ghci.txt

ghci -fobject-code StgTicket.cmm Ticket.hs
GHCi, version 9.4.4: https://www.haskell.org/ghc/  :? for help
[1 of 1] Compiling Ticket           ( Ticket.hs, Ticket.o ) [Source file changed]
Ok, one module loaded.
ghci> import Data.IORef
ghci> import System.Mem
ghci> ref <- newIORef =<< mkTicket
ghci> flip addFinalizer (putStrLn "YOLO") =<< readIORef ref
ghci> performGC
ghci> writeIORef ref undefined
ghci> performGC
YOLO
ghci> 

StgTicket.cmm

#include "Cmm.h"

INFO_TABLE(stg_TICKET, 0, 0, PRIM, "TICKET", "TICKET")
  ()
{
  return ();
}

stg_newTicketzh ()
{
  P_ ticket;

  ALLOC_PRIM_ (SIZEOF_StgHeader, stg_newTicketzh);

  ticket = Hp - SIZEOF_StgHeader + WDS(1);
  SET_HDR(ticket,stg_TICKET_info,CCCS);

  return (ticket);
}

Ticket.hs

{-# LANGUAGE GHCForeignImportPrim #-}
{-# LANGUAGE MagicHash #-}
{-# LANGUAGE UnboxedTuples #-}
{-# LANGUAGE UnliftedFFITypes #-}

module Ticket
  ( Ticket,
    mkTicket,
    addFinalizer,
  )
where

import GHC.Exts
import GHC.Types

newtype Ticket = MkTicket Any

mkTicket :: IO Ticket
mkTicket = IO $ \s0 -> case stg_newTicket# s0 of
  (# s1, t #) -> (# s1, MkTicket t #)

addFinalizer :: Ticket -> IO () -> IO ()
addFinalizer t (IO fin) = IO $ \s0 -> case mkWeak# t t fin s0 of
  (# s1, _ #) -> (# s1, () #)

foreign import prim "stg_newTicketzh" stg_newTicket# :: State# s -> (# State# s, Any #)