Example of a Vyper rebase token.
# pragma version ^0.4.0
# Rebase token (compound interest rate)
RAY: constant(uint256) = 10**27
MIN_R: constant(uint256) = 10**25
authorized: public(HashMap[address, bool])
pie: public(uint256)
slices: public(HashMap[address, uint256])
rate: public(uint256)
acc: public(uint256)
t: public(uint256)
@deploy
def __init__():
self.authorized[msg.sender] = True
self.rate = RAY
self.acc = RAY
self.t = block.timestamp
@external
def set_rate(ray: uint256):
assert self.authorized[msg.sender]
assert self.t == block.timestamp
self.rate = ray
@internal
@view
def r() -> uint256:
n: uint256 = (block.timestamp - self.t)
if n > 0:
rate: uint256 = self.rate
if rate > RAY:
# rate = 1 + x
x: uint256 = rate - RAY
# binomial expansion
# (1+x)^n = 1 + n*x + (n*(n-1)/2*x^2) + (n*(n-1)*(n-2)/(2*3)*x^3) + ...
x1: uint256 = n * x
x2: uint256 = x1 * ((n - 1) if n > 1 else 0) // 2 * x // RAY
x3: uint256 = x2 * ((n - 2) if n > 2 else 0) // 3 * x // RAY
return RAY + x1 + x2 + x3
elif rate < RAY:
# rate = 1 - x
x: uint256 = RAY - rate
# binomial expansion
# (1-x)^n = 1 - n*x + (n*(n-1)/2*x^2) - (n*(n-1)*(n-2)/(2*3)*x^3) + ...
x1: uint256 = n * x
x2: uint256 = x1 * ((n - 1) if n > 1 else 0) // 2 * x // RAY
x3: uint256 = x2 * ((n - 2) if n > 2 else 0) // 3 * x // RAY
# Check underflow and min
# RAY - x1 + x2 - x3 <= MIN_R
if RAY + x2 < MIN_R + x1 + x3:
return MIN_R
return RAY - x1 + x2 - x3
else:
return RAY
return RAY
@internal
@view
def a() -> uint256:
return self.acc * self.r() // RAY
@external
@view
def total_supply() -> uint256:
return self.pie * self.a() // RAY
@external
@view
def balance_of(usr: address) -> uint256:
return self.slices[usr] * self.a() // RAY
@external
def poke():
self.acc *= self.r() // RAY
self.t = block.timestamp
@external
def mint(dst: address, amt: uint256):
assert self.authorized[msg.sender]
assert self.t == block.timestamp
a: uint256 = self.acc
s: uint256 = amt * RAY // a
assert s > 0
self.slices[dst] += s
self.pie += s
@external
def burn(amt: uint256):
if amt == max_value(uint256):
self.pie -= self.slices[msg.sender]
self.slices[msg.sender] = 0
else:
assert self.t == block.timestamp
a: uint256 = self.acc
s: uint256 = amt * RAY // a
assert s > 0
self.pie -= s
self.slices[msg.sender] -= s
@external
def transfer(dst: address, amt: uint256):
if amt == max_value(uint256):
self.slices[dst] += self.slices[msg.sender]
self.slices[msg.sender] = 0
else:
assert self.t == block.timestamp
a: uint256 = self.acc
s: uint256 = amt * RAY // a
self.slices[msg.sender] -= s
self.slices[dst] += s
