Comparative Programming Languages

Language Comparison: Scheme, Smalltalk, Python, Ruby, Perl, Prolog, ML, C++/STL, Java

CS 363 Spring 2005 GMU 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 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 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

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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.

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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

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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

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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.

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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

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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

CS 363 Spring 2005 GMU 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 12

Scheme (dr scheme, guile)Using guile (gnu scheme):

(load "slides.scm")(gcd 56 108) --> 4(reverse '(2 3 556)) --> (556 3 2)

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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)

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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.

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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).

!

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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.!!

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Gnu-Smalltalk – gst (cont.)

!Number methodsFor: 'algorithms'!

myGcd: numTwo "120 myGcd: 200! --> 40"

(numTwo = 0) ifTrue: [^self]. ^numTwo myGcd: self \\ numTwo.!!

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Ruby (ruby)def myGcd(numOne, numTwo)

if numTwo == 0return numOne

endreturn myGcd(numTwo, numOne % numTwo)

end

def myReverse(list)if list.length == 1

return listendreturn myReverse(list[1..list.length-1]).concat([list[0]])

end

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Ruby - “Class version”count.rb

class Integerdef myGcd(numTwo)

if numTwo == 0return self

else return numTwo.myGcd(self % numTwo)

endend

end

- load “file.rb” into the Ruby interpreter (eval.rb)

- 120.myGcd(500) --> 20

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Ruby - “Class version”class Integer

def greetprint "Hello world\n"

enddef plus(numTwo)

return self + numTwoenddef times(numTwo)

return self * numTwoend

end- load “file.rb” into the Ruby interpreter

(eval.rb)- 120.greet --> “Hello..”, 3.plus(4).times(5) -> 35

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Ruby (non-class vers.)def myCount (mylist)

if mylist.length == 0return 0

else return 1 + myCount(mylist[1..mylist.length-1])

endend

print "Length of [1,2,3,4,5,6]= ", myCount([1,2,3,4,5,6]), "\n"

To run: ruby count.rb

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Ruby (class vers.)class Array

def myCountif self.length == 0

return 0else

return 1 + self[1..self.length].myCountend

endend

This version is “object oriented”...

[3,4,5,6,7,78].myCount --> 6

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Python (python)def myGcd(numOne, numTwo):

if(numTwo == 0):return numOne

return myGcd(numTwo, numOne % numTwo)

def myReverse(mylist):if len(mylist) == 1:

return mylistreturn myReverse(mylist[1:len(mylist)]) + myReverse([mylist[0]])

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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

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Perlsub 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;}

}

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Perlsub myReverse {

my @templis;if (scalar(@_) == 0) {

return ();} else {

@templis = myReverse(@_[1..$#_]);push(@templis, $_[0]);return @templis;

}}

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Prologgcd(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).*/

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Prologappend([],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] */

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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*)

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ML (sml)fun reverse(L) =

if L = nil then nilelse 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 *)

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C++

int gcd(int num1, int num2) {if (num2 == 0)

return num1;else

return gcd(num2, num1 % num2);}

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C++ (STL)

int count(list<int> lis) {if (lis.size() == 0)

return 0;else {

lis.pop_front();return 1 + count(lis);

}}

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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;

}}

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Javaint gcd(int num1, int num2) {

if (num2 == 0) return num1;

else return gcd(num2,num1 % num2);

}

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Javaint count(List lis) {

if (lis.isEmpty()) // or lis.size() == 0

return 0;else

return 1 + count(lis.subList(1, lis.size()));

}

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JavaList 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;

}}

Squeak Browser Window – Lists classes and methods in classes

Squeak Workspace WindowTo “run” each line, middle-button click, choose

“do it” or “print it”

Squeak Transcript WindowTo “run” each line, middle-button click, choose

“do it” or “print it”

Gnu Smalltalk Browser Window

Gnu Smalltalk, X11Worksheet and Transcript

Worksheet window Transcript windowTo “run” a line, right click and choose “do it” and/or “print it”

Gnu Smalltalk - gst

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

Ruby – example run, see count.rb

Ruby – example run from eval.rb

Python – example run, see count.rb