1. Lisp Recitation (cse471/598 Fall 2007 ) Aravind Kalavagattu

2. Outline: Setting up the environment  LISP-in-a-box LISP  Datatypes  Expressions  Functions  Conditionals  Looping  Others CSE 471.. LISP

3. Functional Programming Function is the basic element. Both data and function are treat as object. The parameter could be a function. Basic rule: the parameters of a function should not be changed. (But there are some exceptions like sort, incf, decf)

4. An example LISP program! LISP in a box! (defun helloworld() (format t “hello world”))

5. Expression Evaluation You type an expression, the interpreter responds by displaying the results of the evaluation of that expression. Ex. >486 The interpreter will respond 486 Prefix Notation The leftmost element in the list is the operator and the other elements are operands. >(+ 137 349) 486 Compound expressions are formed by combining other expressions. >(/ (- 7 1) (- 4 2)) 3 ** The way we call functions also is a ‘ Prefix notation ’ with function name followed by the arguments.

6. Data Atoms  Numbers >1 >334  Symbols a Horse Variables, Arrays, Vectors, Structures  (make-array ‘(2 3)) (aref )  (defstruct employee age first-name last-name sex children) EMPLOYEE Lists  (1 2 3)  (7 a horse) QUOTE operator  Takes a single argument, and returns it verbatim > (quote (+ 3 5)) (+ 3 5)

7. Data Structure - Lists Using Quote:- ‘(1 2 3) also (quote ( 1 2 3)) (1 2 3) Using CAR:- (CAR ‘( 1 2 3 4)) 1 Using CDR:- (CDR ‘( 1 2 3)) ( 2 3) - cadr, cadddr, nthcdr !

8. Using ‘ list ’ : (list 'a '(a s d f))  List takes all its arguments and makes a list with them as elements Using Cons :- (cons 0 ‘ (1 2 3)) adds the element 0 to the head of the list (1 2 3) (0 1 2 3) Using Append : – (append ‘ (1 2) ‘ (3 4 5)) Creates a new list out of existing lists (1 2 3 4 5) List can also be interpreted as sets, hashtables, trees, sequences, stacks, association-lists.

9. Variables Assignment  (setf x (list ‘a ‘b ‘c)) (A B C)  (setf (car x) ‘n) N  (setf a 1 b 2 c 3) { a=1; b=2; c=3}

10. Variables Local:  (let ( ( ) ( ) … ( ) ) ( ) ) Example: (let ((a 1) (b 3)) (+ 33 a b)) >> 37 Global:  (defparameter *pi* 3.14)  (defconstant +limit+ 100)

11. Function (defun ( ) ) Example:  (defun square (x) (* x x))  SQUARE > (square 2)  4  > (square 1.4142158)  2.0000063289696399  Symbolp, listp  Truth and False values  (null nil)  true

12. Conditionals Comparisons: >=, <=, eql, eq If (if ) Ex: (defun absdiff (x y) (if (> x y) (- x y) (- y x) )) Cond (like “switch” in C/C++) (cond (A B) (C D) (t E)) (t E)  is the ‘default’ equivalent Example: (defun absdiff (x y) (cond ((> x y) (- x y)) (t (- y x)))) ** Others: when, until, always

13. Looping (dolist ( ) ) (dotimes ( ) ) Examples:  (defun num-sublists-i (lis) (let ((result 0)) (dolist (next lis result) (if (listp next) (setf result (1+ result))))))  (defun power-i (x y) (let ((result 1)) (dotimes (count y result) (setf result (* x result)))))

14. RECURSION Compute factorial: (defun factorial (n) (if (= n 0) 1 (* n ( factorial (- n 1) ) ) ) )

15. Input and Output > (progn (format t “Please enter your name: ”) (read-line)) > (prin1 “hello”) Note: There are many variants.

16. (defun f-to-c (ftemp) (let ((ctemp (* (- ftemp 32) 5/9))) (format t "~%~s degrees Fahrenheit is ~%~s degrees Celsius~%" ftemp ;; first ~s (float ctemp)) ;; second ~s ctemp)) ;; return ratio value - ;; Commenting

17. Other Imp. LISP stuff Mapcar  The MAPCAR form is an "iterator" that applies a function repeatedly, to each element of a list and returns a list of the results. For example: > (MAPCAR 'ATOM '(DOG (CAT HORSE) FISH)) (T NIL T) Apply  Apply takes its first argument and applies it as a function to the list of items making up the last. For example: >(apply '* '(1 2 3 4)) 24 Lambda  You can think of a lambda expression as an anonymous function. > (setf product '(lambda (x y) (* x y))) (LAMBDA (X Y) (* X Y)) > product (LAMBDA (X Y) (* X Y)) > (apply product '(3 4)) 12

18. Loading a lisp file into lisp-in-a-box (windows) ( load “ ”)  The filename is the path with “\” escaped  Example: (load "C:\\Documents and Settings\\Aravind\\Desktop\\code.lisp")

19. Suggested programming style Write short functions, where each function provides a single, well-defined operation Use proper indentation Program idea with recursion Top-down approach with abstraction

20. Useful commands for lisp-in-a-box / emacs Ctrl-c Ctrl-d; Ask for the description Alt-p; Run through the history Ctrl-c Ctrl-q; complete all the parenthesis Ctrl-c Ctrl-z; Return to the interpreter Ctrl-c Ctrl-c; Compile a function Ctrl-c Ctrl-k; Compile and load a file Other basic commands for emacs

21. How to deal with problems TA  We can discuss one-on-one during my office hours! Where you can ask: 1. Newsgroup: comp.lang.lisp 2. Search Google. 3. Check the documentation of specified functions. 4. Discuss with each other

22. CSE 471.. What kind of projects (LISP)?  Partial code is given many times  Understand its working and extend for tasks in the project Project 0?  Finish a good full tutorial on LISP and start the project LISP Primer Common Lisp tutorials  Use LISP references whenever needed

23. “ Lisp is a language for smart people. ” Have Fun with Lisp Questions?