Common Lisp Recipes: A Problem-Solution Approach

755 Pages·2015·8.04 MB·English

by  Edmund Weitz

®
BOOKS FOR PROFESSIONALS BY PROFESSIONALS
Weitz
Common Lisp Recipes
Common Lisp Recipes is a collection of solutions to problems and answers to questions you are
likely to encounter when writing real-world applications in Common Lisp. Written by an author who
has used Common Lisp in many successful commercial projects over more than a decade, this
book covers areas as diverse as web programming, databases, graphical user interfaces, integration
with other programming languages, multi-threading, and mobile devices as well as debugging
techniques and optimization, to name just a few. It is also the first Common Lisp book to tackle such
advanced topics as environment access, logical pathnames, Gray streams, delivery of executables,
pretty printing, setf expansions, or changing the syntax of Common Lisp.
The book is organized around specific problems or questions each followed by ready-to-use
example solutions and clear explanations of the concepts involved, plus pointers to alternatives
and more information. Each recipe can be read independently of the others and thus the book will
earn a special place on your bookshelf as a reference work you always want to have within reach.
Common Lisp Recipes is written in a style that mixes hands-on, no-frills pragmatism with precise
information and prudent mentorship.
(cid:127) Use Common Lisp’s object system (CLOS) and work with derived types, non-standard
method combinations, class changes on the fly, or the Metaobject Protocol (MOP)
(cid:127) Employ the Lisp reader and the Lisp printer and modify their behavior through readtables,
reader macros, and pretty print dispatch tables
(cid:127) Write robust code using Common Lisp’s condition system in combination with assertions,
handlers, and restarts
(cid:127) Call other languages like C, C++, or Java from Common Lisp, embed Common Lisp into other
languages, or deliver Common Lisp code as a binary or as a shared library
(cid:127) Develop and debug with steppers, inspectors, tracers, advices, and other tools
(cid:127) Optimize your code using techniques such as profilers, the disassembler, compiler hints,
declarations, stack allocation, memoization, inlining, special data structures, or compiler macros
ISBN 978-1-4842-1177-9
Shelve in: 56999
Programming Languages/General
User level:
Intermediate–Advanced
SOURCE CODE ONLINE 9781484211779
www.apress.com
Common Lisp Recipes
A Problem-Solution Approach
Edmund Weitz
CommonLispRecipes:AProblem-SolutionApproach
EdmundWeitz
Hamburg,Germany
ISBN-13(pbk):978-1-4842-1177-9 ISBN-13(electronic):978-1-4842-1176-2
DOI:10.1007/978-1-4842-1176-2
LibraryofCongressControlNumber:2015960959
Copyright©2016byEdmundWeitz
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ForHeikeandMouna
Table of Contents
AbouttheAuthor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . XVII
AbouttheTechnicalReviewer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . XIX
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . XXI
WhoThisBookIsFor . . . . . . . . . . . . . . . . . . . . . . . . XXI
WhoThisBookIs(Probably)NotFor . . . . . . . . . . . . . . XXII
HowtoReadThisBook . . . . . . . . . . . . . . . . . . . . . . XXII
What’sInandWhatNot . . . . . . . . . . . . . . . . . . . . . . XXIII
TheHyperSpec . . . . . . . . . . . . . . . . . . . . . . . . . . . XXIV
WhichImplementation . . . . . . . . . . . . . . . . . . . . . . XXIV
SourceCode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . XXV
TheIndex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . XXV
TypographicalConventions . . . . . . . . . . . . . . . . . . . . XXV
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . XXVI
1. SymbolsandPackages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1-1. UnderstandingtheRoleofPackagesandtheSymbolNomenclature . 1
1-2. MakingUniqueSymbols . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1-3. MakingSymbolsInaccessible . . . . . . . . . . . . . . . . . . . . . . . . 9
HowCanWeFixThis? . . . . . . . . . . . . . . . . . . . . . . . . 11
1-4. AvoidingNameConflicts . . . . . . . . . . . . . . . . . . . . . . . . . 12
WhenNameConflictsDoNotOccur . . . . . . . . . . . . . . . . 15
1-5. UsingSymbolsAsStand-InsforArbitraryForms . . . . . . . . . . . 15
1-6. SearchingforSymbolsbyName . . . . . . . . . . . . . . . . . . . . . 17
1-7. IteratingThroughAllSymbolsofaPackage . . . . . . . . . . . . . . 19
WhatToDoIfYouDon’tLikeLOOP. . . . . . . . . . . . . . . . . 20
1-8. Understanding COMMON LISP’sCase(In)Sensitivity . . . . . . . . . 21
StyleHint: Don’tUseCamelCase! . . . . . . . . . . . . . . . . . 25
1-9. UsingSymbolsAsStringSubstitutes. . . . . . . . . . . . . . . . . . . 26
So,WhatShouldYouUse?. . . . . . . . . . . . . . . . . . . . . . 27
1-10. “Overloading”ofStandard COMMON LISPOperators . . . . . . . . . 28
2. Conses,Lists,andTrees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2-1. UnderstandingConses . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
ListAccess . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
TestingWhetherSomethingIsaConsoraList . . . . . . . . . . 35
2-2. CreatingLists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
ConvertingVectorstoLists . . . . . . . . . . . . . . . . . . . . . 38
2-3. TransposingaMatrix. . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
V
TableofContents
2-4. UsingListInterpolation . . . . . . . . . . . . . . . . . . . . . . . . . . 40
2-5. AddingObjectstotheEndofaList . . . . . . . . . . . . . . . . . . . 42
TheTailWaggingtheList . . . . . . . . . . . . . . . . . . . . . . 44
2-6. “Splicing”intoaList . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
2-7. DetectingSharedStructureinLists . . . . . . . . . . . . . . . . . . . . 49
IsolatingtheNon-SharedPart . . . . . . . . . . . . . . . . . . . . 51
2-8. WorkingwithTrees. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
MoreComplicatedTrees . . . . . . . . . . . . . . . . . . . . . . . 54
COMMON LISP’sStandardTreeFunctions . . . . . . . . . . . . . 55
2-9. WorkingwithStacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
2-10. ImplementingaQueue . . . . . . . . . . . . . . . . . . . . . . . . . . 56
2-11. DestructuringandPatternMatching . . . . . . . . . . . . . . . . . . . 58
3. StringsandCharacters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
3-1. GettingtheASCIICodeofaCharacter . . . . . . . . . . . . . . . . . 61
TheOtherWayAround . . . . . . . . . . . . . . . . . . . . . . . 63
TheLimit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
3-2. NamingCharacters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
3-3. UsingDifferentCharacterEncodings . . . . . . . . . . . . . . . . . . 65
3-4. ComparingStringsorCharacters . . . . . . . . . . . . . . . . . . . . . 67
Internationalization . . . . . . . . . . . . . . . . . . . . . . . . . 70
3-5. EscapingCharactersinStringLiteralsandVariableInterpolation . . 71
IsItStillaLiteral?. . . . . . . . . . . . . . . . . . . . . . . . . . . 72
3-6. ControllingCase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
WhatAboutUnicode? . . . . . . . . . . . . . . . . . . . . . . . . 74
3-7. AccessingorModifyingaSubstring . . . . . . . . . . . . . . . . . . . 75
3-8. FindingaCharacteroraSubstringWithinaString . . . . . . . . . . 77
3-9. TrimmingStrings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
3-10. ProcessingaStringOneCharacterataTime . . . . . . . . . . . . . . 79
3-11. JoiningStrings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
3-12. ReadingCSVData . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
4. NumbersandMath . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
4-1. UsingArbitrarilyLargeIntegers . . . . . . . . . . . . . . . . . . . . . 87
4-2. UnderstandingFixnums . . . . . . . . . . . . . . . . . . . . . . . . . . 89
4-3. PerformingModularArithmetic . . . . . . . . . . . . . . . . . . . . . 92
EfficiencyConsiderations . . . . . . . . . . . . . . . . . . . . . . 93
4-4. SwitchingBases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
4-5. PerformingExactArithmeticwithRationalNumbers . . . . . . . . . 96
VariousWaysofConvertingNumberstoIntegers . . . . . . . . 98
HowNottoUseFLOORandFriends . . . . . . . . . . . . . . . . 99
ConvertingFloating-PointNumberstoRationalsandViceVersa 99
MixingRationalsandFloats . . . . . . . . . . . . . . . . . . . . . 101
4-6. ControllingtheDefaultFloatFormat . . . . . . . . . . . . . . . . . . 102
4-7. EmployingArbitraryPrecisionFloats . . . . . . . . . . . . . . . . . . 104
4-8. WorkingwithComplexNumbers . . . . . . . . . . . . . . . . . . . . 106
VI
TableofContents
4-9. ParsingNumbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
4-10. TestingWhetherTwoNumbersAreEqual . . . . . . . . . . . . . . . 111
Don’tEverUseEQwithNumbers! . . . . . . . . . . . . . . . . . 112
4-11. ComputingAnglesCorrectly . . . . . . . . . . . . . . . . . . . . . . . 113
4-12. CalculatingExactSquareRoots . . . . . . . . . . . . . . . . . . . . . . 115
5. ArraysandVectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
5-1. WorkingwithMultipleDimensions . . . . . . . . . . . . . . . . . . . 117
5-2. UnderstandingVectorsandSimpleArrays . . . . . . . . . . . . . . . 119
5-3. ObtainingtheSizeofanArray . . . . . . . . . . . . . . . . . . . . . . 120
5-4. ProvidingInitialContents . . . . . . . . . . . . . . . . . . . . . . . . . 121
AWarningAboutIdenticalObjects . . . . . . . . . . . . . . . . 122
5-5. TreatingArraysAsVectors . . . . . . . . . . . . . . . . . . . . . . . . 123
5-6. MakingtheLengthofVectorsFlexible . . . . . . . . . . . . . . . . . . 125
5-7. AdjustingArrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
5-8. UsinganArrayAsa“Window”intoAnotherArray. . . . . . . . . . 129
5-9. RestrictingtheElementTypeofanArray . . . . . . . . . . . . . . . . 131
UpgradingElementTypes . . . . . . . . . . . . . . . . . . . . . . 133
5-10. CopyinganArray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
AWarningAboutObjectIdentity. . . . . . . . . . . . . . . . . . 135
6. HashTables,Maps,andSets . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
6-1. UnderstandingtheBasicsofHashTables . . . . . . . . . . . . . . . . 137
WhyDoesGETHASHReturnTwoValues? . . . . . . . . . . . . . . 139
HowManyEntriesDoestheHashTableHave? . . . . . . . . . 140
6-2. ProvidingDefaultValuesForHashTableLookups . . . . . . . . . . 140
6-3. RemovingHashTableEntries . . . . . . . . . . . . . . . . . . . . . . . 142
6-4. IteratingThroughaHashTable . . . . . . . . . . . . . . . . . . . . . . 143
Don’tRelyonAnyOrder! . . . . . . . . . . . . . . . . . . . . . . 146
Don’tModifyWhileYou’reIterating! . . . . . . . . . . . . . . . 147
Can’tThisBeMoreConcise,Please? . . . . . . . . . . . . . . . . 147
6-5. UnderstandingHashTableTestsandDefiningYourOwn . . . . . . 148
WhatIsSXHASHFor? . . . . . . . . . . . . . . . . . . . . . . . . . 152
6-6. ControllingHashTableGrowth . . . . . . . . . . . . . . . . . . . . . 152
6-7. GettingRidofHashTableEntriesAutomatically. . . . . . . . . . . . 155
6-8. RepresentingMapsAsAssociationLists . . . . . . . . . . . . . . . . 158
CombiningLookupandManipulation . . . . . . . . . . . . . . . 161
WhyWouldAnybodyPreferAlistsoverHashTables? . . . . . 162
6-9. RepresentingMapsAsPropertyLists . . . . . . . . . . . . . . . . . . 163
WhentoPreferPlistsoverAlists . . . . . . . . . . . . . . . . . . 165
ThePlistofaSymbol . . . . . . . . . . . . . . . . . . . . . . . . . 166
6-10. WorkingwithSets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
RepresentingSetsAsHashTables . . . . . . . . . . . . . . . . . 169
RepresentingSetsAsBitPatterns . . . . . . . . . . . . . . . . . . 169
7. SequencesandIteration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
7-1. FilteringaSequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
VII
TableofContents
7-2. SearchingaSequence . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
7-3. SortingandMergingSequences . . . . . . . . . . . . . . . . . . . . . 175
7-4. MixingDifferentSequenceTypes . . . . . . . . . . . . . . . . . . . . . 177
7-5. Re-UsingaPartofaSequence . . . . . . . . . . . . . . . . . . . . . . 177
7-6. RepeatingSomeValuesCyclically . . . . . . . . . . . . . . . . . . . . 179
Alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
7-7. CountingDown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
7-8. Iteratingover“Chunks”ofaList . . . . . . . . . . . . . . . . . . . . . 184
7-9. ClosingoverIterationVariables . . . . . . . . . . . . . . . . . . . . . 186
7-10. “Extending”ShortSequencesinIterations . . . . . . . . . . . . . . . 187
7-11. BreakingoutofLOOP . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
7-12. MakingSenseoftheMAP... Zoo . . . . . . . . . . . . . . . . . . . . . 191
TheSequenceVariants . . . . . . . . . . . . . . . . . . . . . . . . 194
7-13. DefiningYourOwnSequenceTypes . . . . . . . . . . . . . . . . . . . 194
7-14. IteratingwithITERATE . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
7-15. IteratingwithSERIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
WhattheExampleDoes . . . . . . . . . . . . . . . . . . . . . . . 201
8. TheLispReader. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
8-1. EmployingtheLispReaderforYourOwnCode . . . . . . . . . . . . 203
WhyREADIsPotentiallyDangerous . . . . . . . . . . . . . . . . 205
WhatREADDoesn’tDo . . . . . . . . . . . . . . . . . . . . . . . . 205
TheOptionalArgumentstoREAD . . . . . . . . . . . . . . . . . . 206
GoWild! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
8-2. TroubleshootingLiteralObjectNotation . . . . . . . . . . . . . . . . . 206
ThisAlsoAppliestoStrings! . . . . . . . . . . . . . . . . . . . . 208
8-3. EvaluatingFormsatReadTime . . . . . . . . . . . . . . . . . . . . . 208
WhattoLookOutFor . . . . . . . . . . . . . . . . . . . . . . . . 210
Alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
8-4. EmbeddingLiteralArraysintoYourCode . . . . . . . . . . . . . . . 211
TheUsualWarning . . . . . . . . . . . . . . . . . . . . . . . . . . 212
8-5. UnderstandingtheDifferentWaystoRefertoaFunction . . . . . . . 213
8-6. RepeatingSomethingYouAlreadyTyped . . . . . . . . . . . . . . . . 214
TheyDon’tOnlyLookIdentical,TheyAreIdentical! . . . . . . . 216
8-7. SafelyExperimentingwithReadtables . . . . . . . . . . . . . . . . . . 216
TemporarilySwitchingtoStandardIOSyntax . . . . . . . . . . 218
8-8. ChangingtheSyntaxTypeofaCharacter . . . . . . . . . . . . . . . . 219
TheSixSyntaxTypes . . . . . . . . . . . . . . . . . . . . . . . . . 220
HowtoActuallyChangetheSyntaxType . . . . . . . . . . . . . 222
SomeThingsNeverChange . . . . . . . . . . . . . . . . . . . . . 222
8-9. CreatingYourOwnReaderMacros . . . . . . . . . . . . . . . . . . . 223
WhatReaderMacroFunctionsDo . . . . . . . . . . . . . . . . . 224
8-10. WorkingwithDispatchingMacroCharacters . . . . . . . . . . . . . . 226
8-11. PreservingWhitespace . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
VIII
TableofContents
9. Printing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
9-1. UsingthePrintingPrimitives . . . . . . . . . . . . . . . . . . . . . . . 231
PrintingObjectsSoThatTheyCanBeReadBackinAgain . . . 235
Shortcuts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
9-2. PrintingtoandintoStrings . . . . . . . . . . . . . . . . . . . . . . . . 237
9-3. PrintingNILAsaList . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
9-4. ExtendingFORMATControlStringsOverMoreThanOneLine . . . . 240
9-5. UsingFunctionsAsFORMATControls . . . . . . . . . . . . . . . . . . . 241
9-6. CreatingYourOwnFORMATDirectives . . . . . . . . . . . . . . . . . . 243
9-7. RecursiveProcessingofFORMATControls . . . . . . . . . . . . . . . . 245
9-8. ControllingHowYourOwnObjectsArePrinted . . . . . . . . . . . . 247
9-9. ControllingthePrettyPrinter . . . . . . . . . . . . . . . . . . . . . . . 249
9-10. PrintingLongLists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
9-11. Pretty-PrintingCompoundObjects . . . . . . . . . . . . . . . . . . . 257
UsingthePrettyPrinterfromFORMAT . . . . . . . . . . . . . . . 260
9-12. ModifyingthePrettyPrinter . . . . . . . . . . . . . . . . . . . . . . . 262
10. Evaluation,Compilation,ControlFlow . . . . . . . . . . . . . . . . . . . . . 265
10-1. ComparingArbitraryLispObjects . . . . . . . . . . . . . . . . . . . . 265
ComparingState . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
Constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
10-2. UsingConstantVariablesasKeysinCASEMacros . . . . . . . . . . . 269
10-3. UsingArbitraryVariableNamesforKeywordParameters . . . . . . 271
KeywordNamesDon’tHavetoBeKeywords . . . . . . . . . . 272
KeywordDamesDon’tHavetoBeConstant . . . . . . . . . . . 273
10-4. Creating“StaticLocalVariables,”Likein C . . . . . . . . . . . . . . . 273
10-5. “Preponing”theComputationofValues . . . . . . . . . . . . . . . . 275
10-6. ModifyingtheBehaviorofFunctionsYouDon’tHavetheSourceOf 278
10-7. SwappingtheValuesofVariables(orPlaces) . . . . . . . . . . . . . . 280
10-8. CreatingYourOwnUpdateFormsfor“Places” . . . . . . . . . . . . 283
UsingDEFSETF . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
UsingDEFINE-SETF-EXPANDER . . . . . . . . . . . . . . . . . . . 286
So,WhichOneDoIUse? . . . . . . . . . . . . . . . . . . . . . . 291
UsingDEFINE-MODIFY-MACRO . . . . . . . . . . . . . . . . . . . . 291
Multiple-ValuedPlaces . . . . . . . . . . . . . . . . . . . . . . . 293
10-9. WorkingwithEnvironments . . . . . . . . . . . . . . . . . . . . . . . 294
10-10. CommentingOutPartsofYourCode . . . . . . . . . . . . . . . . . . 299
SomeNotesAbout;and#| . . . . . . . . . . . . . . . . . . . . . 302
How;,#|,andOthersAreImplemented . . . . . . . . . . . . . 302
11. Concurrency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303
11-1. ManagingLispProcesses . . . . . . . . . . . . . . . . . . . . . . . . . 304
EscapeHatches . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307
ThreadsAreExpensive . . . . . . . . . . . . . . . . . . . . . . . 308
11-2. AccessingSharedResourcesConcurrently . . . . . . . . . . . . . . . 308
Locks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312
IX
TableofContents
AtomicOperations . . . . . . . . . . . . . . . . . . . . . . . . . . 313
MoreProblems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314
11-3. UsingSpecialVariablesinConcurrentPrograms . . . . . . . . . . . . 317
Per-ThreadInitialBindings . . . . . . . . . . . . . . . . . . . . . 319
VariablesThatAreAlwaysGlobal . . . . . . . . . . . . . . . . . 319
11-4. CommunicatingwithOtherThreads . . . . . . . . . . . . . . . . . . . 320
Alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322
11-5. ParallelizingAlgorithmsWithoutThreadsandLocks . . . . . . . . . 322
WhattheExampleDoes . . . . . . . . . . . . . . . . . . . . . . . 325
Fine-Tuning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326
Ptrees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326
Alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330
11-6. DeterminingtheNumberofCores . . . . . . . . . . . . . . . . . . . . 330
12. ErrorHandlingandAvoidance . . . . . . . . . . . . . . . . . . . . . . . . . . 333
12-1. CheckingTypesatRunTime . . . . . . . . . . . . . . . . . . . . . . . 333
Alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
12-2. AddingAssertionstoYourCode . . . . . . . . . . . . . . . . . . . . . 336
DisablingAssertionsin“ProductionCode” . . . . . . . . . . . . 338
12-3. DefiningYourOwnConditions . . . . . . . . . . . . . . . . . . . . . . 338
HowConditionsArePrinted . . . . . . . . . . . . . . . . . . . . 340
12-4. SignalingaCondition . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
ConditionDesignators . . . . . . . . . . . . . . . . . . . . . . . . 343
12-5. HandlingConditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . 344
IgnoringErrors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349
12-6. ProvidingandUsingRestarts . . . . . . . . . . . . . . . . . . . . . . . 350
VisibleRestarts . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354
PredefinedRestarts . . . . . . . . . . . . . . . . . . . . . . . . . . 355
12-7. GettingRidofWarningMessages . . . . . . . . . . . . . . . . . . . . 356
12-8. ProtectingCodefromNon-LocalExits . . . . . . . . . . . . . . . . . . 357
“WITH-”Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360
13. Objects,Classes,Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
13-1. DefiningTypes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
CompoundTypeSpecifiers . . . . . . . . . . . . . . . . . . . . . 363
DerivedTypes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365
13-2. UsingClassesAsTypes . . . . . . . . . . . . . . . . . . . . . . . . . . 366
13-3. WritingMethodsforBuilt-InClasses . . . . . . . . . . . . . . . . . . 367
13-4. ProvidingConstructorsforYourClasses . . . . . . . . . . . . . . . . 369
13-5. MarkingSlotsAs“Private” . . . . . . . . . . . . . . . . . . . . . . . . 372
13-6. ChangingtheArgumentPrecedenceOrder . . . . . . . . . . . . . . . 374
13-7. AutomaticallyInitializingSlotsonFirstUsage . . . . . . . . . . . . . 376
13-8. ChangingandRedefiningClassesontheFly . . . . . . . . . . . . . . 377
ObjectsChangingTheirClass . . . . . . . . . . . . . . . . . . . . 380
RedefiningClasses . . . . . . . . . . . . . . . . . . . . . . . . . . 381
13-9. MakingYourObjectsExternalizable . . . . . . . . . . . . . . . . . . . 383
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