SYNOPSIS

    package Foo;
    use Module::Compile -base;

    sub pmc_compile {
        my ($class, $source) = @_;
        # Convert $source into (most likely Perl 5) $compiled_output
        return $compiled_output;
    }

In Bar.pm:

    package Bar;
    
    use Foo;
    ...
    no Foo

or (implied "no Foo;"):

    package Bar;
    
    {
        use Foo;
        ...
    }

To compile Bar.pm into Bar.pmc:

    perl -c Bar.pm

DESCRIPTION

This module provides a system for writing modules that compile other Perl modules.

Modules that use these compilation modules get compiled into some altered form the first time they are run. The result is cached into ".pmc" files.

Perl has native support for ".pmc" files. It always checks for them, before loading a ".pm" file.

EXAMPLE

You can declare a "v6.pm" compiler with:

    package v6;
    use Module::Compile -base;
    
    sub pmc_compile {
        my ($class, $source) = @_;
        # ... some way to invoke pugs and give p5 code back ...
    }

and use it like:

    # MyModule.pm
    use v6-pugs;
    module MyModule;
    # ...some p6 code here...
    no v6;
    # ...back to p5 land...

On the first time this module is loaded, it will compile Perl 6 blocks into Perl 5 (as soon as the "no v6" line is seen), and merge it with the Perl 5 blocks, saving the result into a MyModule.pmc file.

The next time around, Perl 5 will automatically load MyModule.pmc when someone says "use MyModule". On the other hand, Perl 6 can run MyModule.pm s a Perl 6 module just fine, as "use v6-pugs" and "no v6" both works in a Perl 6 setting.

The v6.pm module will also check if MyModule.pmc is up to date. If it is, then it will touch its timestamp so the ".pmc" is loaded on the next time.

BENEFITS

Module::Compile compilers gives you the following benefits:

Ability to mix many source filterish modules in a much more sane manner. Module::Compile controls the compilation process, calling each compiler at the right time with the right data.
Ability to ship precompiled modules without shipping Module::Compile and the compiler modules themselves.
Easier debugging of compiled/filtered code. The ".pmc" has the real code you want to see.
Zero additional runtime penalty after compilation, because "perl" has already been doing the ".pmc" check on every module load since 1999!

PARSING AND DISPATCH

NOTE: *** NOT FULLY IMPLEMENTED YET ***

Module::Compile attempts to make source filtering a sane process, by parsing up your module's source code into various blocks; so that by the time a compiler is called it only gets the source code that it should be looking at.

This section describes the rather complex algorithm that Module::Compile uses.

First, the source module is preprocessed to hide heredocs, since the content inside heredocs can possibly confuse further parsing.

Next, the source module is divided into a shallow tree of blocks:

    PREAMBLE:
        (SUBROUTINE | BAREBLOCK | POD | PLAIN)S
    PACKAGES:
        PREFACE
        (SUBROUTINE | BAREBLOCK | POD | PLAIN)S
    DATA

All of these blocks begin and end on line boundaries. They are described as follows:

    PREAMBLE - Lines before the first C<package> statement.
    PACKAGES - Lines beginning with a C<package statement and continuing
        until the next C<package> or C<DATA> section.
    DATA - The DATA section. Begins with the line C<__DATA__> or
        C<__END__>.
    SUBROUTINE - A top level (not nested) subroutine. Ending '}' must be
        on its own line in the first column.
    BAREBLOCK - A top level (not nested) code block. Ending '}' must be
        on its own line in the first column.
    POD - Pod sections beginning with C<^=\w+> and ending with C<=cut>.
    PLAIN - Lines not in SUBROUTINE, BAREBLOCK or POD.
    PREFACE - Lines before the first block in a package.

Next, all the blocks are scanned for lines like:

    use Foo qw'x y z';
    no Foo;

Where Foo is a Module::Compile subclass.

The lines within a given block between a "use" and "no" statement are marked to be passed to that compiler. The end of an inner block effectively acts as a "no" statement for any compile sections in that block. "use" statements in a PREFACE apply to all the code in a PACKAGE. "use" statements in a PREAMBLE apply to all the code in all PACKAGES.

After all the code has been parsed into blocks and the blocks have been marked for various compilers, Module::Compile dispatches the code blocks to the compilers. It does so in a most specific to most general order. So inner blocks get compiled first, then outer blocks.

A compiler may choose to declare that its result not be recompiled by some other containing parser. In this case the result of the compilation is replaced by a single line containing the hexadecimal digest of the result in double quotes followed by a semicolon. Like:

    "f1d2d2f924e986ac86fdf7b36c94bcdf32beec15";

The rationale of this is that randoms strings are usally left alone by compilers. After all the compilers have finished, the digest lines will be expanded again.

Every bit of the default process described above is overridable by various methods.

DISTRIBUTION SUPPORT

Module::Install makes it terribly easy to prepare a module distribution with compiled .pmc files. Module::Compile installs a Module::Install::PMC plugin. All you need to do is add this line to your Makefile.PL:

    pmc_support;