spiders.bson

* build a spider
* build a megaspider
* build a registry of megaspider

$s = Spider->new({
  bson_type => BSON_INT32,
  perl_type => [ typetype => 'name1' ],

  from_perl => [
    [ typetype => name1 => sub { ... } ],
    [ typetype => name2 => sub { ... } ],
    [ typetype => name3 => sub { ... } ],
    [ typetype => name4 => sub { ... } ],

    # from DateTime -> BSON array [ y, m, d ]
    [ class => DateTime => sub {
      my ($v, $ctx) = @_;

      # Option 1: Trust the registry to get the right type:
      $ctx->registry->to_bson([ $v->year, $v->month, $v->day ]);

      # Option 2: We know better.
      $r->bson_array([
        $r->to_typed_bson('int32', $v->year),
        $r->to_typed_bson('int32', $v->month),
        $r->to_typed_bson('int64', $v->day),
      ]);

      # Option 3: We have many registries:
      $other_registry->to_bson([ ... ]);
    } ],

    # Concrete examples:
    [ core  => number     => sub { $_ } ],
    [ class => 'DateType' => sub { $_->epoch } ],
    [ private => name => sub { $_->epoch } ],
  ],
  to_perl   => sub { ... }, # or some inlineable thingy someday
});

$m = MegaSpider->new({
  spiders   => \@spiders,
});

$r = SpiderWeb->new({
  private_types => {
    name => sub { ... },
  },
  megaspiders => [
    [ Foo => $m0 ],
    [ Bar => $m1 ],
    [ Baz => $m2 ],
  ],
});

$r->to_bson($perl_value)

$muxer = SpiderWeb::Muxer->new({
  private_types => {
    name => sub { ... },
  },
  registries => \@webs,
});

sub SpiderWeb::to_bson {
  my ($self, $perl_value) = @_;

  for my $spider ($self->spiders->@*) {
    my $res = $spider->to_bson($perl_value, $self);
    next if is_NO($res);
    return $res;
  }

  return NO;
}

sub SpiderWeb::Muxer::to_bson {
  my ($self, $perl_value) = @_;

  for my $web ($self->registries->@*) {
    my $res = $web->to_bson($perl_value);
    next if is_NO($res);
    return $res;
  }

  return NO;
}

sub Spider::to_bson {
  my ($self, $perl_value, $r) = @_;

  for my $cond ($self->from_perl->@*) {
    my ($typetype, $typename, $code) = @$cond;
    my $check = $self->resolve_type($typetype, $typename);
    next unless $check->($perl_value);
    return $code->($perl_value);
  }

  return NO;
}