O - Generic interface to Perl Compiler backends
perl -MO=Backend[,OPTIONS] foo.pl
This is the module that is used as a frontend to the Perl Compiler.
Most compiler backends use the following conventions:
OPTIONS consists of a comma-separated list of words
(no white-space). The -v option usually puts the backend into verbose mode. The -ofile option generates output to file instead of stdout. The -D option followed by various letters turns on various internal debugging
flags. See the documentation for the desired backend (named B::Backend for the example above) to find out about that backend.
This section is only necessary for those who want to write a compiler backend module that can be used via this module.
The command-line mentioned in the SYNOPSIS section corresponds to the Perl code
use O ("Backend", OPTIONS);
The import function which that calls loads in the appropriate
B::Backend module and calls the compile function in that package, 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
-c) and an
END 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
-c 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.
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 compile. When the user types
perl -MO=Foo,OPTIONS foo.pl
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 B module's functionality.
Malcolm Beattie, mbeattie@sable.ox.ac.uk
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