PacketSelector.hs

import Data.ByteString

type family mode :- a :: *

infixl 0 :-

data OnlyPacketB

type instance OnlyPacketB :- PacketB OnlyPacketB = PacketB OnlyPacketB
type instance OnlyPacketB :- PacketA OnlyPacketB = ByteString
type instance OnlyPacketB :- Int = Int
type instance OnlyPacketB :- Bool = Bool
type instance OnlyPacketB :- Float = Float
type instance OnlyPacketB :- Word = Word

data OnlyPacketA

type instance OnlyPacketA :- PacketB OnlyPacketA = ByteString
type instance OnlyPacketA :- PacketA OnlyPacketA = PacketA OnlyPacketA
type instance OnlyPacketA :- Int = Int
type instance OnlyPacketA :- Bool = Bool
type instance OnlyPacketA :- Float = Float
type instance OnlyPacketA :- Word = Word

data Packet s = Packet {
  packetA :: s :- PacketA s
, packetB :: s :- PacketB s
, packetC :: s :- Int
}

data PacketA s = PacketA {
  packetA1 :: s :- Bool
, packetA2 :: s :- Float
}

data PacketB s = PacketB {
  packetB1 :: s :- Word
, packetB2 :: s :- Word
}

example1 :: Packet OnlyPacketB
example1 = Packet mempty (PacketB 0 0) 10

example2 :: Packet OnlyPacketA
example2 = Packet (PacketA True 0) mempty 10