DEX orders with buyback guarantee, smart-order based DEXes

In this example we will consider a decentralized token-sale, where seller is providing buyback guarantees.

This guarantee is done in following way: a seller is requiring a buyer to create a buy order at some price and of some token amount also. Rest is going to the seller.

Every order can have unique buyback properties (to e.g. form a bonding curve).

We start with buyback contract. It has expiration (buyerPk && sigmaProp(HEIGHT > 100) condition), otherwise, the box has been spent if asked amount of tokens sent back to the original seller.

    val defined = OUTPUTS(0).R2[Coll[(Coll[Byte], Long)]].isDefined &&  OUTPUTS(0).R4[Coll[Byte]].isDefined
    (buyerPk && sigmaProp(HEIGHT > 100)) || sigmaProp (if (defined) {
          OUTPUTS(0).tokens(0)._1 == tokenId, 
          OUTPUTS(0).tokens(0)._2 >= tokenAmount,
          OUTPUTS(0).propositionBytes == sellerPk.propBytes,
          OUTPUTS(0).R4[Coll[Byte]].get ==
    } else { false } )

Sell contract is then as follows:

                blake2b256(OUTPUTS(0).propositionBytes) == bbh,
                OUTPUTS(0).value == buyBackAmount,
                OUTPUTS(1).value >= toWithdraw,
                OUTPUTS(1).propositionBytes == sellerPk.propBytes,
                OUTPUTS(1).R4[Coll[Byte]].get ==

where bbh is buyback script hash.

Playground version you can experiment with is available: .

Similarly to buy-back, we can enhance orders with different conditions, getting DEX functionality (and simple DEX orders) composable with complex logic (token-sale, liquidity providing etc). Iā€™m calling this smart orders. The big question, however, how to do front-end apps and UIs for smart order based DEXes.