NAME

       O - Generic interface to Perl Compiler backends

SYNOPSIS

               perl -MO=[-q,]Backend[,OPTIONS] foo.pl

DESCRIPTION

       This is the module that is used as a frontend to the Perl Compiler.

       If you pass the "-q" option to the module, then the STDOUT filehandle will be redirected into the
       variable $O::BEGIN_output 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 ("Deparse", "Concise" etc), so that their output is not confused
       with that generated by the code being compiled.

       The "-qq" option behaves like "-q", except that it also closes STDERR after deparsing has finished. This
       suppresses the "Syntax OK" message normally produced by perl.

CONVENTIONS

       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.

IMPLEMENTATION

       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 "O::import" function loads the appropriate "B::Backend" module and calls its "compile" 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 "-c") 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 "-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.

BUGS

       The "-q" and "-qq" options don't work correctly if perl isn't compiled with PerlIO support : STDOUT will
       be closed instead of being redirected to $O::BEGIN_output.

AUTHOR

       Malcolm Beattie, "mbeattie@sable.ox.ac.uk"