Note that $self in the callback doesn't make much sense
Well - yes and no. Without the $self certainly works as you have it, but it is much easier to use $self. $self in this case is simply the topic of discussion - the guy who called the method - even if he isn't the one who owns the method. Using the callback as a method also allows the following to work without the predeclared "my $fp".
my $fp = Foo::Parse->new('Fooparser', \&Some::Other::Class::Method);
You can call the Some::Other::Class::Method with any object that "does" everything that Method requires. This will be easier to validate for in Perl 6 as even the anonymous method can have a signature that can make sure that whatever gets passed to it has the appropriate capabilities.
my @a=qw(random brilliant braindead); print $a[rand(@a)];