YACC(1)                                                   YACC(1)

     NAME
          yacc, eyacc - yet another compiler-compiler

     SYNOPSIS
          yacc [ -vdD ] [ -o output ] [ -s stem ] grammar

          eyacc [ -v ] [ grammar ]

     DESCRIPTION
          Yacc converts a context-free grammar into a set of tables
          for a simple automaton which executes an LR(1) parsing algo-
          rithm.  The grammar may be ambiguous; specified precedence
          rules are used to break ambiguities.

          The output file, y.tab.c, must be compiled by the C compiler
          to produce a program yyparse. The output file name can be
          set with the -o flag.  This program must be loaded with the
          lexical analyzer program, yylex, as well as main and
          yyerror, an error handling routine.  These routines must be
          supplied by the user; lex(1) is useful for creating lexical
          analyzers usable by yacc.

          If the -D flag is given, yacc creates y.debug, which con-
          tains default error messages for the parser.  The parser
          will use them if it is compiled with the preprocessor symbol
          YYDEBUG defined.  The amount of diagnostic output is con-
          trolled by an external variable yydebug. If it is 2, the
          parser prints out the name of each token returned by yylex
          and each reduction.  If it is 1, the parser prints out the
          reductions, and if it is 0, the parser only reports errors.

          If the -v flag is given, the file y.output is prepared,
          which contains a description of the parsing tables and a
          report on conflicts generated by ambiguities in the grammar.

          If the -d flag is used, the file y.tab.h is generated with
          the define statements that associate the yacc-assigned
          `token codes' with the user-declared `token names'.  This
          allows source files other than y.tab.c to access the token
          codes.

          The prefix y. for the files y.tab.c y.tab.h, y.debug, and
          y.output can be changed to stem by the -s flag.

          Eyacc is an old version of yacc, with systematic error
          recovery.  It is used in pascal(1).

     FILES
          y.output
          y.tab.c

     YACC(1)                                                   YACC(1)

          y.tab.h       defines for token names
          y.debug
          y.tmp.??????  temporary file
          y.acts.?????  temporary file
          /usr/lib/yaccparparser prototype for C programs
          /lib/liby.a   library with default `main' and `yyerror'

     SEE ALSO
          lex(1)
          LR Parsing by A. V. Aho and S. C. Johnson, Computing Sur-
          veys, June, 1974.
          YACC - Yet Another Compiler Compiler by S. C. Johnson.
          Susan L. Graham, Charles B. Haley, and W. N. Joy, Practical
          LR Error Recovery, SIGPLAN Conference on Compiler Construc-
          tion, August, 1979.

     DIAGNOSTICS
          The number of reduce-reduce and shift-reduce conflicts is
          reported on the standard output; a more detailed report is
          found in the y.output file.  Similarly, if some rules are
          not reachable from the start symbol, this is also reported.

     BUGS
          The parser may not have full information when it prints out
          y.debug so that the names of the tokens returned by yylex
          may be missing.