Multiparty Agreement Combining Sign and Finalize Choices

I am researching the example around multi-party agreement

docs.daml.com

Multiple party agreement — DAML SDK 1.7.0 documentation

I was wondering if there is a way to combine the Sign and Finalize Choices below into 1 Choice.
The rational for this is that in this case no other logic would need to reside on when to call the “Sign Choice” versus the “Finalize Choice” in any connecting originating systems.

  choice Sign : ContractId Pending with
        signer : Party
      controller signer
        do
          -- Check the controller is in the toSign list, and if they are, sign the Pending contract
          assert (signer `elem` toSign)
          create this with alreadySigned = signer :: alreadySigned

 choice Finalize : ContractId Agreement with
        signer : Party
      controller signer
        do
          -- Check that all the required signatories have signed Pending
          assert (sort alreadySigned == sort finalContract.signatories)
          create finalContract

An alternative way would be to write a trigger, but wondered if there is maybe a way to accomplish this just inside DAML

Any thoughts ?

Hi there,

You can check each time in the Sign choice whether or not you’re finished. For example:

choice Sign: Either (ContractId Pending) (ContractId Agreement) 
    with 
      signer: Party 
    controller signer 
      do
        assert $ signer `elem` toSign
        let 
          newAlreadySigned = dedup $ signer :: alreadySigned
        if (sort newAlreadySigned) == (sort toSign) 
        then Right <$> create FinalContract with signatories = newAlreadySigned; ..
        else Left <$> create this with alreadySigned = newAlreadySigned

Also worth noting is that this approach, while possible, has a few negative side effects:

• Complicates the business logic by having 2 separate concerns in one choice, which also makes this code less flexible
• Complicates they frontend by having to handle one call that returns two different types

I would recommend keeping the choices separate and maybe having the frontend specially handle when they’re the last signer by automatically exercising the finalizing choice.