NAME

yacc − yet another compiler-compiler

SYNOPSIS

yacc [ −vdlt ] [ −N<secondary><n> ... ] 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. 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 −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. 

If the −l flag is given, the code produced in y.tab.c will not contain any #line constructs.  Generally, this should only be used after y.tab.c has compiled successfully, since the #line directives allow the C compiler to give error messages that refer to the yacc source file rather than the y.tab.c file.  This option is useful, however, for symbolic debugging, since some symbolic debuggers may be confused by line numbers that are not in order. 

The −N<secondary><n> option allows the sizes of certain internal yacc tables to be reset.  Secondary is one of the letters from the set { a m s p n e c l w } and specifies the table; n is the new size.  Tables that can be reset by using secondary letters are as follows:

a a-array size; default is 12000.

m mem array size; default is 12000.

s number of states; default is 1000. 

p number of productions; default is 800. 

n number of non-terminals; default is 600. 

e temp-space size; default is 1250. 

c name-space size; default is 5000. 

l look-ahead set table size; default is 650. 

w working set table size; default is 650. 

If an array overflows, yacc issues a fatal error message including a suggestion of which table to reset.  For example:

too many states, try −Ns option

Runtime debugging code is always generated in y.tab.c under conditional compilation control.  By default, this code is not included when y.tab.c is compiled.  However, when yacc’s −t option is used, this debugging code will be compiled by default.  Independent of whether the −t option was used, the runtime debugging code is under the control of YYDEBUG, a pre-processor symbol.  If YYDEBUG has a non-zero value, then the debugging code is included.  If its value is zero, then the code will not be included.  The size and execution time of a program produced without the runtime debugging code will be smaller and slightly faster. 

ERRORS

The number of reduce-reduce and shift-reduce conflicts is reported on the standard error 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. 

FILES

y.output

y.tab.c

y.tab.h defines for token names

yacc.tmp,

yacc.acts, yacc.debug temporary files

/usr/lib/yaccpar parser prototype for C programs

WARNINGS

Because file names are fixed, at most one yacc process can be active in a given directory at a time. 

The maximum number of terminal symbols is fixed at 2000 and cannot be reset using the −N option. 

SEE ALSO

lex(1), malloc(3X).  LR Parsing by A. V. Aho and S. C. Johnson, Computing Surveys, June, 1974.  YACC − Yet Another Compiler Compiler in HP-UX Concepts and Tutorials. 

INTERNATIONAL SUPPORT

8-bit data and filenames. 

Hewlett-Packard Company  —  Version B.1,  April 12, 1993