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# EUTxO and English Auction

By
Travis Horn

# Auction Contract on the Playground

Lecture 1, Part 5

Lecture Video

# Start Plutus Playground Locally

Follow the instructions to run Plutus Playground locally.

Open your web browser to https://localhost:8009 to see the playground.

# Run the English Auction

Copy the contents of plutus-pioneer-program/code/week01/src/Week01/EnglishAuction.hs

Paste it into the editor of the playground in your browser

Remove the module header. You'll have to do this for every script you run in the playground. Delete lines 18-30 (should start with module and end with where).

Click Compile.

Once you see Compilation successful below the editor, the script is compiled.

Click Simulate.

By default there are two wallets. Both have 100,000,000 Lovelace (100 ADA) and 100,000,000 T. T is the token for the NFT.

Add another wallet by clicking Add Wallet.

There should be only 1 NFT, so make the T box under Wallet 1 say 1. Make the T box under both Wallet 2 and Wallet 3 say 0.

Have Wallet 1 start the auction by clicking start +.

Add a wait action by clicking Add Wait Action under Actions.

Have Wallet 2 make a bid by clicking bid +.

Add another wait action.

Have Wallet 3 make a bid.

Add another wait action.

Have Wallet 1 close the auction by clicking close +.

Finally, add another wait action.

With all of the actions added, we have to define the parameters.

Under Actions edit the Wallet 1: start action.

In the simulator, time is based on "slots" but time in Plutus is based on real time. So for spDeadline, we need to put the right value that corresponds to 10 slots.

See the guide on Converting Slots to POSIX Time

10 slots in Plutus Playground equates to 1596059101999 POSIX time. Enter that value in the spDeadline box.

Under spMinBid, enter 10000000 to make the minimum bid 10 ADA (10,000,000 Lovelace).

Under spCurrency, enter 66. This value is defined in the auction script (although there is some conversion that happens so you won't exactly see 66 anywhere in the code).

Under spToken, enter T.

Right next to this action, have the wait action that follows it Wait For... 1 slot.

For the Wallet 2: bid action...

Match the bpCurrency with the spCurrency when the auction was started by entering 66.

Match the bpToken with spToken by entering T.

Enter a bpBid of 10000000 (10 ADA)

Have the following wait action Wait For... 1 slot again.

For the Wallet 3: bid action, enter the same bpCurrency and bpToken, but have this action bid higher by entering 15000000.

Have the following wait action Wait Until... Slot 11 this time to make sure we pass the deadline.

For the Wallet 1: close action, match the bpCurrency and bpToken again.

Finally, make the last wait action Wait For... 1 slot so the transaction has time to be processed.

Click Evaluate to evaluate this simulation. You'll see the result after a few moments.

For each slot, you can see the transactions and the outputs.

During slot 0, the outputs look like this:

  • Wallet 1 gets 100 ADA and 1 T
  • Wallet 2 gets 100 ADA
  • Wallet 3 gets 100 ADA

Click on Slot 1 to view it.

During this slot, there is 1 input which is wallet 1. Everything from wallet 1 gets spent in this transaction.

The ouputs are:

  • Fee of 10 Lovelace (Only in the playground. Real world will be higher)
  • Wallet 1 gets ~97 ADA
  • Script gets 1 T and 2 ADA (In Cardano, every transaction must have some ADA in it.)

Keep following the slots to see how transactions behaved during the simulation.