yacc -- Command

Parser generator
yacc [option ...] file
cc y.tab.c [-ly]

Many  programs process  highly structured input  according to  given rules.
Compilers are  a familiar  example.  Two of  the most complicated  parts of
such  programs are  lexical analysis and  parsing (sometimes  called syntax
analysis). The  COHERENT system includes two powerful  tools called lex and
yacc to assist  you in performing these tasks.  lex  takes a set of lexical
rules and  writes a lexical analyzer,  whereas yacc takes a  set of parsing
rules and writes  a parser; both output C source  code that can be compiled
into a full program.

The  term yacc  is an  acronym for  ``yet another  compiler-compiler''.  In
brief, the  yacc input file describes  a context free grammar  using a BNF-
like syntax.  The output is a file y.tab.c; it contains the definition of a
C  function yyparse(),  which parses  the language  described in  file. The
output is  ready for processing  by the C  compiler cc. Ambiguities  in the
grammar are reported to  the user, but resolved automatically by precedence
rules.   The user  must provide  a lexical scanner  yylex(), which  you may
generate with  lex. The yacc library includes  default definitions of main,
yylex,  and yyerror,  and may  be included  with the option  -ly on  the cc
command line.

yacc recognizes the following options:

-d   Enable debugging output; implies -v.

-hdr headerfile
     Put the header output in headerfile instead of y.tab.h.

-items N
     Allow N items  per state.  This option is designed  to help yacc users
     deal with the ANSI C grammar.

-l listfile
     Place a description of the state machine, tokens, parsing actions, and
     statistics in file listfile.

-sprod N
     Allow N symbols per  production; default, 20.  This option is designed
     to help yacc users deal with the ANSI C grammar.

-st  Print statistics on the standard output.

-v   Verbose option.   Like -l, but places the listing  in file y.output by
     default.

The following options are useful if table overflow messages appear:

-nterms N
     Allow for N nonterminals; default, 100.

-prods N
     Allow for N productions (rules); default, 350.

-states N
     Allow for N states; default, 300.

-terms N
     Allow for N terminal symbols; default 100.

-types N
     Allow for N types; default, ten.

Files

y.tab.c -- C source output
y.tab.h -- Default C header output
y.output -- Default listing output
/lib/yyparse.c -- Protoparser
/tmp/y[ao]* -- Temporaries
/usr/lib/liby.a -- Library

See Also

cc,
commands,
lex,
Programming COHERENT
Introduction to yacc, Yet Another Compiler-Compiler

Diagnostics

yacc writes  onto the standard error the number  of R/R (reduce/reduce) and
S/R (shift/reduce) conflicts (ambiguities).

Notes

The version of  yacc shipped prior to release 4.2  of COHERENT included the
header file <action.h> in its output.  This file's data are now built
into parser skeleton in /lib/yyparse, thus obviating <action.h>. This
header has  been dropped from  COHERENT.  You should re-run  yacc to update
the source files generated by previous versions of yacc.

© 2012 by Stephen A. Ness