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PROGRAM:

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 This
program must be loaded with a lexical analyzer function, yylex(void) (often generated by
lex(1)), with a main(int argc, char *argv[]) program, 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 messages. To incorporate them in
the parser, compile 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 transitions.

-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 statements 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 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.

-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 member, 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.

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