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) {
allOf(Coll(
OUTPUTS(0).tokens(0)._1 == tokenId,
OUTPUTS(0).tokens(0)._2 >= tokenAmount,
OUTPUTS(0).propositionBytes == sellerPk.propBytes,
OUTPUTS(0).R4[Coll[Byte]].get == SELF.id)
)
} else { false } )
}
Sell contract is then as follows:
{
sigmaProp(allOf(Coll(
blake2b256(OUTPUTS(0).propositionBytes) == bbh,
OUTPUTS(0).value == buyBackAmount,
OUTPUTS(1).value >= toWithdraw,
OUTPUTS(1).propositionBytes == sellerPk.propBytes,
OUTPUTS(1).R4[Coll[Byte]].get == SELF.id
))
)
}
where bbh
is buyback script hash.
Playground version you can experiment with is available: https://scastie.scala-lang.org/oVlOW1GpTkWGLPLzDmJTxA .
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). Iām calling this smart orders. The big question, however, how to do front-end apps and UIs for smart order based DEXes.