Einführung in die Informatik 2. Programming Languages, Paradigms and Technology Institut für Informatik und angewandte Mathematik

Einführung in die Informatik

2. Programming Languages, Paradigms and Technology

Institut für Informatik und angewandte Mathematik

© Oscar Nierstrasz 2

Roadmap

> What is a programming language?> Programming = modeling> Evolution> Trends and Challenges

Programming Languages, Paradigms and Technology

© Oscar Nierstrasz


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Übersicht

Informatik

Theorie(Automaten und formale Sprachen, Berechenbarkeit, Komplexität, Logik, Algorithmen)

Praxis(Programmiersprachen, Betriebssysteme, Netzwerke &Verteilte Systeme, Software Engineering, Datenbanken, Rechnerarchitektur)

Schnittstellen zur Aussenwelt(Mensch-Maschine Schnittstelle, Computer-vision, Computergrafik, Sensornetze, Künstliche Intelligenz, Computerlinguistik)

Wirtschaftsinformatik

Anwendungs-software

Wissenschaftliche Anwendungen(Modellierung und Simulation, Biologie, Physik, Chemie, Sozialwissenschaften, etc.)

Informatikstudium Andere Studiengänge

Mathematik

Programmiersprachen

formaleSprachen

Computerlinguistik

Modellierung

SoftwareEngineering


Roadmap



What is a language?

© Oscar Nierstrasz


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Language = a set of sequences of symbols that we interpret to attribute meaning

Jack and Jill went up the hill …Jack and Jill went up the hill …

What is a formal language?

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A Turing machine reads (and writes) a tape of 0s and 1sA Turing machine reads (and writes) a tape of 0s and 1s

The language it accepts is the set of strings that leave it in an accepting stateThe language it accepts is the set of strings that leave it in an accepting state

How can we describe formal languages?

© Oscar Nierstrasz


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expression numberexpression expression + expression expression expression expressionnumber digitnumber digit number

expression numberexpression expression + expression expression expression expressionnumber digitnumber digit number

Use a set of rules ( ) to describe the structure of the languageUse a set of rules ( ) to describe the structure of the language

3 + 4 53 + 4 5

cf. Chomsky

What is a Programming Language? (take 1)

© Oscar Nierstrasz


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.-…-…-….-…---.---..-l.-..-.-. .-…-…-….-…---.---..-l.-..-.-.

.-…-…-….-…---.---..-l.-..-.-. .-…-…-….-…---.---..-l.-..-.-.

12368759752465426856875428654482654876578655123687597524654268568754286544826548765786551236875975246542685687542865448265487657865…

A language to instruct a computer to compute “stuff” …A language to instruct a computer to compute “stuff” …

But how does the computer interpret language?But how does the computer interpret language?


© Oscar Nierstrasz


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.-…-…-….-…---.---..-l.-..-.-. .-…-…-….-…---.---..-l.-..-.-.

.-…-…-….-…---.---..-l.-..-.-. .-…-…-….-…---.---..-l.-..-.-.

What the compiler will handle …What the compiler will handle …

0100100101100110010001110101011010000110101010100101111001111100010101000101011…

0100100101100110010001110101011010000110101010100101111001111100010101000101011…

But what about syntax and semantics?But what about syntax and semantics?

parse

analyze

transform optimizegenerate


© Oscar Nierstrasz


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.-…-…-….-…---.---..-l.-..-.-. .-…-…-….-…---.---..-l.-..-.-.

.-…-…-….-…---.---..-l.-..-.-. .-…-…-….-…---.---..-l.-..-.-.

Syntax and semantics in a mathematical domain …Syntax and semantics in a mathematical domain …

But what about the programmer?But what about the programmer?


© Oscar Nierstrasz


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A language for communicating software designsA language for communicating software designs


Roadmap



Over 8000 recorded programming languages

© Oscar Nierstrasz


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http://hopl.murdoch.edu.au/

Why so many?!Why so many?!

What do programming languages have in common?

© Oscar Nierstrasz


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# Compute factorialsdef fact(n) if n == 0 1 else n * fact(n-1) endend

puts fact(ARGV[0].to_i)

# Compute factorialsdef fact(n) if n == 0 1 else n * fact(n-1) endend

puts fact(ARGV[0].to_i)

commentscomments

keywordskeywords

functionsfunctionsvariablesvariables

control constructscontrol constructs

numbers, stringsnumbers, strings

expressionsexpressions

statementsstatements

A fragment of Ruby codeA fragment of Ruby code

Expressive power

© Oscar Nierstrasz


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Formally, all programming languages are equivalent …Formally, all programming languages are equivalent …

So what? …So what? …

Programming is modeling

© Oscar Nierstrasz


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How do these languages differ?

© Oscar Nierstrasz


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FunctionalFunctional

Object-orientedObject-orientedLogicLogic

ImperativeImperative


Roadmap



Jacquard loom — 1801

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Punch cards are inventedPunch cards are invented

Babbage’s Analytical Engine — 1822

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The first mechanical computerThe first mechanical computer

Church’s Lambda Calculus — 1932

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(λ x. (λ y. x)) a b(λ x. (λ y. x)) a b

The first (minimal) language for studying computationThe first (minimal) language for studying computation

(λ y. a) b (λ y. a) b

a a

if true then a else bif true then a else b

Turing machine — 1936

© Oscar Nierstrasz


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The first abstract model of a computer The first abstract model of a computer

1st generation: Machine code — 1944

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Machine code is only meant to be read by … machines

Machine code is only meant to be read by … machines

Subroutines — 1949

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The subroutine is one of the key concepts of programmingThe subroutine is one of the key concepts of programming

callcall

returnreturn

2nd generation: assembler — early 1950s

© Oscar Nierstrasz


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Assembly code introduces symbolic names (for humans!)Assembly code introduces symbolic names (for humans!)

3rd generation: FORTRAN — 1955

© Oscar Nierstrasz


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High-level languages are bornHigh-level languages are born

C AREA OF A TRIANGLE - HERON'S FORMULAC INPUT - CARD READER UNIT 5, INTEGER INPUTC OUTPUT - LINE PRINTER UNIT 6, REAL OUTPUTC INPUT ERROR DISPAY ERROR OUTPUT CODE 1 IN JOB CONTROL LISTING INTEGER A,B,C READ(5,501) A,B,C 501 FORMAT(3I5) IF(A.EQ.0 .OR. B.EQ.0 .OR. C.EQ.0) STOP 1 S = (A + B + C) / 2.0 AREA = SQRT( S * (S - A) * (S - B) * (S - C)) WRITE(6,601) A,B,C,AREA 601 FORMAT(4H A= ,I5,5H B= ,I5,5H C= ,I5,8H AREA= ,F10.2,12HSQUARE UNITS) STOP END

C AREA OF A TRIANGLE - HERON'S FORMULAC INPUT - CARD READER UNIT 5, INTEGER INPUTC OUTPUT - LINE PRINTER UNIT 6, REAL OUTPUTC INPUT ERROR DISPAY ERROR OUTPUT CODE 1 IN JOB CONTROL LISTING INTEGER A,B,C READ(5,501) A,B,C 501 FORMAT(3I5) IF(A.EQ.0 .OR. B.EQ.0 .OR. C.EQ.0) STOP 1 S = (A + B + C) / 2.0 AREA = SQRT( S * (S - A) * (S - B) * (S - C)) WRITE(6,601) A,B,C,AREA 601 FORMAT(4H A= ,I5,5H B= ,I5,5H C= ,I5,8H AREA= ,F10.2,12HSQUARE UNITS) STOP END

IF(A.EQ.0 .OR. B.EQ.0 .OR. C.EQ.0) STOP 1S = (A + B + C) / 2.0AREA = SQRT( S * (S - A) * (S - B) * (S - C))

ALGOL — 1958

© Oscar Nierstrasz


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begin...

end

begin...

end

Block structureBlock structure

<statement> ::= <unconditional statement>| <conditional statement>| <for statement>

...

<statement> ::= <unconditional statement>| <conditional statement>| <for statement>

...

BNFBNF

RecursionRecursion

Lisp — 1958

© Oscar Nierstrasz


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(defun factorial (n) (if (= n 1) 1 (* n (factorial (- n 1)))))

(defun factorial (n) (if (= n 1) 1 (* n (factorial (- n 1)))))

Programs as dataPrograms as data

Garbage collectionGarbage collection

COBOL — 1959

© Oscar Nierstrasz


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modulesmodules

ADD YEARS TO AGE.MULTIPLY PRICE BY QUANTITY GIVING COST.SUBTRACT DISCOUNT FROM COST GIVING FINAL-COST.

ADD YEARS TO AGE.MULTIPLY PRICE BY QUANTITY GIVING COST.SUBTRACT DISCOUNT FROM COST GIVING FINAL-COST.

10 INPUT "What is your name: ", U$20 PRINT "Hello "; U$30 INPUT "How many stars do you want: ", N40 S$ = ""50 FOR I = 1 TO N60 S$ = S$ + "*"70 NEXT I80 PRINT S$90 INPUT "Do you want more stars? ", A$100 IF LEN(A$) = 0 THEN GOTO 90110 A$ = LEFT$(A$, 1)120 IF A$ = "Y" OR A$ = "y" THEN GOTO 30130 PRINT "Goodbye "; U$140 END

10 INPUT "What is your name: ", U$20 PRINT "Hello "; U$30 INPUT "How many stars do you want: ", N40 S$ = ""50 FOR I = 1 TO N60 S$ = S$ + "*"70 NEXT I80 PRINT S$90 INPUT "Do you want more stars? ", A$100 IF LEN(A$) = 0 THEN GOTO 90110 A$ = LEFT$(A$, 1)120 IF A$ = "Y" OR A$ = "y" THEN GOTO 30130 PRINT "Goodbye "; U$140 END

BASIC — 1964

© Oscar Nierstrasz


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interactive programmingfor the masses

interactive programmingfor the masses

JCL — 1964

© Oscar Nierstrasz


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//IS198CPY JOB (IS198T30500),'COPY JOB',CLASS=L,MSGCLASS=X//COPY01 EXEC PGM=IEBGENER//SYSPRINT DD SYSOUT=*//SYSUT1 DD DSN=OLDFILE,DISP=SHR//SYSUT2 DD DSN=NEWFILE,// DISP=(NEW,CATLG,DELETE),// SPACE=(CYL,(40,5),RLSE),// DCB=(LRECL=115,BLKSIZE=1150)//SYSIN DD DUMMY

//IS198CPY JOB (IS198T30500),'COPY JOB',CLASS=L,MSGCLASS=X//COPY01 EXEC PGM=IEBGENER//SYSPRINT DD SYSOUT=*//SYSUT1 DD DSN=OLDFILE,DISP=SHR//SYSUT2 DD DSN=NEWFILE,// DISP=(NEW,CATLG,DELETE),// SPACE=(CYL,(40,5),RLSE),// DCB=(LRECL=115,BLKSIZE=1150)//SYSIN DD DUMMY

invented scripting for IBM 360invented scripting for IBM 360

Semaphores — 1965

© Oscar Nierstrasz


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P — acquire resource… critical sectionV — release resource

P — acquire resource… critical sectionV — release resource

radically simplified concurrency controlradically simplified concurrency control

Planner — 1969Prolog — 1972

© Oscar Nierstrasz


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man(socrates).mortal(X) :- man(X).man(socrates).mortal(X) :- man(X).

Facts and rulesFacts and rules

?- mortal(socrates).Yes?- mortal(socrates).Yes

Queries and inferencesQueries and inferences ?- mortal(elvis).No?- mortal(elvis).No

Pascal — 1970

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Supports structured programmingSupports structured programming

Successful with PCsSuccessful with PCs

function gcd (a, b: integer) : result real; var x : integer;begin if b= 0 then gcd := a else begin x := a; while (x >= b) do begin x := x - b end; gcd := gcd(b,x) endend

function gcd (a, b: integer) : result real; var x : integer;begin if b= 0 then gcd := a else begin x := a; while (x >= b) do begin x := x - b end; gcd := gcd(b,x) endend

begin

begin

end

endend

begin

C — 1972

© Oscar Nierstrasz


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Good for portable systems programmingGood for portable systems programming

Bridging low- and high-level programmingBridging low- and high-level programming

#include <stdio.h>//echo the command line argumentsint main (int argc, char* argv[]) {

int i;for (i=1; i<argc; i++) {

printf("%s ", argv[i]);}printf("\n");return 0;

}

#include <stdio.h>//echo the command line argumentsint main (int argc, char* argv[]) {

int i;for (i=1; i<argc; i++) {

printf("%s ", argv[i]);}printf("\n");return 0;

}

char*

i++

Smalltalk — 1972

© Oscar Nierstrasz


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Integer»factorialself = 0 ifTrue: [^ 1].self > 0 ifTrue: [^ self * (self - 1) factorial].self error: 'Not valid for negative integers'

Integer»factorialself = 0 ifTrue: [^ 1].self > 0 ifTrue: [^ self * (self - 1) factorial].self error: 'Not valid for negative integers'

5 factorial 1205 factorial 120

Everything is an objectEverything is an object

Everything happens by sending messagesEverything happens by sending messages

“Dynabook” vision“Dynabook” vision

self = 0 ifTrue: [^ 1]self > 0 ifTrue: [^ self * (self - 1) factorial].

ML polymorphic type inference — 1973

© Oscar Nierstrasz


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length [ ] = 0length (x:xs) = 1 + length xs

length :: [a] -> Int

length "hello" 5length [10..20] 11

length [ ] = 0length (x:xs) = 1 + length xs

length :: [a] -> Int

length "hello" 5length [10..20] 11

generic functions may be applied to many types of arguments

generic functions may be applied to many types of arguments

Monitors — 1974

© Oscar Nierstrasz


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structured concurrency controlstructured concurrency control

public class Account {protected int assets = 0;...public synchronized void withdraw(int amount) {

while (amount > assets) {try {

wait();} catch(InterruptedException e) { }

}assets -= amount;

}...

}

public class Account {protected int assets = 0;...public synchronized void withdraw(int amount) {

while (amount > assets) {try {

wait();} catch(InterruptedException e) { }

}assets -= amount;

}...

}

Bourne shell — 1977

© Oscar Nierstrasz


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cat Notes.txt| tr -c '[:alpha:]' '\012'| sed '/^$/d’| sort| uniq –c| sort –rn| head -5

cat Notes.txt| tr -c '[:alpha:]' '\012'| sed '/^$/d’| sort| uniq –c| sort –rn| head -5

Scripting pipelines of commands

Scripting pipelines of commands

14 programming14 languages 9 of 7 for 5 the

14 programming14 languages 9 of 7 for 5 the

SQL— 1978

© Oscar Nierstrasz


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SELECT * FROM BookWHERE price > 100.00ORDER BY title;

SELECT * FROM BookWHERE price > 100.00ORDER BY title;

Domain-specific language for relational databasesDomain-specific language for relational databases

Miranda — 1985

© Oscar Nierstrasz


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fibs = 1 : 1 : fibsAfter 1 1fibsAfter a b = (a+b) : fibsAfter b (a+b)fibs = 1 : 1 : fibsAfter 1 1fibsAfter a b = (a+b) : fibsAfter b (a+b)

Lazy evaluationLazy evaluation

take 10 fibs [1,1,2,3,5,8,13,21,34,55]take 10 fibs [1,1,2,3,5,8,13,21,34,55]

“Pure” functional programming“Pure” functional programming

Perl — 1987CGI — 1993

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Text manipulation, then web scriptingText manipulation, then web scripting

#!/usr/bin/perl -wprint "Content-type: text/html\n\n";print <<'eof'<html><head><title>Directory contents</title></head><body><h1>Directory contents</h1><ul>eof;@files = <*>;foreach $file (@files) {

print '<li><a href="' . $file . '">' . $file . "</li>\n";}print "</ul></body></html>\n";__END__

#!/usr/bin/perl -wprint "Content-type: text/html\n\n";print <<'eof'<html><head><title>Directory contents</title></head><body><h1>Directory contents</h1><ul>eof;@files = <*>;foreach $file (@files) {

print '<li><a href="' . $file . '">' . $file . "</li>\n";}print "</ul></body></html>\n";__END__

@files = <*>;foreach $file (@files) {

print '<li><a href="' . $file . '">' . $file . "</li>\n";}

JavaScript — 1995AJAX — 2005

© Oscar Nierstrasz


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Client-side browser scriptingClient-side browser scripting


Roadmap



Components, Frameworks, Patterns — 1990s

© Oscar Nierstrasz


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So far, limited impact on programming languages …So far, limited impact on programming languages …

Model-Driven Development — 1980s, 1990s

© Oscar Nierstrasz


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softwaredeveloper

PlatformIndependentModel

automatictranslation

Trends and Challenges

© Oscar Nierstrasz


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Bridging gap between users and technologyBridging gap between users and technologyyahoo pipesyahoo pipes

naked objectsnaked objects

subtextsubtext

graph transformationgraph transformation

Conclusions

© Oscar Nierstrasz


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Programming languages are for humans not just computersProgramming languages are for humans not just computers

Programming is modelingProgramming is modeling

Programming languages have always evolved to bring programming closer to the users’ problemsProgramming languages have always evolved to bring programming closer to the users’ problems

We are still very early in the history of programmingWe are still very early in the history of programming

Documents

Einführung in die Informatik 2. Programming Languages, Paradigms and Technology Institut für Informatik und angewandte Mathematik