NAME

yacc − yet another compiler-compiler

SYNOPSIS

yacc [ −vVdlt ] [ −Q [ y|n ]] filename

DESCRIPTION

The yacc command converts a context-free grammar into a set of tables for a simple automaton that executes an LALR(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 function 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; the lex(1) command is useful for creating lexical analyzers usable by yacc. 

−v Prepares the file y.output, which contains a description of the parsing tables and a report on conflicts generated by ambiguities in the grammar. 

−d Generates the file y.tab.h with the #define statements that associate the yacc -assigned “token codes” with the user-declared “token names.” This association allows source files other than y.tab.c to access the token codes. 

−l Specifies that the code produced in y.tab.c will not contain any #line constructs.  This option should only be used after the grammar and the associated actions are fully debugged. 

-Q[y|n] The −Qy option puts the version stamping information in y.tab.c.  This allows you to know what version of yacc built the file.  The −Qn option (the default) writes no version information. 

−t Compiles runtime debugging code by default.  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.  Whether or not the −t option is used, the runtime debugging code is under the control of YYDEBUG, a preprocessor 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. 

−V Prints on the standard error output the version information for yacc. 

ENVIRONMENT

The environment variables LC_CTYPE and LANG control the character classification throughout yacc.  On entry to yacc, these environment variables are checked in the following order: LC_CTYPE and LANG.  When a valid value is found, remaining environment variables for character classification are ignored.  For example, a new setting for LANG does not override the current valid character classification rules of LC_CTYPE.  When none of the values is valid, the shell character classification defaults to the POSIX.1 C locale. 

yacc can handle characters from EUC primary and supplementary codesets as one-token symbols.  EUC codes may only be single character quoted terminal symbols.  yacc expects yylex () to return a wide character (wchar_t) value for these one-token symbols. 

FILES

y.output

y.tab.c

y.tab.h defines for token names

yacc.tmp,

yacc.debug, yacc.acts temporary files

yaccpar parser prototype for C programs

SEE ALSO

lex(1)

The yacc chapter in the SunOS 5.1 Programming Utilities manual. 

DIAGNOSTICS

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 instance is also reported. 

NOTES

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

SunOS 5.1  —  Last change: 5 Mar 1992