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            <h1>O</h1>


  <!--    -->
<ul><li><a href="#NAME">NAME</a><li><a href="#SYNOPSIS">SYNOPSIS</a><li><a href="#DESCRIPTION">DESCRIPTION</a><li><a href="#CONVENTIONS">CONVENTIONS</a><li><a href="#IMPLEMENTATION">IMPLEMENTATION</a><li><a href="#BUGS">BUGS</a><li><a href="#AUTHOR">AUTHOR</a></ul><a name="NAME"></a><h1>NAME</h1>
<p>O - Generic interface to Perl Compiler backends</p>
<a name="SYNOPSIS"></a><h1>SYNOPSIS</h1>
<pre class="verbatim"><ol><li>	perl -MO=[-q,]Backend[,OPTIONS] foo.pl</li></ol></pre><a name="DESCRIPTION"></a><h1>DESCRIPTION</h1>
<p>This is the module that is used as a frontend to the Perl Compiler.</p>
<p>If you pass the <code class="inline">-q</code> option to the module, then the STDOUT
filehandle will be redirected into the variable <code class="inline"><span class="i">$O::BEGIN_output</span></code>

during compilation.  This has the effect that any output printed
to STDOUT by BEGIN blocks or use'd modules will be stored in this
variable rather than printed. It's useful with those backends which
produce output themselves (<code class="inline"><span class="w">Deparse</span></code>
, <code class="inline"><span class="w">Concise</span></code>
 etc), so that
their output is not confused with that generated by the code
being compiled.</p>
<p>The <code class="inline">-qq</code> option behaves like <code class="inline">-q</code>, except that it also closes
STDERR after deparsing has finished. This suppresses the "Syntax OK"
message normally produced by perl.</p>
<a name="CONVENTIONS"></a><h1>CONVENTIONS</h1>
<p>Most compiler backends use the following conventions: OPTIONS
consists of a comma-separated list of words (no white-space).
The <code class="inline">-<span class="w">v</span></code>
 option usually puts the backend into verbose mode.
The <code class="inline">-<span class="w">ofile</span></code>
 option generates output to <b>file</b> instead of
stdout. The <code class="inline">-<span class="w">D</span></code>
 option followed by various letters turns on
various internal debugging flags. See the documentation for the
desired backend (named <code class="inline"><span class="w">B::Backend</span></code>
 for the example above) to
find out about that backend.</p>
<a name="IMPLEMENTATION"></a><h1>IMPLEMENTATION</h1>
<p>This section is only necessary for those who want to write a
compiler backend module that can be used via this module.</p>
<p>The command-line mentioned in the SYNOPSIS section corresponds to
the Perl code</p>
<pre class="verbatim"><ol><li>    <a class="l_k" href="functions/use.html">use</a> <span class="w">O</span> <span class="s">(</span><span class="q">&quot;Backend&quot;</span><span class="cm">,</span> <span class="w">OPTIONS</span><span class="s">)</span><span class="sc">;</span></li></ol></pre><p>The <code class="inline"><span class="w">O::import</span></code>
 function loads the appropriate <code class="inline"><span class="w">B::Backend</span></code>
 module
and calls its <code class="inline"><span class="w">compile</span></code>
 function, passing it OPTIONS. That function
is expected to return a sub reference which we'll call CALLBACK. Next,
the "compile-only" flag is switched on (equivalent to the command-line
option <code class="inline">-c</code>
) and a CHECK block is registered which calls
CALLBACK. Thus the main Perl program mentioned on the command-line is
read in, parsed and compiled into internal syntax tree form. Since the
<code class="inline">-c</code>
 flag is set, the program does not start running (excepting BEGIN
blocks of course) but the CALLBACK function registered by the compiler
backend is called.</p>
<p>In summary, a compiler backend module should be called "B::Foo"
for some foo and live in the appropriate directory for that name.
It should define a function called <code class="inline"><span class="w">compile</span></code>
. When the user types</p>
<pre class="verbatim"><ol><li>    <span class="w">perl</span> -<span class="w">MO</span>=<span class="w">Foo</span><span class="cm">,</span><span class="w">OPTIONS</span> <span class="w">foo</span>.<span class="w">pl</span></li></ol></pre><p>that function is called and is passed those OPTIONS (split on
commas). It should return a sub ref to the main compilation function.
After the user's program is loaded and parsed, that returned sub ref
is invoked which can then go ahead and do the compilation, usually by
making use of the <code class="inline"><span class="w">B</span></code>
 module's functionality.</p>
<a name="BUGS"></a><h1>BUGS</h1>
<p>The <code class="inline">-q</code> and <code class="inline">-qq</code> options don't work correctly if perl isn't
compiled with PerlIO support : STDOUT will be closed instead of being
redirected to <code class="inline"><span class="i">$O::BEGIN_output</span></code>
.</p>
<a name="AUTHOR"></a><h1>AUTHOR</h1>
<p>Malcolm Beattie, <code class="inline"><span class="w">mbeattie</span><span class="i">@sable</span>.<span class="w">ox</span>.<span class="w">ac</span>.<span class="w">uk</span></code>
</p>




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