.TH YACC 1 
.SH NAME
yacc, eyacc \- yet another compiler-compiler
.SH SYNOPSIS
.B yacc
[
.B \-vdD
]
[
.B \-o
output
]
[
.B \-s
stem
]
grammar
.PP
.B eyacc 
[
.B \-v
] [ grammar ]
.SH DESCRIPTION
.I yacc
converts a context-free grammar into a set of
tables for a simple automaton which executes an LR(1) parsing
algorithm.
The grammar may be ambiguous;
specified precedence rules are used to break ambiguities.
.PP
The output file,
.IR y.tab.c ,
must be compiled by the C compiler
to produce a program
.IR yyparse .
The output file name can be set with the
.B \-o
flag.
This program must be loaded with the lexical analyzer program,
.IR yylex ,
as well as
.I main
and
.IR yyerror ,
an error handling routine.
These routines must be supplied by the user;
.IR lex (1)
is useful for creating lexical analyzers usable by
.IR yacc .
.PP
If the
.B \-D
flag is given,
.I yacc
creates
.IR y.debug ,
which contains default error messages for the parser.
The parser will use them if it is compiled with the preprocessor symbol
.I YYDEBUG
defined.
The amount of diagnostic output is controlled by an external variable
.IR yydebug .
If it is 2, the parser prints out the name of each token returned by
.I yylex
and each reduction.
If it is 1, the parser prints out the reductions, and if it is 0,
the parser only reports errors.
.PP
If the
.B \-v
flag is given, the file
.I y.output
is prepared, which contains a description of the parsing tables
and a report on
conflicts generated by ambiguities in the grammar.
.PP
If the \-\fBd\fR flag is used, the file
.I y.tab.h
is generated with the
.I define
statements that associate the
.I yacc\c
-assigned `token codes' with the user-declared `token names'.
This allows source files other than
.I y.tab.c
to access the token codes.
.PP
The prefix
.I y.
for the files
.I y.tab.c
.IR y.tab.h ,
.IR y.debug ,
and
.I y.output
can be changed to
.I stem
by the
.B \-s
flag.
.PP
.I eyacc
is an old version of
.I yacc,
with systematic error recovery.
It is used in
.IR pascal (1).
.SH FILES
.ta \w'y.acts.?????? 'u
y.output
.br
y.tab.c
.br
y.tab.h	defines for token names
.br
y.debug
.br
y.tmp.??????	temporary file
.br
y.acts.?????	temporary file
.br
/usr/lib/yaccpar	parser prototype for C programs
.br
/lib/liby.a	library with default `main' and `yyerror'
.SH "SEE ALSO"
.IR lex (1)
.br
.I "LR Parsing"
by A. V. Aho and S. C. Johnson,
Computing Surveys, June, 1974.
.br
.I "YACC \- Yet Another Compiler Compiler"
by S. C. Johnson.
.br
Susan L. Graham, Charles B. Haley, and W. N. Joy,
.I "Practical LR Error Recovery,"
SIGPLAN Conference on Compiler Construction,
August, 1979.
.SH DIAGNOSTICS
The number of reduce-reduce and shift-reduce conflicts
is reported on the standard output;
a more detailed report is
found in the
.I y.output
file.
Similarly, if some rules are not reachable from the
start symbol, this is also reported.
.SH BUGS
The parser may not have full information when it prints out
.I y.debug
so that the names of the tokens returned by
.I yylex
may be missing.