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<title>yacc(1) - Plan 9 from User Space</title>
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<tr><td width=20><td><b>YACC(1)</b><td align=right><b>YACC(1)</b>
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<br>
<p><font size=+1><b>NAME </b></font><br>
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yacc – yet another compiler-compiler<br>
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<p><font size=+1><b>SYNOPSIS </b></font><br>
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<tt><font size=+1>yacc</font></tt> [ <i>option ...</i> ] <i>grammar<br>
</i>
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<p><font size=+1><b>DESCRIPTION </b></font><br>
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<i>Yacc</i> converts a context-free grammar and translation code into
a set of tables for an LR(1) parser and translator. The grammar
may be ambiguous; specified precedence rules are used to break
ambiguities.
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The output file, <tt><font size=+1>y.tab.c</font></tt>, must be compiled by the C compiler to
produce a program <tt><font size=+1>yyparse</font></tt>. This program must be loaded with a
lexical analyzer function, <tt><font size=+1>yylex(void)</font></tt> (often generated by <a href="../man1/lex.html"><i>lex</i>(1)</a>),
with a <tt><font size=+1>main(int argc, char *argv[])</font></tt> program, and with an error
handling routine,
<tt><font size=+1>yyerror(char*)</font></tt>.
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The options are<br>
<tt><font size=+1>−o</font></tt> <i>output</i> Direct output to the specified file instead of <tt><font size=+1>y.tab.c</font></tt>.<br>
<tt><font size=+1>−D</font></tt><i>n</i> Create file <tt><font size=+1>y.debug</font></tt>, containing diagnostic messages. To incorporate
them in the parser, compile it with preprocessor symbol <tt><font size=+1>yydebug</font></tt>
defined. The amount of diagnostic output from the parser is regulated
by value <i>n</i>. The value 0 reports errors; 1 reports reductions;
higher values (up to 4) include
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more information about state transitions.<br>
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<tt><font size=+1>−v</font></tt> Create file <tt><font size=+1>y.output</font></tt>, containing a description of the parsing
tables and of conflicts arising from ambiguities in the grammar.<br>
<tt><font size=+1>−d</font></tt> Create file <tt><font size=+1>y.tab.h</font></tt>, containing <tt><font size=+1>#define</font></tt> statements that associate
<i>yacc</i>-assigned ‘token codes’ with user-declared ‘token names’.
Include it in source files other than <tt><font size=+1>y.tab.c</font></tt> to give access to
the token codes.<br>
<tt><font size=+1>−s</font></tt> <i>stem</i> Change the prefix <tt><font size=+1>y</font></tt> of the file names <tt><font size=+1>y.tab.c</font></tt>, <tt><font size=+1>y.tab.h</font></tt>,
<tt><font size=+1>y.debug</font></tt>, and <tt><font size=+1>y.output</font></tt> to <i>stem</i>.<br>
<tt><font size=+1>−S</font></tt> Write a parser that uses Stdio instead of the <tt><font size=+1>print</font></tt> routines
in libc.
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The specification of <i>yacc</i> itself is essentially the same as the
UNIX version described in the references mentioned below. Besides
the <tt><font size=+1>−D</font></tt> option, the main relevant differences are:<br>
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The interface to the C environment is by default through <tt><font size=+1><libc.h></font></tt>
rather than <tt><font size=+1><stdio.h></font></tt>; the <tt><font size=+1>−S</font></tt> option reverses this.<br>
The parser accepts UTF input text (see <a href="../man7/utf.html"><i>utf</i>(7)</a>), which has a couple
of effects. First, the return value of <tt><font size=+1>yylex()</font></tt> no longer fits
in a <tt><font size=+1>short</font></tt>; second, the starting value for non-terminals is now
0xE000 rather than 257.<br>
The generated parser can be recursive: actions can call <i>yyparse</i>,
for example to implement a sort of <tt><font size=+1>#include</font></tt> statement in an interpreter.<br>
Finally, some undocumented inner workings of the parser have been
changed, which may affect programs that know too much about its
structure.<br>
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<p><font size=+1><b>FILES </b></font><br>
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<tt><font size=+1>y.output<br>
y.tab.c<br>
y.tab.h<br>
y.debug<br>
y.tmp.*</font></tt> temporary file<br>
<tt><font size=+1>y.acts.*</font></tt> temporary file<br>
<tt><font size=+1>/usr/local/plan9/lib/yaccpar<br>
</font></tt>
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parser prototype<br>
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<tt><font size=+1>/usr/local/plan9/lib/yaccpars<br>
</font></tt>
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parser prototype using stdio<br>
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<p><font size=+1><b>SOURCE </b></font><br>
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<tt><font size=+1>/usr/local/plan9/src/cmd/yacc.c<br>
</font></tt>
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<p><font size=+1><b>SEE ALSO </b></font><br>
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<a href="../man1/lex.html"><i>lex</i>(1)</a><br>
S. C. Johnson and R. Sethi, “Yacc: A parser generator”, <i>Unix Research
System Programmer’s Manual,</i> Tenth Edition, Volume 2<br>
B. W. Kernighan and Rob Pike, <i>The UNIX Programming Environment,</i>
Prentice Hall, 1984<br>
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<p><font size=+1><b>BUGS </b></font><br>
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The parser may not have full information when it writes to <tt><font size=+1>y.debug</font></tt>
so that the names of the tokens returned by <tt><font size=+1>yylex</font></tt> may be missing.<br>
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