O(3)                   Perl Programmers Reference Guide                   O(3)

       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

3rd Berkeley Distribution    perl 5.005, patch 02                         O(3)