Repay.md

Repay Exercise

In this exercise, you'll learn how to repay DAI debt by interacting with Vat and DaiJoin contracts directly.

The starter code for this exercise is provided in foundry/src/exercises/Repay.sol

Solution is in foundry/src/solutions/Repay.sol

Hint: notes/code/DssProxyActions.sol

Task 1 - Repay partial debt

function repay(uint256 amt) external auth {
    // Write your code here
}

• Transfer DAI from the caller, approve, and join it into the Vat via DaiJoin.
• Calculate the debt to repay using Math.calcDebtToRepay.
• Call vat.frob to wipe debt (zero dink, negative dart).
• Refund any excess DAI remaining in the Vat back to the caller.

Task 2 - Repay all debt

function repayAll() external auth {
    // Write your code here
}

• Calculate the exact DAI amount needed using Math.calcDaiToRepayAll.
• Transfer DAI from the caller, approve, and join it into the Vat via DaiJoin.
• Get the urn's art (total debt units) and call vat.frob with negative dart equal to -art.

Test

forge test --fork-url $FORK_URL --match-path test/Repay.t.sol -vvv