programming concept-sebesta

8/18/2019 programming concept-sebesta

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ISBN 0-321-49362-1

Chapter 1

Preliminaries


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Copyright © 2009 Addison-Wesley. All rights reserved. 1-2

Chapter 1 Topics

• Reasons for Studying Concepts ofProgramming Languages

• Programming Domains

• Language Evaluation Criteria

• Inuences on Language Design

• Language Categories

• Language Design Trade!"#s• Implementation $ethods

• Programming Environments


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Reasons for Studying Conceptsof Programming Languages

• Increased a%ility to e&press ideas

• Improved %ac'ground for choosingappropriate languages

• Increased a%ility to learn ne( languages

• )etter understanding of signi*cance ofimplementation

• )etter use of languages that are already'no(n

• "verall advancement of computing


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Programming Domains

• Scienti*c applications+ Large num%ers of oating point computations, use of arrays+ -ortran

• )usiness applications+ Produce reports. use decimal num%ers and characters+ C")"L

• /rti*cial intelligence+ Sym%ols rather than num%ers manipulated, use of lin'ed

lists+ LISP

• Systems programming+ 0eed eciency %ecause of continuous use+ C

• 2e% Soft(are+ Eclectic collection of languages3 mar'up 4e5g5. 67T$L8.

scripting 4e5g5. P7P8. general!purpose 4e5g5. 9ava8


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Language Evaluation Criteria

• Readability3 the ease (ith (hichprograms can %e read and understood

• Writability3 the ease (ith (hich a

language can %e used to createprograms

• Reliability3 conformance tospeci*cations 4i5e5. performs to its

speci*cations8• Cost3 the ultimate total cost


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Evaluation Criteria3 Reada%ility

•"verall simplicity+ / managea%le set of features and constructs+ $inimal feature multiplicity+ $inimal operator overloading

• "rthogonality+ / relatively small set of primitive constructs can %e com%ined in a

relatively small num%er of (ays

+ Every possi%le com%ination is legal• Data types

+ /de:uate prede*ned data types

• Synta& considerations+ Identi*er forms3 e&i%le composition+ Special (ords and methods of forming compound statements

+ -orm and meaning3 self!descriptive constructs. meaningful 'ey(ords


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Evaluation Criteria3 2rita%ility

• Simplicity and orthogonality+ -e( constructs. a small num%er of primitives. a small set of

rules for com%ining them

• Support for a%straction

+ The a%ility to de*ne and use comple& structures oroperations in (ays that allo( details to %e ignored

• E&pressivity

+ / set of relatively convenient (ays of specifying operations

+ Strength and num%er of operators and prede*nedfunctions


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Evaluation Criteria3 Relia%ility

• Type chec'ing+ Testing for type errors

• E&ception handling+ Intercept run!time errors and ta'e corrective measures

• /liasing+ Presence of t(o or more distinct referencing methods for the

same memory location

• Reada%ility and (rita%ility+ / language that does not support ;natural< (ays of e&pressing

an algorithm (ill re:uire the use of ;unnatural< approaches.and hence reduced relia%ility


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Evaluation Criteria3 Cost

• Training programmers to use thelanguage

• 2riting programs 4closeness to particularapplications8

• Compiling programs• E&ecuting programs

• Language implementation system3

availa%ility of free compilers• Relia%ility3 poor relia%ility leads to highcosts

• $aintaining programs


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Evaluation Criteria3 "thers

• Porta%ility

+ The ease (ith (hich programs can %e movedfrom one implementation to another

• =enerality+ The applica%ility to a (ide range of

applications

• 2ell!de*nedness

+ The completeness and precision of thelanguage>s ocial de*nition


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Inuences on Language Design

• Computer /rchitecture+ Languages are developed around the

prevalent computer architecture. 'no(n as thevon Neumann architecture

• Programming $ethodologies+ 0e( soft(are development methodologies

4e5g5. o%?ect!oriented soft(are development8led to ne( programming paradigms and %y

e&tension. ne( programming languages


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Computer /rchitecture Inuence

• 2ell!'no(n computer architecture3 @on 0eumann

• Imperative languages. most dominant. %ecauseof von 0eumann computers+ Data and programs stored in memory

+ $emory is separate from CPA

+ Instructions and data are piped from memory to CPA

+ )asis for imperative languages

• @aria%les model memory cells

• /ssignment statements model piping• Iteration is ecient


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The von 0eumann /rchitecture


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The von 0eumann /rchitecture

• -etch!e&ecute!cycle 4on a von 0eumannarchitecture computer8

initialize the program counterrepeat forever

fetch the instruction pointed by the counter

increment the counter

decode the instruction

execute the instruction

end repeat


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Programming $ethodologiesInuences

• 1Bs and early 1Bs3 Simple applications,(orry a%out machine eciency

• Late 1Bs3 People eciency %ecame important,reada%ility. %etter control structures

+ structured programming+ top!do(n design and step!(ise re*nement

• Late 1BFs3 Process!oriented to data!oriented+ data a%straction

• $iddle 1BGs3 "%?ect!oriented programming+ Data a%straction H inheritance H polymorphism


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Language Categories

• Imperative+ Central features are varia%les. assignment statements. and

iteration+ Include languages that support o%?ect!oriented programming+ Include scripting languages+ Include the visual languages

+ E&amples3 C. 9ava. Perl. 9avaScript. @isual )/SIC 50ET. CHH• -unctional+ $ain means of ma'ing computations is %y applying functions to

given parameters+ E&amples3 LISP. Scheme

• Logic

+ Rule!%ased 4rules are speci*ed in no particular order8+ E&ample3 Prolog

• $ar'upprogramming hy%rid+ $ar'up languages e&tended to support some programming+ E&amples3 9STL. 6SLT


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Language Design Trade!"#s

• Relia%ility vs5 cost of e&ecution+ E&ample3 9ava demands all references to array elements

%e chec'ed for proper inde&ing. (hich leads toincreased e&ecution costs

• Reada%ility vs5 (rita%ilityE&ample3 /PL provides many po(erful operators 4and a

large num%er of ne( sym%ols8. allo(ing comple&computations to %e (ritten in a compact program %ut atthe cost of poor reada%ility

• 2rita%ility 4e&i%ility8 vs5 relia%ility+ E&ample3 CHH pointers are po(erful and very e&i%le

%ut are unrelia%le


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Implementation $ethods

• Compilation+ Programs are translated into machine language

• Pure Interpretation

+ Programs are interpreted %y another program 'no(n asan interpreter

• 7y%rid Implementation Systems

+ / compromise %et(een compilers and pure interpreters


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Layered @ie( of Computer

The operating systemand languageimplementation arelayered overmachine interface of acomputer


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Compilation

• Translate high!level program 4source language8into machine code 4machine language8

• Slo( translation. fast e&ecution

• Compilation process has several phases3

+ le&ical analysis3 converts characters in the sourceprogram into le&ical units

+ synta& analysis3 transforms le&ical units into parse trees(hich represent the syntactic structure of program

+ Semantics analysis3 generate intermediate code

+ code generation3 machine code is generated


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The Compilation Process


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/dditional Compilation Terminologies

• Load module 4e&ecuta%le image83 theuser and system code together

• Linking and loading3 the process of

collecting system program units andlin'ing them to a user program


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@on 0eumann )ottlenec'

• Connection speed %et(een a computer>smemory and its processor determines thespeed of a computer

• Program instructions often can %ee&ecuted much faster than the speed ofthe connection, the connection speed thusresults in a bottleneck

• Jno(n as the von Neumann bottleneck , itis the primary limiting factor in the speedof computers


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Pure Interpretation

• 0o translation• Easier implementation of programs 4run!time

errors can easily and immediately %e displayed8

• Slo(er e&ecution 41 to 1 times slo(er than

compiled programs8• "ften re:uires more space

• 0o( rare for traditional high!level languages

• Signi*cant come%ac' (ith some 2e% scriptinglanguages 4e5g5. 9avaScript. P7P8


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Pure Interpretation Process


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7y%rid Implementation Systems

• / compromise %et(een compilers and pureinterpreters

• / high!level language program is translatedto an intermediate language that allo(s easy

interpretation• -aster than pure interpretation

• E&amples+ Perl programs are partially compiled to detect errors %efore

interpretation

+ Initial implementations of 9ava (ere hy%rid, the intermediateform. byte code. provides porta%ility to any machine thathas a %yte code interpreter and a run!time system4together. these are called Java Virtual Machine8


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7y%rid Implementation Process


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9ust!in!Time Implementation Systems

• Initially translate programs to an intermediatelanguage

• Then compile the intermediate language of thesu%programs into machine code (hen they arecalled

• $achine code version is 'ept for su%se:uent calls

• 9IT systems are (idely used for 9ava programs

• 50ET languages are implemented (ith a 9ITsystem


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Preprocessors

• Preprocessor macros 4instructions8 arecommonly used to specify that code fromanother *le is to %e included

• / preprocessor processes a programimmediately %efore the program iscompiled to e&pand em%eddedpreprocessor macros

• / (ell!'no(n e&ample3 C preprocessor+ e&pands #include, #define. and similar

macros


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Programming Environments

• / collection of tools used in soft(aredevelopment

• A0I6+ /n older operating system and tool collection

+ 0o(adays often used through a =AI 4e5g5. CDE. JDE. or=0"$E8 that runs on top of A0I6

• $icrosoft @isual Studio50ET+ / large. comple& visual environment

• Ased to %uild 2e% applications and non!2e% applications in

any 50ET language

• 0et)eans+ Related to @isual Studio 50ET. e&cept for 2e%

applications in 9ava


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Copyright © 2009 Addison Wesley All rights reserved 1 31

Summary

• The study of programming languages is valua%lefor a num%er of reasons3+ Increase our capacity to use di#erent constructs+ Ena%le us to choose languages more intelligently+ $a'es learning ne( languages easier

• $ost important criteria for evaluatingprogramming languages include3+ Reada%ility. (rita%ility. relia%ility. cost

• $a?or inuences on language design have %eenmachine architecture and soft(are developmentmethodologies

• The ma?or methods of implementing programminglanguages are3 compilation. pure interpretation.and hy%rid implementation

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