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.