There are significantdifferences between the processing of the left hand symboland an ordinary shift of a token, however, so this action iscalled a goto action. A new state is obtained,pushed onto the stack, and parsing continues. Using thisuncovered state, and the symbol on the left side of the rule,perform what is in effect a shift of A. After poppingthese states, a state is uncovered which was the state the parserwas in before beginning to process the rule.

In effect,these states were the ones put on the stack while recognizing x,y, and z, and no longer serve any useful purpose. To reduce, first pop off the top three states fromthe stack (In general, the number of states popped equals thenumber of symbols on the right side of the rule). The reduce action depends on the left hand symbol (A in thiscase), and the number of symbols on the right hand side (three inthis case). Appendix C gives an exampleusing some of the more advanced features of Yacc, and, finally,Appendix D describes mechanisms and syntax no longer activelysupported, but provided for historical continuity with older versionsof Yacc. Section 10discusses some advanced topics, and Section 11 gives acknowledgements.Appendix A has a brief example, and Appendix B gives asummary of the Yacc input syntax. Section 9 gives some suggestions which should improvethe style and efficiency of the specifications. Section 8 discusses theoperating environment and special features of the parsers Yaccproduces. Section 7discusses error detection and recovery. Section 6 describes a simple mechanism for handlingoperator precedences in arithmetic expressions. Section 5 discusses various reasons why Yaccmay be unable to produce a parser from a specification, and whatto do about it. Section 4 describes the operationof the parser. The next several sections describe the basic process ofpreparing a Yacc specification Section 1 describes the preparationof grammar rules, Section 2 the preparation of the user suppliedactions associated with these rules, and Section 3 thepreparation of lexical analyzers.

Online execution ex and yacc compiler