Whatissyntaxanalysis Specicationofprogramminglanguagescontextfreegrammars Parsingcontextfreelanguagespushdownautomata TopdownparsingLL1andrecursivedescentparsing BottomupparsingLRparsin ID: 441649
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OutlineoftheLecture Whatissyntaxanalysis? Specicationofprogramminglanguages:context-freegrammars Parsingcontext-freelanguages:push-downautomata Top-downparsing:LL(1)andrecursive-descentparsing Bottom-upparsing:LR-parsing Y.N.Srikant Parsing Derivations E)E!E+EE+E)E!idid+E)E!idid+idisaderivationoftheterminalstringid+idfromE Inaderivation,aproductionisappliedateachstep,toreplaceanonterminalbytheright-handsideofthecorrespondingproduction Intheaboveexample,theproductionsE!E+E,E!id,andE!id,areappliedatsteps1,2,and,3respectively Theabovederivationisrepresentedinshortas,E)id+id,andisreadasSderivesid+id Y.N.Srikant Parsing DerivationTrees Derivationscanbedisplayedastrees Theinternalnodesofthetreeareallnonterminalsandtheleavesareallterminals CorrespondingtoeachinternalnodeA,thereexistsaproduction2P,withtheRHSoftheproductionbeingthelistofchildrenofA,readfromlefttoright Theyieldofaderivationtreeisthelistofthelabelsofalltheleavesreadfromlefttoright If istheyieldofsomederivationtreeforagrammarG,thenS) andconversely Y.N.Srikant Parsing DerivationTreeExample Y.N.Srikant Parsing LeftmostandRightmostDerivations:AnExample Y.N.Srikant Parsing EquivalentUnambiguousGrammar Y.N.Srikant Parsing AmbiguityExample2(contd.) Y.N.Srikant Parsing FragmentofC-Grammar(Statements) program�--VOIDMAIN'('')'compound_stmtcompound_stmt�--'{''}'|'{'stmt_list'}'|'{'declaration_liststmt_list'}'stmt_list�--stmt|stmt_liststmtstmt�--compound_stmt|expression_stmt|if_stmt|while_stmtexpression_stmt�--';'|expression';'if_stmt�--IF'('expression')'stmt|IF'('expression')'stmtELSEstmtwhile_stmt�--WHILE'('expression')'stmtexpression�--assignment_expr|expression','assignment_expr Y.N.Srikant Parsing FragmentofC-Grammar(ExpressionsandDeclarations) relational_expr�--add_expr|relational_expr'add_expr|relational_expr&#x'-60;�''add_expr|relational_exprLE_OPadd_expr|relational_exprGE_OPadd_expradd_expr&#x'-60;�--mult_expr|add_expr'+'mult_expr|add_expr'-'mult_exprmult_expr&#x'-60;�--unary_expr|mult_expr'*'unary_expr|mult_expr'/'unary_exprdeclarationlist&#x'-60;�--declaration|declarationlistdeclarationdeclaration&#x'-60;�--typeidlist';'idlist&#x'-60;�--idlist','ID|IDtype&#x'-60;�--INT_TYPE|FLOAT_TYPE|CHAR_TYPE Y.N.Srikant Parsing PDA-Examples L=f0n1njn0gM=(fq0;q1;q2;q3g;f0;1g;fZ;0g;;q0;Z;fq0g),whereisdenedasfollows(q0;0;Z)=f(q1;0Z)g,(q1;0;0)=f(q1;00)g,(q1;1;0)=f(q2;)g,(q2;1;0)=f(q2;)g,(q2;;Z)=f(q0;)g (q0;0011;Z)`(q1;011;0Z)`(q1;11;00Z)`(q2;1;0Z)`(q2;;Z)`(q0;;) (q0;001;Z)`(q1;01;0Z)`(q1;1;00Z)`(q2;;0Z)`error (q0;010;Z)`(q1;10;0Z)`(q2;0;Z)`error Y.N.Srikant Parsing