MirOS Manual: O(3p)


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

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 them-
     selves ("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 "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 CALL-
     BACK. 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

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

     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 compila-
     tion 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"

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