Steps in Scala

506 Pages·2010·12.248 MB·English

by  Loverdos C. K. K., Syropoulos A.

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STEPS IN SCALA
AnIntroductiontoObject-FunctionalProgramming
Object-functionalprogrammingisalreadyhere.Scalaisthemostprominentrep-
resentativeofthisexcitingapproachtoprogramming,bothinthesmallandinthe
large. In this book we show how Scala proves to be a highly expressive, concise,
and scalable language, which grows with the needs of the programmer, whether
professionalorhobbyist.
Readthebooktoseehowto:
• leveragethefullpoweroftheindustry-provenJVMtechnologywithalanguagethatcould
havecomefromthefuture;
• learn Scala step-by-step, following our complete introduction and then dive into spe-
ciallychosendesignchallengesandimplementationproblems,inspiredbythereal-world,
softwareengineeringbattlefield;
• embracethepowerofstatictypingandautomatictypeinference;
• usethedualobjectandfunctionalorientednaturescombinedatScala’score,toseehow
towritecodethatisless“boilerplate”andtowitnessarealincreaseinproductivity.
Use Scala for fun, for professional projects, for research ideas. We guarantee the
experiencewillberewarding.
Christos K. K. Loverdos is a research inclined computer software profes-
sional.HeholdsaB.Sc.andanM.Sc.inComputerScience.Hehasbeenworking
inthesoftwareindustryformorethantenyears,designingandimplementingflex-
ible,enterprise-levelsystemsandmakingstrategictechnicaldecisions.Hehasalso
publishedresearchpapersontopicsincludingdigitaltypography,service-oriented
architectures,and highly available distributed systems. Last but not least,he is an
advocateofopensourcesoftware.
Apostolos Syropoulos is a computer scientist. He holds a B.Sc. in Physics,
anM.Sc.inComputerScience,andaPh.D.inTheoreticalComputerScience.His
researchinterestsfocusoncomputabilitytheory,categorytheory,fuzzysettheory,
and digital typography. He has authored or co-authored six books,was co-editor
ofamulti-authorvolume,andhaspublishedmorethan50papersandarticles.

STEPS IN SCALA
An Introduction to Object-Functional Programming
CHRISTOS K. K. LOVERDOS
APOSTOLOS SYROPOULOS
CAMBRIDGE UNIVERSITY PRESS
Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore,
São Paulo, Delhi, Dubai, Tokyo
Cambridge University Press
The Edinburgh Building, Cambridge CB2 8RU, UK
Published in the United States of America by Cambridge University Press, New York
www.cambridge.org
Information on this title: www.cambridge.org/9780521762175
© C. K. K. Loverdos and A. Syropoulos 2010
This publication is in copyright. Subject to statutory exception and to the
provision of relevant collective licensing agreements, no reproduction of any part
may take place without the written permission of Cambridge University Press.
First published in print format 2010
ISBN-13 978-0-511-90054-9 eBook (EBL)
ISBN-13 978-0-521-76217-5 Hardback
ISBN-13 978-0-521-74758-5 Paperback
Cambridge University Press has no responsibility for the persistence or accuracy
of urls for external or third-party internet websites referred to in this publication,
and does not guarantee that any content on such websites is, or will remain,
accurate or appropriate.
ToKaterina,whoisalwayshereandisconstantlymakingmeabetterperson
CKKL
(cid:1)τoυς γovε´ις µoυ (cid:3)εω´ργιo και Bασιλικη´ και στov
γιo µoυ (cid:5)ηµη´τριo-(cid:3)εω´ ργιo
AS

Contents
Preface page xiii
1 Introduction 1
1.1 Objectorientation 1
1.2 Anoverviewoffunctionalprogramming 7
1.3 Extendablelanguages 9
1.4 Scala:beyondtheJavaprogramminglanguage 14
2 Corefeatures 16
2.1 “HelloWorld!”inScala 16
2.2 Scala’sbasictypes 18
2.3 Classesandobjects 24
2.4 Somebasicoperators 29
2.5 Basicbuilt-incontrolstructures 32
2.6 Subclassesandinheritance 38
2.7 Functions 42
2.8 Arraysandtuples 48
2.9 Commandlinearguments 53
2.10 Sets 56
2.11 Hashtables 59
2.12 Memofunctions 62
2.13 Lists 64
2.14 Strings 74
2.15 Regularexpressions 76
2.16 ScientificcomputationwithScala 84
2.17 Innerclasses 87
2.18 Packages 88
2.19 Documentationcomments 90
2.20 Annotations 92
vii
viii Contents
3 Advancedfeatures 95
3.1 Playingwithtrees 95
3.2 Moreaboutpatternmatching 103
3.2.1 Typesofpatterns 103
3.2.2 Sealedclasses 107
3.2.3 Optionalvalues 108
3.3 Traitsandmix-incomposition 109
3.4 Sortingobjects 116
3.5 Moreonfunctions 118
3.6 Polymorphism 125
3.6.1 Typesofpolymorphism 125
3.6.2 Overloading 127
3.6.3 Implicitconversion:aformofcoercion 128
3.6.4 Parametricpolymorphism 131
3.6.5 Moreonimplicitparameters 136
3.6.6 Inclusionpolymorphism 137
3.6.7 Covariance,contravarianceandinvariance 138
3.6.8 Boundedpolymorphism 140
3.6.9 Viewsandviewbounds 143
3.6.10 Existentialtypes 144
3.6.11 Typeprojections 147
3.6.12 Typeerasure 147
3.7 Nominalandstructuraltyping 148
∗
3.8 Higherorderpolymorphism 150
3.9 Streamsare“infinite”lists! 156
∗
3.10 Moreonmemofunctions 158
3.11 Assertions 159
3.12 Settersandgetters 161
∗
3.13 Monads 163
4 Parserbuilders 171
4.1 Languageparsers 171
4.2 Scala’sparserbuilders 174
4.3 Aninterpreterforatoylanguage 177
4.4 Domain-specificlanguages 184
4.5 Monadicparsing 185
5 XMLprocessing 187
5.1 WhatisXML? 187
5.2 BasicXMLcontentmanipulation 189
5.3 ProducingXHTMLcontentwithScala 193
5.4 XMLinputandoutput 196