Comparative Programming Languages

1. Language Comparison: Scheme, Smalltalk, Python, Ruby, Perl, Prolog, ML, C++/STL, Java Comparative Programming Languages

2. Fundamentals of Functional Programming Languages • The objective of the design of a functional programming language (FPL) is to mimic mathematical functions to the greatest extent possible • The basic process of computation is fundamentally different in a FPL than in an imperative language • In an imperative language, operations are done and the results are stored in variables for later use • Management of variables is a constant concern and source of complexity for imperative programming • In an FPL, variables are not necessary, as is the case in mathematics CS 363 Spring 2005 GMU 2

3. Fundamentals of Functional Programming Languages • In an FPL, the evaluation of a function always produces the same result given the same parameters • This is called referential transparency CS 363 Spring 2005 GMU 3

4. Lisp • Lisp – based on lambda calculus (Church) • Uniform representation of programs and data using single general data structure (list) • Interpreter based (written in Lisp) • Automatic memory management • Evolved over the years • Dialects: COMMON LISP, Scheme CS 363 Spring 2005 GMU 4

5. Smalltalk – Object Orientation • Smalltalk – a dynamically typed object oriented programming and functional language designed at Xerox PARC by Alan Kay, Dan Ingalls, Ted Kaehler, Adele Goldberg, during the 1970s. • Released as Smalltalk-80 • Influenced the development of languages such as Objective-C, Java and Ruby • Everything is an object • Everything is available for modification. If you want to change the IDE, you can do it • Types are dynamic -- you don't have to define types in the code • Garbage collection is built in, invisible to the developer. 5

6. Squeak • Squeak is an open, highly-portable Smalltalk-80 implementation whose virtual machine is written entirely in Smalltalk • The image below was created in Squeak, and illustrates several of Squeak's abilities, including the ability to scale and rotate bitmap images at any colour depth, anti-aliased TrueType fonts and vector graphics 6

7. Ruby • Ruby – combines syntax inspired by Python and Perl with Smalltalk-like object-oriented features • Ruby is an interpreted language. • Created by Yukihiro "Matz" Matsumoto, started working on Ruby in Feb. 1993 and released it to the public in 1995. • Name chosen to reflect the language's Perl heritage. • Designed Ruby to follow the principle of least surprise - the language should be free from traps and inconsistencies of other languages 7

8. Python • Python is an interpreted, interactive programming language created by Guido van Rossum in 1990 • Originally as a scripting language for Amoeba OS capable of making system calls. • Amoeba distributed operating system is a microkernel-based research operating system written by Andrew S. Tanenbaum at Vrije Universiteit • The aim of the project was to build a timesharing system that appeared to the user as a single machine even though it was running on multiple machines. 8

9. Python • Python • Often compared to Tcl, Perl, Scheme, Java, and Ruby • Developed as an open source project, managed by the non-profit Python Software Foundation. • Python is a multi-paradigm language, like Perl, Oz or C++ and unlike Smalltalk or Haskell • Rather than forcing coders to adopt one particular style of coding, it permits several • Object orientation, structured programming, functional programming are all supported • Python is dynamically type-checked and uses garbage collection for memory management • origin of the name - after the television series Monty Python's Flying Circus 9

10. Python • Python (from wikipedia) • Many similarities to Perl • However, Python's designers reject Perl's exuberant syntax in favor of a more spare, less cluttered one • As with Perl, Python's developers expressly promote a particular "culture" or ideology (http://python.org/dev/culture.html) based on what they want the language to be, favoring language forms they see as "beautiful", "explicit" and "simple". • Although Python is sometimes classified as a "scripting language", it has been used to develop many large software projects such as the Zope application server 10

11. Scheme (dr scheme, guile) (define (gcd u v) (if ( = v 0) u (gcd v (remainder u v)) ) ) (define (reverse l) (if (null? l) l (append (reverse (cdr l))(list (car l))) ) ) CS 363 Spring 2005 GMU 11

12. Scheme (dr scheme, guile) Using guile (gnu scheme): (load "slides.scm") (gcd 56 108) --> 4 (reverse '(2 3 556)) --> (556 3 2) CS 363 Spring 2005 GMU 12

13. Common Lisp (clisp) (defun mygcd (u v) (if (= v 0) u (mygcd v (rem u v)) ) ) (defun myreverse (l) (if (null l) l (append (myreverse (cdr l))(list (car l))) ) ) ;; (load "slides.lsp"), (mygcd 56 108) --> 4 ;; (myreverse '(2 3 556)) --> (556 3 2) 13

14. Smalltalk (Squeak - inisqueak) myGcd: numTwo " 112 myGcd: 224 --> 112” (numTwo = 0) ifTrue: [^self]. ^numTwo myGcd: self \\ numTwo. myReverse "#(1 2 3 43 a b) myReverse -> ($b $a 43 3 2 1 )" (self size = 0) ifTrue: [^self]. ^self allButFirst myReverse, self first asOrderedCollection. 14

15. Gnu-Smalltalk – gst !SequenceableCollection methodsFor: 'algorithms'! "Or use Array, but that limits your objects." myCount " #(1 2 3 $a $b $c myCount! --> 6 In gst: Filestream inFile: count.st " (self size = 0) ifTrue: [^0]. ^(1 + (self copyFrom: 2) myCount). ! 15

16. Gnu-Smalltalk – gst (cont.) myReverse "#(1 2 3 43 a b) myReverse -> • ($b $a 43 3 2 1 )" | temp | (self size = 0) ifTrue: [^self]. temp := OrderedCollection new: 1. temp add: self first. ^(self copyFrom: 2) myReverse, temp. !! 16

17. Gnu-Smalltalk – gst (cont.) !Number methodsFor: 'algorithms'! myGcd: numTwo "120 myGcd: 200! --> 40" (numTwo = 0) ifTrue: [^self]. ^numTwo myGcd: self \\ numTwo. !! 17

18. Ruby (ruby) def myGcd(numOne, numTwo) if numTwo == 0 return numOne end return myGcd(numTwo, numOne % numTwo) end def myReverse(list) if list.length == 1 return list end return myReverse(list[1..list.length-1]).concat([list[0]]) end 18

19. Ruby - “Class version”count.rb class Integer def myGcd(numTwo) if numTwo == 0 return self else return numTwo.myGcd(self % numTwo) end end end - load “file.rb” into the Ruby interpreter (eval.rb) - 120.myGcd(500) --> 20 19

20. Ruby - “Class version” class Integer def greet print "Hello world\n" end def plus(numTwo) return self + numTwo end def times(numTwo) return self * numTwo end end - load “file.rb” into the Ruby interpreter (eval.rb) - 120.greet --> “Hello..”, 3.plus(4).times(5) -> 35 20

21. Ruby (non-class vers.) def myCount (mylist) if mylist.length == 0 return 0 else return 1 + myCount(mylist[1..mylist.length-1]) end end print "Length of [1,2,3,4,5,6]= ", myCount([1,2,3,4,5,6]), "\n" To run: ruby count.rb 21

22. Ruby (class vers.) class Array def myCount if self.length == 0 return 0 else return 1 + self[1..self.length].myCount end end end This version is “object oriented”... [3,4,5,6,7,78].myCount --> 6 22

23. Python (python) def myGcd(numOne, numTwo): if(numTwo == 0): return numOne return myGcd(numTwo, numOne % numTwo) def myReverse(mylist): if len(mylist) == 1: return mylist return myReverse(mylist[1:len(mylist)]) + myReverse([mylist[0]]) 23

24. Python (python) def myCount (mylist): if len(mylist) == 0: return 0 else: return 1 + myCount(mylist[1:len(mylist)]) print "Length of [1,2,3,4,5,6]= ", myCount([1,2,3,4,5,6]) To run: python count.py 24

25. Perl sub gcd { if ($_[1] == 0) { return $_[0]; } else { return gcd($_[1], $_[0] % $_[1]); } } sub count { my @ls; @ls = @_; if (scalar(@ls) == 1) { 1; } else { count(@ls[1..$#ls]) + 1; } } 25

26. Perl sub myReverse { my @templis; if (scalar(@_) == 0) { return (); } else { @templis = myReverse(@_[1..$#_]); push(@templis, $_[0]); return @templis; } } 26

27. Prolog gcd(Num1, 0, Num1). gcd(Num1, Num2, GCD) :- Rem is Num1 mod Num2, gcd(Num2, Rem, GCD). count([],Total , Total). count([_|Rest], Counter, TotalCount) :- NewCount is Counter + 1, count(Rest, NewCount,TotalCount). /* consult('gcd.pl'). gcd(28, 100, X). count([3,4,5,6,7],0, X). */ 27

28. Prolog append([],List, List). append([First|Rest], List2, [First|List3]) :- append(Rest, List2, List3). myreverse([],[]). myreverse([First|[]],[First]). myreverse([First|Rest], NewList) :- myreverse(Rest, ReversedList), append(ReversedList,[First], NewList). /* ?- consult('reverse.pl'). ?- myreverse([11,23, 0,42,18,90, 1],X). X = [1, 90, 18, 42, 0, 23, 11] */ 28

29. ML (sml) fun gcd(num1, 0) = num1 | gcd(num1,num2) = gcd(num2, num1 mod num2); fun count([]) = 0 | count(first::rest) = 1 + count(rest); (* - use "gcdcount.sml"; - gcd(28, 124); val it = 4 : int - count([45,2,7,8,1,23,18]); val it = 7 : int *) 29

30. ML (sml) fun reverse(L) = if L = nil then nil else reverse(tl(L)) @ [hd(L)]; fun reverse2([]) = [] | reverse2(first::rest) = reverse2(rest) @ [first] (* [] can be used for nil - use "reverse.sml"; - reverse2([1,2,3,4]); val it = [4,3,2,1] : int list -val x = [[1,2],[3,4]] : int list list - reverse(x); - val it = [[3,4],[1,2]] : int list list *) 30

31. C++ int gcd(int num1, int num2) { if (num2 == 0) return num1; else return gcd(num2, num1 % num2); } 31

32. C++ (STL) int count(list<int> lis) { if (lis.size() == 0) return 0; else { lis.pop_front(); return 1 + count(lis); } } 32

33. C++ (STL) list<int> reverse(list<int> lis) { if (lis.size() == 0) return lis; else { int first = *lis.begin(); lis.pop_front(); list<int> reversed; reversed = reverse(lis); reversed.push_back(first); return reversed; } } 33

34. Java int gcd(int num1, int num2) { if (num2 == 0) return num1; else return gcd(num2,num1 % num2); } 34

35. Java int count(List lis) { if (lis.isEmpty()) // or lis.size() == 0 return 0; else return 1 + count(lis.subList(1, lis.size())); } 35

36. Java List reverse(List lis) { if (lis.isEmpty()) return lis; else { Integer first = (Integer)lis.get(0); List temp = reverse(lis.subList(1,lis.size())); temp.add(temp.size(), first); return temp; } } 36

37. Squeak Browser Window – Lists classes and methods in classes

38. Squeak Workspace WindowTo “run” each line, middle-button click, choose “do it” or “print it”

39. Squeak Transcript WindowTo “run” each line, middle-button click, choose “do it” or “print it”

40. Gnu Smalltalk Browser Window

41. Worksheet window Transcript window To “run” a line, right click and choose “do it” and/or “print it” Gnu Smalltalk, X11Worksheet and Transcript

42. Note the use of “!” at the end of each line. Also, printNl is specific to gst. Gnu Smalltalk - gst

43. Ruby – example run, see count.rb

44. Ruby – example run from eval.rb

45. Python – example run, see count.rb