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Yacc Examples

Yacc Examples. 66.648 Compiler Design Lecture (01/28/98) Computer Science Rensselaer Polytechnic. Lecture Outline. YACC program format Examples - These are in the course home page under Pgms/yaccpgms. YACC program format. It Consists of three parts as in the case of lex.

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Yacc Examples

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  1. Yacc Examples • 66.648 Compiler Design Lecture (01/28/98) • Computer Science • Rensselaer Polytechnic

  2. Lecture Outline • YACC program format • Examples - These are in the course home page under Pgms/yaccpgms

  3. YACC program format • It Consists of three parts as in the case of lex. • 1. Declarations • 2. Productions • 3. Programs

  4. Format • %{ • /* Parser Specs */ • #include ... • #define … • %} • %token STDK • %token STRING • %start Program

  5. Format Cont... • %% • Program: PROGRAMTK.. • ; • stmts: stmts stmt • | • ; • … • %%

  6. Format Cont... • %% • void yyerror(char *) { …} • void main(void) • { yyparse(); • }

  7. Declaration Section • Any C initialization that may be necessary for the parser’s interface with the rest of the system. • The specification of various language categories • or tokens. (Sometime certain precednces). • The specification of the left hand side of a particular production as the start symbol.

  8. Productions • This part is a specification of the grammar in LALR(1) of whatever we want to parse. • For your first project, the grammar will be that of Java. • It is essentail that the grammar is of LALR(1) - free of ambiguities - Otherwise, you will get error messages such as shift-reduce conflicts and/or reduce/reduce conflicts.

  9. Supporting Program Section • This is a third major part of the parser specification file. This optional section may contain a number of supporting C functions or compiler directives to include a file containing these functions. • The function yyerror(), that allows the user to specify action taken by the parser when a finite state machine enters an error state. • The parse alos requires that a scanner yylex() be provided. So, if you don’t use lex, you have to provide such a function.

  10. Compiling YACC Programs • yacc -d -v parser.y • (-d produces y.tab.h defining tokens as integer numbers. • -v produces y.output, the complete finite state machine description. -v can be omitted most often unless you are debugging the grammar itself. ) • This produces y.tab.c file. • To compile, • gcc y.tab.c -ll -ly • -ll and -ly are lex and yacc libraries.

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