package Before;
use Acme::Damn;

use overload
    '&{}' => sub {
        my $f = shift();
        my $ref = damn($f);
        return sub {
            print "Stuff before\n";
            my @rv = $ref->(@_);
            bless($ref, __PACKAGE__);
            return @rv;
        };
    };
1;

##</code><code>##

$ perl -MBefore -e 'my $foo = bless(sub { print shift()."\n" } => 'Before'); $foo->("foo"); $foo->("bar")'
Stuff before
foo
Stuff before
bar