O(3)

NAME
O - Generic interface to Perl Compiler backends

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

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

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 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.

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