Lecture 1. Topics. Principles of programming languages (2007) Lecture 1. What makes programming languages such an interesting subject?

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1 Priciples of programmig laguages (2007) Lecture 1 Natalia Silvis-Cividjia silvis@few.vu.l Lecture 1. Topics Studet survey Itroductio History of major programmig laguages About this course vrije Uiversiteit amsterdam Which programmig laguages do you kow? Very well : A little: Just heard about: Which laguage is your favourite? What laguages you fid iterestig or you would like to lear? What is the first high-level programmig laguage ad whe did it appear? Whe did Java appear ad for what purposes? Ca you give a defiitio of the followig cocepts? If yes give a example. Aoymous fuctio Coercio Polymorphism Automatic garbage collectio Strog/weak type checkig What is : Pytho Ruby Eiffel Self Explai to a layma what is OOP ad why is it so importat? What do you expect from this course? What makes programmig laguages such a iterestig subject? The amazig variety The amazig variety The odd cotroversies The itriguig evolutio 1

2 The amazig variety There are very may, very differet laguages (ca 2500) Ofte grouped ito four families: Imperative Fuctioal Logic Object-orieted Imperative Laguages Visual laguages Example: a factorial fuctio i C Subcategory of imperative laguages it fact(it ) { it sofar = 1; while (>0) sofar *= --; retur sofar; Visual Basic Oce called fourth-geeratio laguages Hallmarks : Assigmet Iteratio Order of executio is critical Object-Orieted Laguages Object-Orieted Laguages Example: a Java object public class MyIt { private it value; public MyIt(it value) { this.value = value; public it getvalue() { retur value; public MyIt getfact() { retur ew MyIt(fact(value)); private it fact(it ) { it sofar = 1; while ( > 1) sofar *= --; retur sofar; Hallmarks : Usually imperative, plus Costructs to help programmers use objects little budles of data that kow how to do thigs to themselves 2

3 Fuctioal Laguages Aother Fuctioal Laguage Example: a factorial fuctio i ML Example: a factorial fuctio i Lisp fu fact x = if x <= 0 the 1 else x * fact(x-1); (defu fact (x) (if (<= x 0) 1 (* x (fact (- x 1))))) Hallmarks : No assigmet, o side effects Heavy use of recursio: o iteratios Looks very differet from ML But ML ad Lisp are closely related Logic Laguages Example: a factorial fuctio i Prolog fact(x,1) :- X =:= 1. fact(x,fact) :- X > 1, NewX is X - 1, fact(newx,nf), Fact is X * NF. Hallmark : Program expressed as rules i formal logic The amazig variety The odd cotroversies The Odd Cotroversies Programmig laguages are the subject of may heated debates: Partisa argumets Laguage stadards Fudametal defiitios The best programmig laguage Java Fortra Cobol C C++ PHP Javascript C# ML Prolog? 3

4 No clear wier Laguage Partisas Obviously, there is o best laguage for all situatios. The best laguage might deped o may thigs: Type of program Reaso the program is built Size of program Programmer familiarity Time available Cost Legacy There is a lot of argumet about the relative merits of differet laguages Every laguage has partisas, who praise it i extreme terms ad defed it agaist all detractors To experiece some of this, explore ewsgroups: comp.lag.* Evaluatio Criteria Evaluatio criteria Readability Writability Reliability Programmig domais Laguage Stadards Scietific applicatios Busiess applicatios Artificial itelligece Scriptig laguages Systems programmig Iteret ad Web The documets that defie laguage stadards are ofte drafted by iteratioal committees Ca be a slow ad complicated process Fortra 82 8X stadard released i

5 Basic Defiitios Some terms refer to fuzzy cocepts: all those laguage family ames, for example No problem; just remember they are fuzzy Bad: Is X really a object-orieted laguage? Good: What aspects of X support a object-orieted style of programmig? The amazig variety The odd cotroversies The itriguig evolutio History of major programmig laguages A updated geealogical diagram ca be foud at Read Ch.2 Sebesta, ch. 24 Weber [from Sebesta] Plakalkül (1945) Plakalkül (Korad Zuse) = calculus for a computig pla a high level laguage to express computatios o computer Z4 Has: q Machie idepedet operatios, assigmet statemets, q floatig poit data types, records, expressios with parethesis, q coditioal statemets but o else, repetitio of statemets, subrouties q algorithms from array sortig to playig chess o 60 pages 5

6 Plakalkül But A + 1 => A V 4 5 S Difficult otatio Z4 had a memory of 64 words of 32 bits each Never implemeted Published vary late i 1972 Itermediate steps Fortra (1954) Machie code Poor readability Difficult to modify No hardware with floatig poit arithmetic, o idexig Pseudocode FORTRAN = mathematical FORmula TRANslatig System first compiled high level laguage IBM 704 system has floatig poit istructios i hardware Promised the efficiecy of machie code ad the ease of programmig of pseudocodes. Almost succeeded. Code was very fast. Most of the calculatios were umeric. Computers were more expesive tha programmers, so o dyamic storage C FORTRAN PROGRAM TO FIND MEAN OF N NUMBERS AND C NUMBER OF VALUES GREATER THAN THE MEAN DIMENSION A(99) REAL MEAN READ(1,5)N 5 FORMAT(I2) READ(1,10) (A(I),I=1,N) 10 FORMAT(6F10.5) SUM= SUM=SUM+A(I) MEAN=SUM/FLOAT(N) NUMBER=0 DO 20 I=1,N IF (A(I).LE.MEAN) GOTO 20 NUMBER=NUMBER+1 20 CONTINUE WRITE(2,25) MEAN,NUMBER 25 FORMAT(8H MEAN=,F10.5,5X,20H NUMBER OVER MEAN =,I5) STOP END A Fortra program [from R. Clarck, Comparative programmig Laguages] First step to sofisticatio: ALGOL 58 ad ALGOL 60 Situatio: Laguages were developed aroud sigle architecture IBM or UNIVAC, commuicatio was difficult. No uiversal laguage No portable laguage I 1958 ACM (USA) + GAMM (EUR) came together to discuss the desig of oe iteratioal laguage compromises about spheres of ifluece. Goals: Close to mathematical otatios Good for describig algorithms Must be traslatable to machie code 6

7 ALGOL 58 features Cocept of type Names have ay legth Compoud statemets Semicolo as separator Assigmet operator as := Else-if clause But: abadoed by IBM. ALGOL 60 New features: block structure, pass by value ad pass by ame, subprogram recursio Success: stadard way to publish algorithms for 20 years All imperative laguages are based o it. First machie idepedet laguage First laguage whose sytax was formally defied by BNF grammar Failure: Never widely used i USA, lack of support from IBM (Fortra compilers were faster), o I/O, formal sytax descriptio begi ed commet this program fids the mea of umbers ad the umber of values greater tha the mea ; iteger ; read (); begi real array a[1:]; iteger i, umber; real sum,mea; for i:=1 step 1 util do read (a[i]); sum : =0.0; for i:=1 step 1 util do sum := sum + a[i]; mea := sum / ; umber := 0 ; for i := 1 step 1 util do if a[i] > mea the umber := umber + 1; write ("MEAN=",mea, "NUMBER OVER MEAN =", umber) ed A ALGOL program [from R. Clarck, Comparative programmig Laguages] COBOL (1959) First laguage required by DoD Must look like simple Eglish (maagers ca read code). Still the most widely used busiess applicatios laguage. 7

8 Time sharig: BASIC (1964) BASIC Easy to lear ad use by o-sciece (liberal arts) studets Supposed to be a liberal arts programmig laguage First widely used with time sharig (termials istead of puch cards) 10 REM THIS IS A BASIC PROGRAM FOR FINDING THE MEAN 20 DIM A(99) 30 INPUT N 40 FOR I=1 TO N 50 INPUT A(I) 60 LET S=S+A(I) 70 NEXT I 80 LET M=S/N 90 LET K=0 100 FOR I=1 TO N 110 IF A(I) < M THEN LET K=K NEXT I 140 PRINT "MEAN IS", MEAN 150 PRINT "NUMBER GREATER THAN MEAN IS",K 160 STOP 170 END Everythig for everybody: PL/I A BASIC program [from R. Clarck, Comparative programmig Laguages] PL/I Developed by IBM Built as a laguage for both kids of applicatios: scietific computig ad busiess First amed Fortra VI, the NPL, PL/I Has:poiters, cocurrecy, recursivity, error hadlig Nowadays early dead laguage: too complicated Usig PL/I must be like flyig a plae with 7,000 buttos, switches, ad hadles to maipulate i the cockpit. (Edsger Dijkstra) 8

9 Data abstractio: SIMULA 67 SIMULA 67 Based o ALGOL 60 for system simulatios (Norway) Cotributios: corouties A structure called class Classes are base for data abstractio Classes iclude data ad fuctioality Objects ad iheritace Orthogoal desig: ALGOL68 Descedats of ALGOL:Pascal Descedats of ALGOL:C Largest desig effort: Ada

10 ADA Object-orieted : Smalltalk 1980 Huge effort, much moey, hudreds of people, DoD support (Hoeywell/Bull) Cotributios: Packages for data abstractio Exceptios hadlig Geeric programmig uits Cocurrecy But: too large ad complex, Compilers very difficult to build, the role of C++ Combiig imperative with OO: C++ Imperative based OO laguage: Java What makes a laguage successful? What makes a laguage successful? Expressive power Ease of use for a ovice Ease of implemetatio Ope source Excellet compilers Ecoomics, patroage ad iertia 10

11 About this course Adam Brooks Weber, Moder Programmig Laguages. About this course 1. A study of the scriptig laguage Pytho based o all the fudametal cocepts discussed i Weber s book. 2. A o-goig assigmet: to explore ad report o a less familiar laguage (see website for the details about this assigmet). About this course Other recommeded books: R. Sebesta, Cocepts of programmig laguages, 2005 M. Scott, Programmig laguage pragmatics, 2005 R. Clarck, Comparative Programmig Laguages, 2001 Week Date 7 september 14 September 28 September Lecture topic Itroductio. History of programmig laguages evolutio Sytax ad sematics Laguage systems Fuctioal programmig: ML 1 Types Fuctioal programmig: ML 2 Polymorphism Fuctioal programmig: ML 3 Scope Memory maagemet Object orieted programmig: Java 1 Logic programmig: Prolog Scriptig laguages: Pytho 1 Scriptig laguages: Pytho 2 Presetatio sessio Guests lectures Aims! " # $ %%&# $ &$' # $ # (# ") * %%&# +,- $./ # 0 1$(32 4/56 * # # %/ % $ # ) 7 * * 8 9%0/ * ( # ) *& / # "! 9 $5: $ 3+ 4/4 & % "$ 5. / / # /$ # &% /4$") + Questios? 11