term% cat index.txt YACC(1) General Commands Manual 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 algorithm. 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 an‐
alyzers usable by yacc.
If the -D flag is given, yacc creates y.debug, which contains default
error messages for the parser. The parser will use them if it is com‐
piled with the preprocessor symbol YYDEBUG defined. The amount of di‐
agnostic output is controlled 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
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 Surveys, 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 Construction, 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 sym‐
bol, 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.
YACC(1)