CSE240 Lecture 20

Introduction to Programming Languages
Programming with LISP
(202111)

Transcript

1. jgs
   CSE 240
   Introduction to Programming Languages
   Lecture 20: Programming with LISP
   Dr. Javier Gonzalez-Sanchez
   javiergs@asu.edu
   javiergs.engineering.asu.edu | javiergs.com
   PERALTA 230U
   Office Hours: By appointment
   

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2. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 2
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   Functional Paradigm
   

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3. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 3
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   Semantic
   Functional Paradigm
   Key idea:
   Focus on higher level of abstraction
   (free from programming details)
   Features:
   Simpler semantic: no data types, and
   a simpler syntax
   

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4. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 4
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   Syntax
   § Uniform representation of instructions and data using a single general
   format– a list.
   (functionId param1 param2 param3 ...)
   • (+ 3 2 7 9) ; add 3+2+7+9 and return the result
   21
   • (* 4 2.3) ; multiply 4 by 2.3 and return the result
   9.2
   • (subseq "Hello, World" 2 9)
   "llo, Wo"
   

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5. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 5
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   Functional Programming
   § Language: we will use LISP (LISt Processing).
   § It uses an interpreter.
   § Automatic management of memory.
   

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6. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 6
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   You need an Interpreter
   § LispWork Personal Edition –
   http://www.lispworks.com/downloads/index.html
   § Compile Lisp Online –
   http://rextester.com/l/common_lisp_online_compiler
   § Steel Bank Common Lisp –
   http://www.sbcl.org/platform-table.html
   

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7. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 7
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   Functional Programming
   § A program is a set of lists and they are enclosed with parenthesis.
   § We use lists to represent functions; in a function the first element of the list is the id
   of the function and the rest are parameter(s)
   § Whitespace separate function id and parameters
   § Examples:
   ( print "Hello World" )
   ( + 2 2 )
   ( sqrt 2 )
   

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8. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 8
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   Important Notice !
   

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9. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 9
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   Everything is a List
   § A function ID (symbol) is a series of characters other than whitespace, parentheses
   ( ), pound ( # ), quote ( ' ), double-quote ( " ), period ( . ), or back quote ( ` ).
   § A function ID (symbol) may not take the form of numbers.
   § It's very common for symbols to have hyphens ( - ) or asterisks ( * ) in them.
   § There are NOT operators! only functions
   § Symbols (function ID) are case-INSENSITIVE.
   

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10. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 10
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    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
    

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11. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 11
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    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
    

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12. jgs
    Lists
    

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13. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 13
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    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
    

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14. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 14
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    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)
    

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15. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 15
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    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"
    

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16. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 16
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    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
    

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17. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 17
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    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
    

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18. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 18
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    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
    

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19. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 19
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    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
    

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20. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 20
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    Questions
    

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21. jgs
    CSE 240 Introduction to Programming Languages
    Javier Gonzalez-Sanchez, Ph.D.
    javiergs@asu.edu
    Fall 2021
    Copyright. These slides can only be used as study material for the class CSE240 at Arizona State University.
    They cannot be distributed or used for another purpose.
    

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