CSE240 Lecture 21

Transcript

1. jgs CSE 240 Introduction to Programming Languages Lecture 21: Lists

   in LISP Javier Gonzalez-Sanchez javiergs@asu.edu PERALTA 230U Office Hours: By appointment

2. Javier Gonzalez-Sanchez | CSE240 | Spring 2020 | 2 jgs

   Announcement § Homework 04 and Quiz 03 are due Today

3. jgs Previously Atomic Expressions

4. Javier Gonzalez-Sanchez | CSE240 | Spring 2020 | 4 jgs

   Atomic Expressions § -3 § 2.43 § 123342303923412323411323234012923492341231230234923410239234412 § #C(3.2 2) ; the complex number 3.2 + 2i § 2/3 ; the fraction 2/3. It is NOT divide 2 by 3 § -3.2e25 ; the number -3.2 x 10^25 § #\g ; characters starts with #\ § #\{ § #\\ ; the character '\' § #\tab
 § #\newline § 
#\space
 § #\backspace
 § #\escape

5. Javier Gonzalez-Sanchez | CSE240 | Spring 2020 | 5 jgs

   Atomic Expressions § "Hello, World!" § "It's a glorious day." § "He said \"No Way!\" and then he left." § "I think I need a backslash here: \\ Ah, that was better." § t ; true § nil ; false

6. jgs Lists

7. Javier Gonzalez-Sanchez | CSE240 | Spring 2020 | 7 jgs

   Everything is a List § (+ 27/32 32/57) 2563/1824 § (* 2.342 3.2e4) 74944.0 § (* 2.342 9.212 -9.23 3/4) ; You can mix number types -149.34949 § (/ 3 5) ; The return type stays as general as possible 3/5 § (/ 3.0 5) ;Here LISP had no choice: convert to a float 0.6 § (1+ 3) 4

8. Javier Gonzalez-Sanchez | CSE240 | Spring 2020 | 8 jgs

   Everything is a List § (string-upcase "How about that!") "HOW ABOUT THAT!" § (reverse "Four score and seven years ago") "oga sraey neves dna erocs ruoF" § (length "Four score and seven years ago") 30 § (sqrt 2) 1.4142135 § (sqrt -1.0) #C(0 1.0) § (SqRt -1.0) ;LISP symbols are case-insensitive #C(0 1.0)

9. Javier Gonzalez-Sanchez | CSE240 | Spring 2020 | 9 jgs

   Function Arguments § Some functions have NOT a fixed number of arguments: (+ 100 231 201 921 221 231 -23 12 -34 134) § Some functions have a fixed number of arguments and optional arguments: (subseq "Four score and seven years ago" 9) "e and seven years ago” (subseq "Four score and seven years ago" 9 23) "e and seven ye"

10. Javier Gonzalez-Sanchez | CSE240 | Spring 2020 | 10 jgs

    Predicates (boolean functions) § LISP has a special name for functions which return "true" (usually t) or "false" (nil). These functions are called predicates. • (= 4 3) ; is 4 == 3 ? NIL • (< 3 9) ; is 3 < 9 ? T • (numberp "hello") ; is "foo" a number? NIL • (oddp 9) ; is 9 an odd number? T

11. Javier Gonzalez-Sanchez | CSE240 | Spring 2020 | 11 jgs

    Errors § Errors stop the program execution • (/ 1 0) *** - division by zero • (blah-blah-blah 1 0 "foo") *** - EVAL: the function BLAH-BLAH-BLAH is undefined

12. Javier Gonzalez-Sanchez | CSE240 | Spring 2020 | 12 jgs

    Recursion § When a list contains another list among its expressions, the evaluation procedure is recursive. • (+ 33 (* 2.3 4) 9) 51.2 • (+ (length "Hello World") 44) 55 • (* (+ 3 2.3) (/ 3 (- 9 4))) ;in C++: (3+2.3) * (3 / (9-4)) 3.1800003 • (log (log (log 234231232234234123))) 1.3052895 • (+ (* (sin 0.3) (sin 0.3)) ; expressions may use multiple lines (* (cos 0.3) (cos 0.3))) ; sin(0.3)^2 + cos(0.3)^2 1.0000001 ; = 1. Rounding inaccuracy

13. Javier Gonzalez-Sanchez | CSE240 | Spring 2020 | 13 jgs

    Recursion § (and (< 3 (* 2 5)) (not (>= 2 6))) ; (3 < 2 * 5) && !(2 >= 6) T § (print (+ 2 3 4 1)) 10 10 § (+ (* 2 3) (/ 3 2) 9) 33/2

14. jgs CSE 240 Introduction to Programming Languages Javier Gonzalez-Sanchez javiergs@asu.edu

    Spring 2020 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.