pTokens
Introduction
Each asset supported by the Paribus Protocol is integrated through a pToken contract, which is an EIP-20 compliant representation of balances supplied to the protocol. By minting pTokens, users (1) earn interest through the pToken's exchange rate, which increases in value relative to the underlying asset, and (2) gain the ability to use pTokens as collateral.
pTokens are the primary means of interacting with the Paribus Protocol; when a user mints, redeems, borrows, repays a borrow, liquidates a borrow, or transfers pTokens, she will do so using the pToken contract.
There are currently two types of pTokens: PErc20 and PEther. Though both types expose the EIP-20 interface, PErc20 wraps an underlying ERC-20 asset, while PEther simply wraps Ether itself. As such, the core functions which involve transferring an asset into the protocol have slightly different interfaces depending on the type, each of which is shown below.
Mint
The mint function transfers an asset into the protocol, which begins accumulating interest based on the current Supply Rate for the asset. The user receives a quantity of pTokens equal to the underlying tokens supplied, divided by the current Exchange Rate.
PErc20
msg.sender
: The account which shall supply the asset, and own the minted pTokens.mintAmount
: The amount of the asset to be supplied, in units of the underlying asset.RETURN
: 0 on success, otherwise an Error code Before supplying an asset, users must first approve the pToken to access their token balance.
PEther
msg.value
: The amount of ether to be supplied, in wei.msg.sender
: The account which shall supply the ether, and own the minted pTokens.RETURN
: No return, reverts on error.
Solidity
Web3 1.0
Redeem
The redeem function converts a specified quantity of pTokens into the underlying asset, and returns them to the user. The amount of underlying tokens received is equal to the quantity of pTokens redeemed, multiplied by the current Exchange Rate. The amount redeemed must be less than the user's Account Liquidity and the market's available liquidity.
PErc20 / PEther
msg.sender
: The account to which redeemed funds shall be transferred.redeemTokens
: The number of pTokens to be redeemed.RETURN
: 0 on success, otherwise an Error code
Solidity
Web3 1.0
Redeem Underlying
The redeem underlying function converts pTokens into a specified quantity of the underlying asset, and returns them to the user. The amount of pTokens redeemed is equal to the quantity of underlying tokens received, divided by the current Exchange Rate. The amount redeemed must be less than the user's Account Liquidity and the market's available liquidity.
PErc20 / PEther
msg.sender
: The account to which redeemed funds shall be transferred.redeemAmount
: The amount of underlying to be redeemed.RETURN
: 0 on success, otherwise an Error code
Solidity
Web3 1.0
Borrow
The borrow function transfers an asset from the protocol to the user, and creates a borrow balance which begins accumulating interest based on the Borrow Rate for the asset. The amount borrowed must be less than the user's Account Liquidity and the market's available liquidity. To borrow Ether, the borrower must be 'payable' (solidity).
PErc20 / PEther
msg.sender
: The account to which borrowed funds shall be transferred.borrowAmount
: The amount of the underlying asset to be borrowed.RETURN
: 0 on success, otherwise an Error code
Solidity
Web3 1.0
Repay Borrow
The repay function transfers an asset into the protocol, reducing the user's borrow balance.
PErc20
msg.sender
: The account which borrowed the asset, and shall repay the borrow.repayAmount
: The amount of the underlying borrowed asset to be repaid. A value of -1 (i.e.2^256
- 1) can be used to repay the full amount.RETURN
: 0 on success, otherwise an Error code Before repaying an asset, users must first approve the pToken to access their token balance.
PEther
msg.value
: The amount of ether to be repaid, in wei.msg.sender
: The account which borrowed the asset, and shall repay the borrow.RETURN
: No return, reverts on error.
Solidity
Web3 1.0
Repay Borrow Behalf
The repay function transfers an asset into the protocol, reducing the target user's borrow balance.
PErc20
msg.sender
: The account which shall repay the borrow.borrower
: The account which borrowed the asset to be repaid.repayAmount
: The amount of the underlying borrowed asset to be repaid. A value of -1 (i.e.2^256
- 1) can be used to repay the full amount.RETURN
: 0 on success, otherwise an Error code Before repaying an asset, users must first approve the pToken to access their token balance.
PEther
msg.value
: The amount of ether to be repaid, in wei.msg.sender
: The account which shall repay the borrow.borrower
: The account which borrowed the asset to be repaid.RETURN
: No return, reverts on error.
Solidity
Web3 1.0
Transfer
Transfer is an ERC-20 method that allows accounts to send tokens to other Ethereum addresses. A pToken transfer will fail if the account has entered that pToken market and the transfer would have put the account into a state of negative liquidity.
PErc20 / PEther
recipient
: The transfer recipient address.amount
: The amount of pTokens to transfer.RETURN
: Returns a boolean value indicating whether or not the operation succeeded.
Solidity
Web3 1.0
Liquidate Borrow
A user who has negative account liquidity is subject to liquidation by other users of the protocol to return his/her account liquidity back to positive (i.e. above the collateral requirement). When a liquidation occurs, a liquidator may repay some or all of an outstanding borrow on behalf of a borrower and in return receive a discounted amount of collateral held by the borrower; this discount is defined as the liquidation incentive. A liquidator may close up to a certain fixed percentage (i.e. close factor) of any individual outstanding borrow of the underwater account. Unlike in v1, liquidators must interact with each pToken contract in which they wish to repay a borrow and seize another asset as collateral. When collateral is seized, the liquidator is transferred pTokens, which they may redeem the same as if they had supplied the asset themselves. Users must approve each pToken contract before calling liquidate (i.e. on the borrowed asset which they are repaying), as they are transferring funds into the contract.
PErc20
msg.sender
: The account which shall liquidate the borrower by repaying their debt and seizing their collateral.borrower
: The account with negative account liquidity that shall be liquidated.repayAmount
: The amount of the borrowed asset to be repaid and converted into collateral, specified in units of the underlying borrowed asset.pTokenCollateral
: The address of the pToken currently held as collateral by a borrower, that the liquidator shall seize.RETURN
: 0 on success, otherwise an Error code Before supplying an asset, users must first approve the pToken to access their token balance.
PEther
msg.value
: The amount of ether to be repaid and converted into collateral, in wei.msg.sender
: The account which shall liquidate the borrower by repaying their debt and seizing their collateral.borrower
: The account with negative account liquidity that shall be liquidated.pTokenCollateral
: The address of the pToken currently held as collateral by a borrower, that the liquidator shall seize.RETURN
: No return, reverts on error.
Solidity
Web3 1.0
Key Events
Error Codes
Failure Info
Exchange Rate
Each pToken is convertible into an ever increasing quantity of the underlying asset, as interest accrues in the market. The exchange rate between a pToken and the underlying asset is equal to:
PErc20 / PEther
RETURN
: The current exchange rate as an unsigned integer, scaled by 1 * 10^(18 - 8 + Underlying Token Decimals).
Solidity
Web3 1.0
Tip: note the use of call
vs. send
to invoke the function from off-chain without incurring gas costs.
Get Cash
Cash is the amount of underlying balance owned by this pToken contract. One may query the total amount of cash currently available to this market.
PErc20 / PEther
RETURN
: The quantity of underlying asset owned by the contract.
Solidity
Web3 1.0
Total Borrows
Total Borrows is the amount of underlying currently loaned out by the market, and the amount upon which interest is accumulated to suppliers of the market.
PErc20 / PEther
RETURN
: The total amount of borrowed underlying, with interest.
Solidity
Web3 1.0
Borrow Balance
A user who borrows assets from the protocol is subject to accumulated interest based on the current borrow rate. Interest is accumulated every block and integrations may use this function to obtain the current value of a user's borrow balance with interest.
PErc20 / PEther
account
: The account which borrowed the assets.RETURN
: The user's current borrow balance (with interest) in units of the underlying asset.
Solidity
Web3 1.0
Borrow Rate
At any point in time one may query the contract to get the current borrow rate per block.
PErc20 / PEther
RETURN
: The current borrow rate as an unsigned integer, scaled by 1e18.
Solidity
Web3 1.0
Total Supply
Total Supply is the number of tokens currently in circulation in this pToken market. It is part of the EIP-20 interface of the pToken contract.
PErc20 / PEther
RETURN
: The total number of tokens in circulation for the market.
Solidity
Web3 1.0
Underlying Balance
The user's underlying balance, representing their assets in the protocol, is equal to the user's pToken balance multiplied by the Exchange Rate.
PErc20 / PEther
account
: The account to get the underlying balance of.RETURN
: The amount of underlying currently owned by the account.
Solidity
Web3 1.0
Supply Rate
At any point in time one may query the contract to get the current supply rate per block. The supply rate is derived from the borrow rate, reserve factor and the amount of total borrows.
PErc20 / PEther
RETURN
: The current supply rate as an unsigned integer, scaled by 1e18.
Solidity
Web3 1.0
Total Reserves
Reserves are an accounting entry in each pToken contract that represents a portion of historical interest set aside as cash which can be withdrawn or transferred through the protocol's governance. A small portion of borrower interest accrues into the protocol, determined by the reserve factor.
PErc20 / PEther
RETURN
: The total amount of reserves held in the market.
Solidity
Web3 1.0
Reserve Factor
The reserve factor defines the portion of borrower interest that is converted into reserves.
PErc20 / PEther
RETURN
: The current reserve factor as an unsigned integer, scaled by 1e18.
Solidity
Web3 1.0
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