# Pastebin mZUJJRXd
import options

type
  Tx = ref object
    prevTx: Option[Tx] # either contains a tx; or we don't know about it

let genesisTx* = Tx(prevTx: none(Tx))
genesisTx.prevTx = some(genesisTx);

proc `$`(tx: Tx): string {.noSideEffect.} =
  if (tx.prevTx == some(genesisTx)):
    return "Tx([genesis])"
  "Tx(prevTx: " & $tx.prevTx & ", sig: )"

echo $genesisTx