YACC(1)                                                   YACC(1)

     NAME
          yacc - yet another compiler-compiler

     SYNOPSIS
          yacc [ option ... ] grammar

     DESCRIPTION
          Yacc converts a context-free grammar and translation code
          into a set of tables for an LR(1) parser and translator.
          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'.  This program must be loaded
          with a lexical analyzer function, yylex(void) (often gener-
          ated by lex(1)), with a main(int argc, char *argv[]) pro-
          gram, and with an error handling routine, yyerror(char*).

          The options are

          -o output  Direct output to the specified file instead of
                     y.tab.c.

          -Dn        Create file y.debug, containing diagnostic mes-
                     sages.  To incorporate them in the parser, com-
                     pile it with preprocessor symbol yydebug defined.
                     The amount of diagnostic output from the parser
                     is regulated by value n. The value 0 reports
                     errors; 1 reports reductions; higher values (up
                     to 4) include more information about state tran-
                     sitions.

          -v         Create file y.output, containing a description of
                     the parsing tables and of conflicts arising from
                     ambiguities in the grammar.

          -d         Create file y.tab.h, containing #define state-
                     ments that associate yacc-assigned `token codes'
                     with user-declared `token names'.  Include it in
                     source files other than y.tab.c to give access to
                     the token codes.

          -s stem    Change the prefix `y' of the file names y.tab.c,
                     y.tab.h, y.debug, and y.output to stem.

          -S         Write a parser that uses Stdio instead of the
                     print routines in libc.

          -l         Disable #line directives in the generated parser.

     YACC(1)                                                   YACC(1)

          -a         Generate a parser that takes an argument of type
                     Yyarg and passes this argument to each invocation
                     of the lexer function, yylex.  Yyarg contains
                     per-instance state and a single user-visible mem-
                     ber, arg, of type void*.

          The specification of yacc itself is essentially the same as
          the UNIX version described in the references mentioned
          below.  Besides the -D option, the main relevant differences
          are:

               The interface to the C environment is by default
               through <libc.h> rather than <stdio.h>; the -S option
               reverses this.

               The parser accepts UTF input text (see utf(7)), which
               has a couple of effects.  First, the return value of
               yylex() no longer fits in a short; second, the starting
               value for non-terminals is now 0xE000 rather than 257.

               The generated parser can be recursive: actions can call
               yyparse, for example to implement a sort of #include
               statement in an interpreter.

               Finally, some undocumented inner workings of the parser
               have been changed, which may affect programs that know
               too much about its structure.

     FILES
          y.output
          y.tab.c
          y.tab.h
          y.debug
          y.tmp.*        temporary file
          y.acts.*       temporary file
          /lib/yaccpar   parser prototype
          /lib/yaccpars  parser prototype using stdio

     SOURCE
          /src/cmd/yacc.c

     SEE ALSO
          lex(1)
          S. C. Johnson and R. Sethi, ``Yacc: A parser generator'',
          Unix Research System Programmer's Manual, Tenth Edition,
          Volume 2
          B. W. Kernighan and Rob Pike, The UNIX Programming Environ-
          ment, Prentice Hall, 1984

     BUGS
          The parser may not have full information when it writes to
          y.debug so that the names of the tokens returned by `yylex'

     YACC(1)                                                   YACC(1)

          may be missing.