> ## Documentation Index
> Fetch the complete documentation index at: https://docs.monolith.market/llms.txt
> Use this file to discover all available pages before exploring further.

# Lender

> Core lending pool contract for the Monolith protocol

# Lender Contract

The Lender contract implements the core lending functionality for an instance: collateral management, debt accounting, interest accrual, liquidations, redemptions, and PSM conversions.

[Contract implementation](https://github.com/MonolithMarket/Monolith/blob/main/src/Lender.sol)

## User-Facing Functions

### adjust

```solidity theme={null}
function adjust(address account, int collateralDelta, int debtDelta, bool chooseRedeemable) external
```

Adjusts a user's position by modifying collateral and/or debt. This is the primary function for depositing, withdrawing, borrowing, repaying and changing redemption status.

**Parameters:**

* `account`: Address of the position to adjust
* `collateralDelta`: Amount to add (positive) or remove (negative) collateral (in wei)
* `debtDelta`: Amount to borrow (positive) or repay (negative) debt (in wei)
* `chooseRedeemable`: True to turn on redeemable (free debt) mode. False to turn off.

**Requirements:**

* If `collateralDelta > 0`: `msg.sender` must provide collateral in (approval required)
* If `debtDelta > 0`: Position must remain solvent after the change
* If `debtDelta < 0`: Caller must provide Coin to repay (approval required)
* If decreasing collateral or increasing debt: caller must be `account` or a delegated address
* If `debtDelta != 0`: resulting debt must be 0 or ≥ `minDebt`

**Behavior:**

* Automatically accrues interest before adjustment
* Updates collateral and debt of the borrower
* Maintains minimum debt requirements
* Emits position update events

***

### liquidate

```solidity theme={null}
function liquidate(address borrower, uint repayAmount, uint minCollateralOut) external returns (uint collateralOut)
```

Liquidates an undercollateralized position to maintain protocol solvency. Oracle‑gated; disabled when price is stale/invalid.

**Parameters:**

* `borrower`: Address of the position to liquidate
* `repayAmount`: Amount of debt to repay (in wei)
* `minCollateralOut`: Minimum collateral amount to receive (caller protection)

**Returns:**

* `collateralOut`: Amount of collateral received by liquidator

**Requirements:**

* Borrower loan must be unhealthy at the oracle price and liquidations allowed
* Up to 25% of total debt can be liquidated per call (minimum 10,000 Coin chunk, or full debt if smaller)
* Liquidator must provide Coin to repay and set an acceptable `minCollateralOut`

**Liquidation Process:**

1. Accrue interest on borrower's position
2. Verify liquidation conditions
3. Transfer Coin from liquidator to repay debt
4. Calculate collateral reward with incentive
5. Transfer collateral to liquidator
6. Update borrower's position

**Incentive Calculation:**

* Incentive scales from 0% (at collateralFactor) up to 10% (5 percentage points above collateralFactor), linearly in between

***

### redeem

```solidity theme={null}
function redeem(uint amountIn, uint minAmountOut) external returns (uint amountOut)
```

Redeems Coin for collateral from the redeemable pool at the oracle price minus a redemption fee.

**Parameters:**

* `amountIn`: Amount of Coin to redeem (in wei)
* `minAmountOut`: Minimum collateral amount to receive (slippage protection)

**Returns:**

* `amountOut`: Amount of collateral received

**Requirements:**

* Redemptions must be allowed (fresh oracle)
* Redeemable borrowers must have sufficient collateral to redeem and debt to repay
* `amountOut` must be ≥ `minAmountOut`

**Redemption Amount:**

* `amountOut = amountIn * 1e18 * (10000 - redeemFeeBps) / price / 10000`

***

### sell

```solidity theme={null}
function sell(uint coinIn, uint minAssetOut) external returns (uint assetOut)
```

Sells Coin for PSM asset at a 1:1 nominal rate (decimals‑adjusted). No fee.

**Parameters:**

* `coinIn`: Amount of Coin to sell (in wei)
* `minAssetOut`: Minimum PSM asset amount to receive

**Returns:**

* `assetOut`: Amount of PSM asset received

**Requirements:**

* PSM must be configured with a `psmAsset`
* Sufficient PSM reserves available
* `assetOut` must be ≥ `minAssetOut`

**Pricing:**

* Decimals conversion between 18‑dec Coin and `psmAsset` decimals. No fee.

***

### buy

```solidity theme={null}
function buy(uint assetIn, uint minCoinOut) external returns (uint coinOut)
```

Buys Coin using PSM asset (only before immutability deadline). A time‑based buy fee may apply.

**Parameters:**

* `assetIn`: Amount of PSM asset to spend (in wei)
* `minCoinOut`: Minimum Coin amount to receive

**Returns:**

* `coinOut`: Amount of Coin received

**Requirements:**

* PSM must be configured
* Must be before immutability deadline
* `coinOut` must be ≥ `minCoinOut`

**Pricing:**

* Decimals conversion; buy fee ramps from 0→100 bps during the second half of the immutability window

***

### delegate

```solidity theme={null}
function delegate(address delegatee, bool isDelegatee) external
```

Delegates or revokes delegation rights for position management.

**Parameters:**

* `delegatee`: Address to grant/revoke delegation
* `isDelegatee`: True to grant, false to revoke

**Effects:**

* Allows delegatee to borrow and withdraw collateral via `adjust()` and call `setRedemptionStatus()` on behalf of delegator
* A delegator may assign multiple concurrent delegatees.
* Delegation can be changed at any time by delegator

***

### setRedemptionStatus

```solidity theme={null}
function setRedemptionStatus(address account, bool chooseRedeemable) external
```

Sets whether an account's position participates in redemptions (free debt) or accrues interest (paid debt).

**Parameters:**

* `account`: Address to set redemption status for (can be any address)
* `chooseRedeemable`: True to allow redemption, false to prevent

**Requirements:**

* Caller must be `account` or a delegated address

**Effects:**

* Toggles redeemable status. If true, borrower pays 0 interest. If false, borrowers pays variable rate.
* Default is non‑redeemable.

***

### accrueInterest

```solidity theme={null}
function accrueInterest() public
```

Accrues interest on paid debt. Called automatically by state‑changing functions and may be called directly.

**Effects:**

* Uses the shared InterestModel to compute current rate and interest
* Splits interest into fees (local/global reserves) and staking yield (minted to the Vault)
* Emits `InterestAccrued(interestAccrued, newBorrowRateMantissa)` on a successful accrual

***

### writeOff

```solidity theme={null}
function writeOff(address borrower, address to) external returns (bool writtenOff)
```

Writes off unrecoverable debt and socializes losses across all borrowers.

**Parameters:**

* `borrower`: Address with bad debt position
* `to`: Address to receive written-off collateral

**Returns:**

* `writtenOff`: True if debt was written off

**Requirements:**

* Oracle must allow liquidations
* Position must be extremely undercollateralized (debt > 100× collateral value)
* Callable by anyone (also attempted from `liquidate()` via try/catch)

**Effects:**

* Deletes borrower debt
* Redistributes it across free/paid pools proportionally
* Sends remaining collateral to `to`

## View Functions

### getDebtOf

```solidity theme={null}
function getDebtOf(address account) public view returns (uint debt)
```

Returns the current debt amount for an account, including accrued interest.

**Parameters:**

* `account`: Address to query debt for

**Returns:**

* `debt`: Current debt amount in wei

***

### getCollateralPrice

```solidity theme={null}
function getCollateralPrice() public view returns (uint price, bool reduceOnly, bool allowLiquidations)
```

Returns the normalized collateral price and safety flags.

**Returns:**

* `price`: Normalized to `36 - collateralDecimals` digits (never zero inside consumers)
* `reduceOnly`: True if only reductions allowed
* `allowLiquidations`: True if liquidations/redemptions/write‑offs permitted

***

### getFreeDebtRatio

```solidity theme={null}
function getFreeDebtRatio() public view returns (uint ratio)
```

Returns the current ratio of free debt to total debt (includes PSM assets in the free buffer).

**Returns:**

* `ratio`: Free debt ratio in basis points (0–10000)

***

### getSellAmountOut

```solidity theme={null}
function getSellAmountOut(uint coinIn) public view returns (uint assetOut)
```

Calculates the amount of PSM asset received for selling Coin (pure decimals conversion).

**Parameters:**

* `coinIn`: Amount of Coin to sell

**Returns:**

* `assetOut`: Amount of PSM asset received

***

### getBuyAmountOut

```solidity theme={null}
function getBuyAmountOut(uint assetIn) public view returns (uint coinOut, uint coinFee)
```

Calculates the amount of Coin and buy fee for buying with PSM asset (pre‑deadline).

**Parameters:**

* `assetIn`: Amount of PSM asset to spend

**Returns:**

* `coinOut`: Amount of Coin received
* `coinFee`: Fee amount deducted

***

### getFeedPrice

```solidity theme={null}
function getFeedPrice() external view returns (uint price, uint updatedAt)
```

Returns raw price feed data without protocol modifications.

**Returns:**

* `price`: Raw price from Chainlink feed
* `updatedAt`: Timestamp when price was last updated

## Protocol Management Functions

### setPendingOperator

```solidity theme={null}
function setPendingOperator(address _pendingOperator) external
```

Sets a new pending operator address (two‑step handoff).

**Parameters:**

* `_pendingOperator`: New operator address

**Requirements:**

* Caller must be current operator

***

### acceptOperator

```solidity theme={null}
function acceptOperator() external
```

Accepts operator role for pending operator.

**Requirements:**

* Caller must be pending operator

***

### setManager

```solidity theme={null}
function setManager(address _manager) external
```

Sets or updates the manager address (shared with operator for certain pre‑deadline actions).

**Parameters:**

* `_manager`: New manager address

**Requirements:**

* Caller must be operator or manager

***

### enableImmutabilityNow

```solidity theme={null}
function enableImmutabilityNow() external
```

Immediately enables immutability (locks certain configuration permanently).

**Requirements:**

* Caller must be operator
* Must be before immutability deadline

***

### pullLocalReserves

```solidity theme={null}
function pullLocalReserves() external
```

Mints accumulated local reserves to the caller (operator only).

**Requirements:**

* Caller must be operator

***

### pullGlobalReserves

```solidity theme={null}
function pullGlobalReserves(address _to) external returns (uint256 amount)
```

Mints accumulated global reserves to `_to` and returns the amount minted.

**Parameters:**

* `_to`: Address to receive reserves

**Returns:**

* `amount`: Amount of reserves minted

**Requirements:**

* Caller must be Factory

***

### reapprovePsmVault

```solidity theme={null}
function reapprovePsmVault() external
```

Reapproves the PSM vault for unlimited spending (before immutability deadline).

**Requirements:**

* Must be before immutability deadline

## Configuration Functions

### setHalfLife

```solidity theme={null}
function setHalfLife(uint64 halfLife) external
```

Sets the interest rate half-life for exponential decay and growth.

**Parameters:**

* `halfLife`: New half-life in seconds

**Requirements:**

* Caller must be operator or manager
* Must be before immutability deadline
* `halfLife` must be between 12 hours and 30 days

***

### setTargetFreeDebtRatio

```solidity theme={null}
function setTargetFreeDebtRatio(uint16 startBps, uint16 endBps) external
```

Sets the target free debt ratio range in basis points.

**Parameters:**

* `startBps`: Minimum free debt ratio (basis points)
* `endBps`: Maximum free debt ratio (basis points)

**Requirements:**

* Caller must be operator or manager
* Must be before immutability deadline
* `startBps` must be ≥500 and ≤ `endBps`
* `endBps` must be ≤9500

***

### setRedeemFeeBps

```solidity theme={null}
function setRedeemFeeBps(uint16 _redeemFeeBps) external
```

Sets the redemption fee in basis points.

**Parameters:**

* `_redeemFeeBps`: New redemption fee (basis points)

**Requirements:**

* Caller must be operator or manager
* Must be before immutability deadline
* `_redeemFeeBps` must be ≤500 (5%)

***

### setMaxBorrowDeltaBps

```solidity theme={null}
function setMaxBorrowDeltaBps(uint16 _maxBorrowDeltaBps) external
```

Sets the maximum acceptable rounding error for share-accounting conversions between debt and shares.

**Parameters:**

* `_maxBorrowDeltaBps`: New max rounding delta (basis points)

**Requirements:**

* Caller must be operator or manager
* Must be before immutability deadline
* `_maxBorrowDeltaBps` must be between 50 and 200 (0.5%–2%)

***

### setLocalReserveFeeBps

```solidity theme={null}
function setLocalReserveFeeBps(uint _feeBps) external
```

Sets the local reserve fee rate.

**Parameters:**

* `_feeBps`: New fee rate (basis points)

**Requirements:**

* Caller must be operator

***

## Key State Variables

### Debt accounting

* `totalPaidDebt` — cached total interest-bearing debt. May be missing accrued interest until `accrueInterest()` is called.
* `totalFreeDebt` — total non-interest-bearing (redeemable) debt.
* `totalPaidDebtShares`, `totalFreeDebtShares` — share-based accounting totals for the two debt pools.
* `freeDebtShares(address)`, `paidDebtShares(address)` — per-borrower shares in each pool.
* `isRedeemable(address)` — whether an account's debt is in redeemable (free) mode.
* `collateralBalances(address)` — per-borrower collateral in collateral-token decimals.

### Immutable deployment parameters

* `collateralFactor` — max LTV numerator in basis points (e.g., 8000 = 80%). Capped at 8500.
* `minDebt` — minimum debt per position (0 or ≥ this value).
* `stalenessThreshold` — oracle max staleness in seconds.
* `psmVaultMinTotalSupply` — PSM vault minimum supply required to enable buys (if `psmVault` set).
* `coin`, `collateral`, `vault`, `feed`, `psmAsset`, `psmVault`, `interestModel`, `factory` — contract references set at deployment.
* `immutabilityDeadline` — timestamp after which tunable parameters are locked.

### Tunable parameters (changeable by operator/manager before deadline)

* `redeemFeeBps` — redemption fee (max 500 / 5%).
* `maxBorrowDeltaBps` — share-accounting rounding tolerance (50–200).
* `targetFreeDebtRatioStartBps`, `targetFreeDebtRatioEndBps` — interest rate controller target band.
* `expRate` — exponential decay/growth rate derived from `halfLife`.
* `feeBps` — local reserve fee (operator-only; not protected by deadline).

### Reserves and governance

* `accruedLocalReserves`, `accruedGlobalReserves` — interest accrued to operator / fee recipient.
* `cachedGlobalFeeBps` — Factory fee rate cached at last accrual.
* `operator`, `pendingOperator`, `manager` — access-control addresses.

## Events

* `PositionAdjusted(address indexed account, int collateralDelta, int debtDelta)`
* `HalfLifeUpdated(uint64 halfLife)`
* `TargetFreeDebtRatioUpdated(uint16 startBps, uint16 endBps)`
* `RedeemFeeBpsUpdated(uint16 redeemFeeBps)`
* `MaxBorrowDeltaBpsUpdated(uint16 maxBorrowDeltaBps)`
* `DelegationUpdated(address indexed delegator, address indexed delegatee, bool isDelegatee)`
* `PendingOperatorUpdated(address indexed pendingOperator)`
* `OperatorAccepted(address indexed operator)`
* `ManagerUpdated(address indexed manager)`
* `LocalReserveFeeUpdated(uint256 feeBps)`
* `RedemptionStatusUpdated(address indexed account, bool isRedeemable)`
* `Liquidated(address indexed borrower, address indexed liquidator, uint repayAmount, uint collateralOut)`
* `WrittenOff(address indexed borrower, address indexed to, uint debt, uint collateral)`
* `Redeemed(address indexed account, address indexed borrower, uint amountIn, uint amountOut)`
* `Sold(address indexed account, uint coinIn, uint assetOut)`
* `Bought(address indexed account, uint assetIn, uint coinOut)`
* `ImmutabilityEnabled(uint256 timestamp)`
* `AccruedLocalReserves(uint256 amount)`
* `AccruedGlobalReserves(uint256 amount)`
* `InterestAccrued(uint256 interestAccrued, uint256 newBorrowRateMantissa)`