PSM Contract

Zoe v0.24.0. Last updated August 25, 2022.

View the code on Github (Last updated: Aug 15, 2022)

The Parity Stability Module (PSM) contract allows users to convert Inter Stable Tokens (ISTs) to external stable tokens at a specified fixed ratio, and vice versa.

IST is an evolving, fully collateralized, cryptocurrency-backed decentralized stable token for the interchain ecosystem on the Agoric chain. IST is designed to maintain parity with the US dollar (USD) for broad accessibility and provides Agoric and the interchain ecosystem users an asset with minimum price volatility. In addition, IST is the native fee token for the Agoric platform and provides some of the core functionality and stability for the Agoric cryptoeconomy. Currently the PSM is the only minter of IST.

Which external stable tokens are supported is determined by governance in the form of a vote of the economic committee. Governance may elect to only support one external stable token, in which case only one PSM will be instantiated.

Instantiating the PSM

Each PSM instance pairs IST with one other token. To allow trading IST with multiple tokens, instantiate the PSM contract once for each.

Creating an Offer

The PSM contract supports 2 different offer types: swapping external stable tokens for IST tokens, and swapping IST tokens for external stable tokens. For both offer types only one user is required for a successful offer; in both cases the PSM itself acts as the other trading party.

Swapping External Stable Tokens for IST Tokens

To create an offer to swap external stable tokens for IST tokens, do the following:

1. Create an invitation using the makeWantMintedInvitation method.

   const myInvitation = E(publicFacet).makeWantMintedInvitation();

2. Create Amounts for the external stable tokens you want to trade and for the IST tokens you want to receive.

   ```js
   const giveAnchorAmount = AmountMath.make(anchorBrand, 200_000_000n);
   const wantMintedAmount = AmountMath.make(istBrand, 200_000_000n);
   ```
   

3. Create a proposal. Use the keywords In and Out, where In is the amount of external stable tokens you’re offering, and Out is the amount of IST tokens you expect to receive. Note that because the PSM will always be able to act as the other trading partner, this proposal doesn’t have (or need) an exit condition.

   ```js
   const myProposal = {
     give: { In: giveAnchorAmount },
     want: { Out: wantMintedAmount }
   };
   ```
   

4. Create a payment record containing the external stable tokens you’re trading to the PSM.

   const myPaymentRecord = { In: anchorPayment };

5. Create the offer, remembering to harden the proposal & payment record.

   const seat = E(zoe).offer(
     myInvitation,
     harden(myProposal),
     harden(myPaymentRecord)
   );

Swapping IST Tokens for External Stable Tokens

To create an offer to swap IST tokens for external stable tokens, do the following:

1. Create an invitation using the makeGiveMintedInvitation method.

   const myInvitation = E(publicFacet).makeGiveMintedInvitation();

2. Create Amounts for the IST tokens you want to trade and for the external stable tokens you want to receive. js const giveMintedAmount = AmountMath.make(istBrand, 200_000_000n); const wantAnchorAmount = AmountMath.make(anchorBrand, 200_000_000n);

3. Create and harden a proposal. Use the keywords In and Out, where In is the amount of IST tokens you’re offering, and Out is the amount of external stable tokens you expect to receive. Note that because the PSM will always be able to act as the other trading partner, this proposal doesn’t have (or need) an exit condition. js const myProposal = harden({ give: { In: giveMintedAmount }, want: { Out: wantAnchorAmount }, });

4. Create and harden a payment record containing the IST tokens you’re trading to the PSM.

   const myPaymentRecord = harden({ In: mintedPayment });

5. Create the offer.

   const seat = E(zoe).offer(myInvitation, myProposal, myPaymentRecord);