perl -c -MModule::Inline::C=PACKAGE blib/lib/Foo/Bar.pm # (or similar)

##</code><code>##

package Foo::Bar;
use 5.006;
use strict;
use warnings;

our $VERSION = '0.01';

use Module::Inline::C <<'HERE';
int
fac (int x)
{
    if (x <= 0) return(1);
    return(x*fac(x-1));
}
HERE

# ordinary perl code and more inlined C here

# This is for triggering the XS generation if applicable:
use Module::Inline::C 'END';

1;

__END__

=head1 NAME

Foo::Bar - Perl extension for blah blah blah

=cut

##</code><code>##

package Module::Inline::C;
use strict;
use warnings;

# Should work for *one Inline::C-using package per distribution only*
# right now!

our @INLINE_ARGS;
our $PACKAGE = 0;

sub import {
    my $class = shift;
    my @args = @_;

    if (@args==1 and $args[0] eq 'PACKAGE') {
        warn 'Setting PACKAGE option';
        # trigger packaging/XS generation mode
        $PACKAGE = 1;
        return 1;
    }
    elsif (@args == 1 and $args[0] eq 'END') {
        # All C code was received. Generate XS.
        return unless $PACKAGE;
        _generate();
    }
    elsif ($PACKAGE == 1) {
        warn 'Saving arguments to Inline because we\'re in PACKAGE mode';
        # Write out C code
        my ($pkg) = caller(0);
        push @INLINE_ARGS, {pkg => $pkg, args => \@args};
    }
    else {
        # try to load dll/so first (user mode)
        warn 'Trying to load shared obj file';
        my ($pkg) = caller(0);
        require XSLoader;
        eval {
            XSLoader::load($pkg);
        };
        return 1 if not $@;
        # Compile using Inline::C (author mode)
        warn 'failed to load shared obj file, resorting to inline';
        eval "package $pkg; require Inline; Inline->import('C', \@args);";
        die $@ if $@;
        return 1;
    }
}

sub _generate {
    require File::Spec;
    require Inline::C2XS;
    mkdir('src');
    foreach my $call (@INLINE_ARGS) {
        my $pkg = $call->{pkg};
        if (@{$call->{args}} != 1) {
            require Data::Dumper;
            warn "Skipping Inline C call from package $pkg with arguments: ".Dumper($call->{args});
            next;
        }
        my $file = $pkg;
        $file =~ s/^(?:[^:]*::)*([^:]+)$/$1/;
        $file .= '.c';
        open my $fh, '>>', File::Spec->catfile('src', $file) or die $!;
        print $fh "\n".$call->{args}[0];
        close $fh;
        Inline::C2XS::c2xs($pkg, $pkg);
    }
}
1;