DAML

module Iou where

template Iou
  with
    issuer : Party
    owner : Party
    currency : Text
    amount : Decimal
  where
    signatory issuer
    observer owner

    choice Transfer : ContractId Iou
      with
        newOwner : Party
      controller owner
      do create this with owner = newOwner

    choice Split : (ContractId Iou, ContractId Iou)
      with
        splitAmount : Decimal
      controller owner
      do
        let rest = amount - splitAmount
        assert (splitAmount > 0.0)
        assert (rest > 0.0)
        iouSplit <- create this with amount = splitAmount
        iouRest <- create this with amount = rest
        return (iouSplit, iouRest)

    choice Merge : ContractId Iou
      with
        otherCid : ContractId Iou
      controller owner
      do
        otherIou <- fetch otherCid
        assert (issuer == otherIou.issuer)
        assert (currency == otherIou.currency)
        archive otherCid
        create this with amount = amount + otherIou.amount