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Intelligent Agents

Intelligent Agents. Lecture 3-2 October 14 th , 1999 CS250. Projects. What’s expected Project ideas. “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

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Intelligent Agents

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

  2. Projects • What’s expected • Project ideas 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) CS250: Intro to AI/Lisp

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

  6. More on eq • Crazy things can happen • 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 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 3.0 3.0) => true (eql #c(3 -4) #c(3 -4)) => true (eql #c(3 -4.0) #c(3 -4)) => false 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 CS250: Intro to AI/Lisp

  9. = • Numeric comparisons USER(3): (= 3 3 3 3) T USER(4): (= 3 3.0 3 3 3) T USER(5): (= 2 3.0 3 3 3) NIL CS250: Intro to AI/Lisp

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

  12. Keyword args • Keywords enable flexibility in arguments • Playing with args: • &rest • &optional • &key 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))) 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) CS250: Intro to AI/Lisp

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