lecture 5: syntax analysis - computer sciencestotts/comp144/lectures/lect5.pdfparsing • parsing an...

COMP 144Programming Language ConceptsLecture 5: Syntax Analysis

January 18, 2002

Felix Hernandez-Campos 1

COMP 144 Programming Language ConceptsFelix Hernandez-Campos

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Lecture 5: Lecture 5: Syntax AnalysisSyntax Analysis

COMP 144 Programming Language ConceptsCOMP 144 Programming Language ConceptsSpring 2002Spring 2002

Felix HernandezFelix Hernandez--CamposCampos

Jan 18Jan 18

The University of North Carolina at Chapel HillThe University of North Carolina at Chapel Hill


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Review: Compilation/InterpretationReview: Compilation/Interpretation

Compiler or InterpreterCompiler or Interpreter

Translation Translation ExecutionExecution

Source CodeSource Code

Target CodeTarget Code

InterpreInterpre--tationtation


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Review: Syntax AnalysisReview: Syntax Analysis



Source CodeSource Code•• Specifying the Specifying the formform

of a programming of a programming

languagelanguage

–– TokensTokens»» Regular Regular

ExpressionExpression

–– SyntaxSyntax»» ContextContext--FreeFree

GrammarsGrammarsTarget CodeTarget Code


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Phases of CompilationPhases of Compilation


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Syntax AnalysisSyntax Analysis

•• Syntax:Syntax:–– Webster’s definition: Webster’s definition: 1 a : the way in which linguistic 1 a : the way in which linguistic

elements (as words) are put together to form constituents elements (as words) are put together to form constituents (as phrases or clauses)(as phrases or clauses)

•• The syntax of a programming languageThe syntax of a programming language–– Describes its formDescribes its form

»» Organization of tokensOrganization of tokens (elements)(elements)»» Context Free Grammars (CFGs)Context Free Grammars (CFGs)

–– Must be Must be recognizablerecognizable by compilers and interpretersby compilers and interpreters»» ParsingParsing»» LL and LR parsersLL and LR parsers


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Context Free GrammarsContext Free Grammars

•• CFGsCFGs–– Add recursion to regular expressionsAdd recursion to regular expressions

»» Nested constructionsNested constructions–– NotationNotation

expressionexpression →→ identifieridentifier | | numbernumber | | -- expressionexpression| | (( expressionexpression ))| | expressionexpression operatoroperator expressionexpression

operator operator →→ ++ | | -- | | ** | | //

»» Terminal symbolsTerminal symbols»» NonNon--terminal symbolsterminal symbols»» Production rule (i.e. substitution rule)Production rule (i.e. substitution rule)

terminal symbol terminal symbol →→ terminal and nonterminal and non--terminal symbolsterminal symbols


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ParsersParsers

•• ScannersScanners–– Task: recognize language tokensTask: recognize language tokens–– Implementation: Deterministic Finite AutomatonImplementation: Deterministic Finite Automaton

»» Transition based on the next characterTransition based on the next character

•• ParsersParsers–– Task: recognize language syntax (organization of tokens)Task: recognize language syntax (organization of tokens)–– Implementation:Implementation:

»» TopTop--down parsingdown parsing»» BottomBottom--up parsingup parsing


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Parse TreesParse Trees

•• A parse is graphical representation of a derivationA parse is graphical representation of a derivation•• ExampleExample


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Parsing exampleParsing example

•• Example: commaExample: comma--separated list of identifierseparated list of identifier

–– CFGCFG

id_list id_list →→ idid id_list_tailid_list_tailid_list_tail id_list_tail →→ ,, id_list_tailid_list_tailid_list_tail id_list_tail →→ ;;

–– ParsingParsing

A, B, C;A, B, C;


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TopTop--down derivation of down derivation of A, B, C;A, B, C;

CFGCFG

LeftLeft--toto--right,right,LeftLeft--most derivationmost derivation

LL(1) parsingLL(1) parsing


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TopTop--down derivation of down derivation of A, B, C;A, B, C;

CFGCFG


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BottomBottom--up parsing of up parsing of A, B, C;A, B, C;

CFGCFG

LeftLeft--toto--right,right,RightRight--most derivationmost derivation

LR(1) parsingLR(1) parsing


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CFGCFG


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CFGCFG


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ParsingParsing

•• Parsing an arbitrary Context Free GrammarParsing an arbitrary Context Free Grammar–– O(nO(n33))–– Too slow for large programsToo slow for large programs

•• LinearLinear--time parsingtime parsing–– LL parsers LL parsers

»» Recognize LL grammarRecognize LL grammar»» Use a topUse a top--down strategydown strategy

–– LR parsersLR parsers»» Recognize LR grammarRecognize LR grammar»» Use a bottomUse a bottom--up strategyup strategy


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Hierarchy of Linear ParsersHierarchy of Linear Parsers

•• Basic containment relationshipBasic containment relationship–– All CFGs can be recognized by LR parserAll CFGs can be recognized by LR parser–– Only a subset of all the CFGs can be recognized by LL Only a subset of all the CFGs can be recognized by LL

parsersparsers

LL parsingLL parsing

CFGsCFGs LR parsingLR parsing


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Recursive Descent Parser ExampleRecursive Descent Parser Example

•• LL(1) grammarLL(1) grammar


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•• Outline of Outline of

recursive parserrecursive parser

–– This parser onlyThis parser onlyverifies syntaxverifies syntax

–– matchmatch isisthe scannerthe scanner


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2020



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Semantic AnalysisSemantic Analysis



Source CodeSource Code•• Specifying the Specifying the meaningmeaning

of a programming of a programming

languagelanguage

–– Attribute GrammarsAttribute Grammars

Target CodeTarget Code


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Reading AssignmentReading Assignment

•• Scott’s Chapter 2Scott’s Chapter 2–– Section 2.2.2Section 2.2.2–– Section 2.2.3Section 2.2.3

lecture 5: syntax analysis - computer sciencestotts/comp144/lectures/lect5.pdfparsing • parsing an...

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