NAME

yacc − yet another compiler-compiler

SYNOPSIS

yacc [ −vdlt ] grammar

DESCRIPTION

The yacc command 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.  This should only be used after the grammar and the associated actions are fully debugged. 

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 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. 

FILES

y.output
y.tab.c
y.tab.hdefines for token names
yacc.tmp,
yacc.debug, yacc.actstemporary files
/usr/lib/yaccparparser prototype for C programs

SEE ALSO

lex(1). 
Programmer’s Guide. 

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 is also reported. 

CAVEAT

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

September 02, 1992