CSE240 (online) Lecture 13

Introduction to Programming Languages
Programming with LISP (Control Structures and Data Structures)
(201805)

Transcript

1. CSE240 – Introduction to Programming Languages (online) Lecture 13: Programming with LISP| Control Structures, Function-Making, and Data Structures Javier Gonzalez-Sanchez javiergs@asu.edu javiergs.engineering.asu.edu Office Hours: By appointment
2. Javier Gonzalez-Sanchez | CSE 240 (online) | Fall 2017 | 2 Control Structures • There are some evaluable lists which are not functions. • These lists are known as macros or special forms. • The control structure if is a special form.
3. Javier Gonzalez-Sanchez | CSE 240 (online) | Fall 2017 | 3 Control Structures • (if (<= 3 2) (* 3 9) (+ 4 2 3)) ; if (3<=2) {return 3*9;} else {return 4+2+3;} 9 • (if (> 2 3) 9) ; if (2>3) {return 9;} else {return nil} NIL • (if (= 2 2) (if (> 3 2) 4 6) 9) 4 • (+ 4 (if (= 2 2) (* 9 2) 7) ) 22
4. Javier Gonzalez-Sanchez | CSE 240 (online) | Fall 2017 | 4 Control Structures • if only allows one test-expression, one then-expression, and one optional-else-expression. • To do more things in the then-expression we need to make a block. Blocks are made with the special form progn, which takes the form: (progn expr1 expr2 expr3 ...) • (if (> 3 2) (progn (print "hello") (print "yo") (print "whassup?") (+ 2 2)) (+ 1 2 3)) "hello" "yo" "whatsup?" 4
5. Javier Gonzalez-Sanchez | CSE 240 (online) | Fall 2017 | 5 Loop (dotimes) dotimes is an iterator with this format (dotimes (var high-val optional-return-val) expr1 expr2 …) • (dotimes (x 4) (print "hello")) "hello" "hello" "hello" "hello" NIL • (setf bag 2) 2 • (dotimes (x 3) (setf bag (* bag bag))) NIL • (print bag) 256
6. Javier Gonzalez-Sanchez | CSE 240 (online) | Fall 2017 | 6 Global Variables • Variables are set with the macro setf. • (setf x (* 3 2)) 6 • x 6 • (setf y (+ x 3)) 9
7. Javier Gonzalez-Sanchez | CSE 240 (online) | Fall 2017 | 7 Local Variables • let declares local variables with each declaration. Then it evaluates the expressions in order (as a block). • let returns the value of the last expression. • (setf x 4) (let ((x 3)) ; x declared local (print x) (setf x 9) ; change the value of x (print x) (+ x x) ;this is the returned value ) 3 9 18 • x ;outside the let, we're back to global again 4
8. Javier Gonzalez-Sanchez | CSE 240 (online) | Fall 2017 | 8 Nested Variable Scope • (let ((x 3) (y (+ 4 9))) (* x y)) 39 • (let ((x 3)) (print x) (let (x) (print x) (let ((x "hello")) (print x)) (print x)) (print x) (print ”end")) 3 NIL "hello" NIL 3 "end" "end"
9. Javier Gonzalez-Sanchez | CSE 240 (online) | Fall 2017 | 9 Function Making • functions are created by calling a function-making macro. This macro is called defun. • the function returns the value of the last expression. (defun function-name-symbol (param1 param2 param3 ...) expr1 expr2 expr3 ... )
10. Javier Gonzalez-Sanchez | CSE 240 (online) | Fall 2017 | 10 Function Making • (defun do-hello-world ( ) "Hello, World!") DO-HELLO-WORLD • (do-hello-world) "Hello, World!" • (defun add-four (x) (+ x 4)) ADD-FOUR • (add-four 7) 11 • (defun hypotenuse (length width) (sqrt (+ (* length length)(* width width)))) HYPOTENUSE • (hypotenuse 7 9) 11.4017
11. Javier Gonzalez-Sanchez | CSE 240 (online) | Fall 2017 | 11 Function Making • (defun first-n-chars (string n reverse-iT) (if reverse-iT (subseq (reverse string) 0 n) (subseq string 0 n))) FIRST-N-CHARS • (first-n-chars "hello world" 5 nil) "hello" • (first-n-chars "hello world" 5 t) "dlrow" • (first-n-chars "hello world" 5 2013) "dlrow"
12. Javier Gonzalez-Sanchez | CSE 240 (online) | Fall 2017 | 12 Data Structures The only data structure is List • (quote (hello world 1 2 3)) (HELLO WORLD 1 2 3) • '(hello world 1 2 3) (HELLO WORLD 1 2 3) • (quote (what is (going on) here?)) (WHAT IS (GOING ON) HERE?) • (quote my-symbol) MY-SYMBOL • (quote (+ 4 (* 3 2 9))) (+ 4 (* 3 2 9))
13. Javier Gonzalez-Sanchez | CSE 240 (online) | Fall 2017 | 13 Data Structures • first returns the first item in a list. The old name of first is car (content of the address). • rest returns a list consisting of everything but the first item. It does not damage the original list. The old name of rest is cdr (content of the decrement register). • append hooks multiple lists together. • cons takes an item and a list, and returns a new list consisting of the old list with the item tacked on the front.
14. Javier Gonzalez-Sanchez | CSE 240 (online) | Fall 2017 | 14 Data Structures • ( setf myList '( (A B) C (D) ) ) ((A B) C (D)) • (car (car myList) ) ;( first ( first ) ) A • (cdr( car myList)) ;( last ( first ) ) (B) • (car (cdr myList)) ;( first ( last ) ) C
15. Javier Gonzalez-Sanchez | CSE 240 (online) | Fall 2017 | 15 Data Structures • ( setf myList2 '(A (B () (C () () )) (D (E () () ) () ) ) ) (A (B NIL (C NIL NIL)) (D (E NIL NIL) NIL)) • (car (car myList2)) ;( first ( first (L)) Error: Cannot take CAR of A. • (cdr( car myList2)) ;( last ( first (L)) Error: Cannot take CDR of A. • (car (cdr myList2)) ;( first ( last (L)) (B NIL (C NIL NIL))
16. Javier Gonzalez-Sanchez | CSE 240 (online) | Fall 2017 | 16 Loop (dolist) • (dolist (x '(a b c d e)) (print x)) A B C D E NIL dolist is an iterator with this format (dolist (var list-to-iterate-over optional-return-val) expr1 expr2 …)
17. Javier Gonzalez-Sanchez | CSE 240 (online) | Fall 2017 | 17 Loop (dolist) • (defun my-reverse (list) (let (new-list) ; empty list (dolist (x list) (setf new-list (cons x new-list)) ) new-list) ) MY-REVERSE • (my-reverse '(a b c d e f g)) (G F E D C B A)
18. CSE240 – Introduction to Programming Languages (online) Javier Gonzalez-Sanchez javiergs@asu.edu Fall 2017 Disclaimer. These slides can only be used as study material for the class CSE240 at ASU. They cannot be distributed or used for another purpose.