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

2. Projects What’s expected Project ideas Lecture 2-1
CS250: Intro to AI/Lisp

3. “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)
Lecture 2-1
CS250: Intro to AI/Lisp

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

5. 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
Lecture 2-1
CS250: Intro to AI/Lisp

6. More on eq Crazy things can happen Question from last time:
Implementations can “collapse” constants
(eq “Foo” “Foo”) could be TRUE or FALSE
If interpreted, it’s always FALSE
Question from last time:
(eq ‘(a .b) ‘(a . b)) could be TRUE or FALSE
(eq (cons ‘a ‘b) (cons ‘a ‘b)) is FALSE
Lecture 2-1
CS250: Intro to AI/Lisp

7. 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 ) => true
(eql #c(3 -4) #c(3 -4)) => true
(eql #c(3 -4.0) #c(3 -4)) => false
Lecture 2-1
CS250: Intro to AI/Lisp

8. eq vs. eql eql tells whether two objects are conceptually the same
eq tells whether two objects are implementationally the same
Lecture 2-1
CS250: Intro to AI/Lisp

9. = Numeric comparisons USER(3): (= 3 3 3 3) T USER(4): (= 3 3.0 3 3 3)
NIL
Lecture 2-1
CS250: Intro to AI/Lisp

10. Sequences Sequences are ordered “sets” Many useful functions:
Lists + vectors
Many useful functions:
elt reverse map remove
length nreverse some delete
...
Lecture 2-1
CS250: Intro to AI/Lisp

11. Association lists Easy lookup tables Try this
(setf nickname '(("Red Sox" . "Losers")
("Mets" . "Wannabes")
("Yankees" . "World champions")))
What is returned by:
(assoc “Red Sox” nickname)
Lecture 2-1
CS250: Intro to AI/Lisp

12. Keyword args Keywords enable flexibility in arguments
Playing with args:
&rest
&optional
&key
Lecture 2-1
CS250: Intro to AI/Lisp

13. The rest of the story How does #’+ work?
How to handle an unknown number:
Use a list
Use rest
Testing for nil
(defun any-nil-p (&rest all-values)
(notevery
#'null
(mapcar #'null all-values)))
Lecture 2-1
CS250: Intro to AI/Lisp

14. Optional parameters Add an optional parameter with a default value
((lambda (a &optional (b 2))
(+ a (* b 3)))
4 5)
((lambda (a &optional (b 2))
(+ a (* b 3))) 4)
Lecture 2-1
CS250: Intro to AI/Lisp