2 3 4 5 6 7) NIL NIL) (1 (0 1 2 3 4 5 6 7) NIL NIL) (2 (0 1 2 3 4 5 6 7) NIL NIL) (3 (0 1 2 3 4 5 6 7) NIL NIL) (4 (0 1 2 3 4 5 6 7) NIL NIL) (5 (0 1 2 3 4 5 6 7) NIL NIL) (6 (0 1 2 3 4 5 6 7) NIL NIL) (7 (0 1 2 3 4 5 6 7) NIL NIL))

20. Lecture 2-1CS250: Intro to AI/Lisp Recursion Again Recursive function = Base case + Recursive step –Base case will be a conditional test, plus a call that returns Example: General-Search (defun general-search-helper (problem nodes queuing-fn) (let ((node (first nodes))) (if (null node) nil :

21. Lecture 2-1CS250: Intro to AI/Lisp Recursive General Search (if (goal-test problem (node-state node)) node (general-search-helper problem (funcall queuing-fn (rest nodes) (expand node problem)) queuing-fn)...) If we’ve got a node, what do we do next? What if it’s not the goal?

22. Lecture 2-1CS250: Intro to AI/Lisp Put it Together (defun general-search-helper (problem nodes queuing-fn) (let ((node (first nodes))) (if (null node) nil (if (goal-test problem (node-state node)) node (general-search-helper problem (funcall queuing-fn (rest nodes) (expand node problem)) queuing-fn)))))

23. Lecture 2-1CS250: Intro to AI/Lisp Getting it Started... (let ((nodes (make-initial-queue problem queuing-fn)) node) (defun make-initial-queue (problem queuing-fn) (let ((q (make-empty-queue))) (funcall queuing-fn q (list (create-start-node problem))) q)) From simple.lisp : General-Search function How does Make-Initial-Queue work?

24. Lecture 2-1CS250: Intro to AI/Lisp Top-level Function (defun general-search-recursive (problem queueing-fn) "Recursive version of general search" (general-search-helper problem (list (create-start-node problem)) queueing-fn))

25. Lecture 2-1CS250: Intro to AI/Lisp BFS with a List (defun breadth-first-search (problem) (general-search-recursive problem #'append)) What’s the rule for node exploration in BFS? How are new nodes added?

26. Lecture 2-1CS250: Intro to AI/Lisp Sets Sets let you treat lists as sets –Membership –Union, intersection –Set difference

27. Lecture 2-1CS250: Intro to AI/Lisp Sequences Sequences include more than just lists –Ordered series –Lists and vectors Many functions operate on sequences, not just lists: –length, sort, subseq, reverse, every, some, elt

28. Lecture 2-1CS250: Intro to AI/Lisp Structures Create records in Lisp Define structures with the defstruct macro: (defstruct point x y)

29. Lecture 2-1CS250: Intro to AI/Lisp “Big Sale on Constructors & Accessors!” Creating a structure creates: –Constructor ( make-point ) Arguments are passed by keyword –Copy constructor ( copy-point ) –Slot accessor functions ( point-x, point-y ) –Type predicate ( point-p ) New structures are new types

30. Lecture 2-1CS250: Intro to AI/Lisp Default Values for Structure Fields Add a default value (defstruct midterm (difficulty (progn (format t “How hard was it?”) (read))) (max-grade 54) (num-completed nil))

31. Lecture 2-1CS250: Intro to AI/Lisp Customize Automatic Functions (defstruct (point (:conc-name p) (:print-function print-point)) (x 0) (y 0)) (defun print-point (p stream depth) (format stream “# ” (px p) (py p)))