LST001 - Basic Token Interface v1.0 (approved)

Goal

This standard will describe the variables and methods needed to create a basic token on the Lamden Blockchain. Adherence to this standard ensures highest possible compatibility for your token.

Changes

Discussion on finalizing this standard is taking place in the Github Discussions; With a current deadline of March 2nd, 2021. Anyone is welcome to join and comment.

Imports

none

Variables

balances

This variable holds the main account balances for the contract balances[account]. It also uses a multi-hash to store allowances balances[owner, spender].

Type: Hash
- default value: 0
Required: True

balances = Hash(default_value=0)

Methods

seed

This is the constructor method for smart contract. We will use it to mint an initial token supply.

This method is not required. The below example is included to show how you might mint an initial supply to an account.

Decorator: @construct
Required: False
Public: False
arguments:
- vk
  - type: string
  - description: The account provided will be minted the initial supply of tokens.
state changes: 1
assertions: none
return: void

@construct
def seed(vk: str):
    balances[vk] = 1_000_000

transfer

This is the main transfer method for the token. This should only be called if the caller is sending their tokens directly. To send tokens on behalf of another account use the transfer_from method.

Decorator: @export
Public: True
arguments:
- amount
  - type: float
  - The amount of tokens to be transferred
- to
  - type: string
  - The account to send the tokens to.
state changes: 2
assertions:
- amount must be greater-than 0
  - error: Cannot send negative balances!
- callers token balance must be greater-than or equal to amount
  - error: Not enough coins to send!
return: void

@export
def transfer(amount: float, to: str):
    assert amount > 0, 'Cannot send negative balances!'
    assert balances[ctx.caller] >= amount, 'Not enough coins to send!'

    # remove amount from senders account
    balances[ctx.caller] -= amount
    # add amount to receivers account
    balances[to] += amount

approve

This method will return add to the approval balance of the caller's account for the to address provided.

Decorator: @export
Public: True
arguments:
- amount
  - type: float
  - The amount of approval to add to the to account
- to
  - type: string
  - The account that will receive the approval amount
state changes: 2
assertions:
- amount must be greater-than 0
  - error: Cannot send negative balances!
return: void

@export
def approve(amount: float, to: str):
    assert amount > 0, 'Cannot send negative balances!'

    # Add the amount to the callers
    balances[ctx.caller, to] += amount

transfer_from

This method will allow a caller to spend tokens from another account. For this to work a prior call to approve is needed by the main_account to set an allowance for the caller. Failure to set an allowance beforehand will cause the method to error.

Decorator: @export
Public: True
arguments:
- amount
  - type: float
  - The amount of tokens to transfer from main_account
- to
  - type: string
  - The account that the tokens will be sent to
- main_account
  - type: string
  - The account the tokens will taken from
state changes: 3
assertions:
- amount must be greater-than 0
  - error: Cannot send negative balances!
- caller has an approval greater-than or equal to the transfer amount
  - error: Not enough coins approved to send! You have X and are trying to spend X
- the token balance of main_account is greater-than or equal to the transfer amount
  - error: Not enough coins to send!
return: void

@export
def transfer_from(amount: float, to: str, main_account: str):
    assert amount > 0, 'Cannot send negative balances!'

    assert balances[main_account, ctx.caller] >= amount, 'Not enough coins approved to send! You have {} and are trying to spend {}'\
        .format(balances[main_account, ctx.caller], amount)
    assert balances[main_account] >= amount, 'Not enough coins to send!'

    # reduce the approval amount by the amount being spent
    balances[main_account, ctx.caller] -= amount

    # remove amount spent from the main account
    balances[main_account] -= amount
    # add the amount spent to the receivers account
    balances[to] += amount

Lamden-Standards/LST001