Module 0 · Exercise 1 · ~20 min

Daml Playground

Work through a set of scenarios on a richer simulated Daml ledger. Each scenario gives you a goal ledger state — use the available actions to reach it. The simulator auto-checks when you get there.

Templates in play:

template Iou
  with issuer: Party, owner: Party, amount: Decimal, currency: Text
  where
    signatory issuer, owner
    choice Transfer : ContractId Iou with newOwner: Party  controller owner
    choice Split    : (ContractId Iou, ContractId Iou) with splitAmount: Decimal controller owner
    choice Archive_ : ()                         controller issuer

template TransferProposal
  with iouCid: ContractId Iou, proposedOwner: Party, currentOwner: Party
  where
    signatory currentOwner
    observer  proposedOwner
    choice Accept : ContractId Iou  controller proposedOwner

Mint and transfer

Goal: There is an active Iou contract owned by Bob with amount 100 USD, issued by Alice. That's it — one active contract, one archived, Bob as current owner.

Ledger

Actions

Split and send

Goal: Alice starts with a 100 USD Iou owned by Bob. Bob splits it into 60 + 40 and transfers the 60 to Carol. End state: Bob holds 40 USD (active); Carol holds 60 USD (active); original 100 USD is archived.

Ledger

Actions

Propose / accept pattern

Goal: Transfer ownership from Bob to Carol using the propose/accept pattern: Bob creates a TransferProposal for his Iou to Carol, Carol accepts it, resulting in a new Iou owned by Carol (the original archived). This pattern is important because in real Daml, both signatories must authorize, so the owner can't unilaterally transfer to a party who hasn't consented.

Ledger

Actions

Reflection

Before marking this exercise complete, answer these to yourself:

What's the difference between Transfer (which acts unilaterally) and Accept (which requires two steps)?
When Bob splits a 100 USD Iou into 60 + 40, how many contracts exist after the operation, and which one is archived?
Why does the synchronizer need to order propose/accept but not need to see the amounts?

(Click each line to mark it read. Purely for your own tracking.)