Installation | License | Usage
- It has high test coverage and uses solmate's high-precision fixed-point number arithmetic.
- It implement's ERC721's Metadata interface extension but it's not an ERC721. Wallets can hence still load any property like an ERC721 but detect that transfers shall be disabled.
- Implementing Harberger taxes as "deprecating licenses," this library structurally minimizes gas costs for sales.
With dapptools:
dapp install attestate/libharbergerOr foundry:
forge install attestate/libharberger
pragma solidity ^0.8.6;
import {Harberger, Period, Perwei} from "libharberger/Harberger.sol";
function tax() pure {
uint256 price = 1 ether;
Period period = Period(0, block.number);
Perwei taxRate = Perwei(1, 100) // == 0.01
uint256 nextPrice = Harberger.getNextPrice(taxRate, period, price);
//...
}An actual implementation of a Harberger tax would include charging a property
owner a tax rate periodically e.g. every month. In, let's say, the traditional
banking system: that'd mean the property owner transfers the tax in a
transaction monthly. The spiritual predecessor of this library
bin-studio/harberger-ads-contracts
indeed implemented a
collectTaxes
method that's supposed to be called periodically by the contract operator.
However, as since then gas prices on Ethereum mainnet have increased significantly and as periodically calling functions seems wastful, we're implementing the Harberger tax as a periodically reduced price value.
Say you buy property X for price p_x = 1 ether at block b_x, where x = 0,
then for each block b_x+1 we reduce p_x+1 by the tax rate. If say the tax
rate was t = 0.01, then property X price at block 1
b_1 is p_1 = 1 ether - 1 ether * 0.01 = 0.99 ether and at
b_2, p_2 = 0.99 ether - 0.99 ether * 0.01 = 0.9801 ether and so on.
We decrease the price in that way until it reaches zero, for when a new buyer
can buy the property for free. By taxing this way, we don't need to
periodically call a collectTaxes method.
- Rename
Percentagestruct toPerwei - Add further tests to confirm precision of up to 18 decimal points
NOTE: We only noticed now that between 0.0.1 and 0.2.0, we've made a mistake in semantic versioning as "0.2.0" should actually be "0.1.0". But we're deciding to stick with the mistake and we'll try to properly produce ascending numbers in the future.
- Simplify pricing mechanism
- Initial release
See LICENSE file.