State Machine

Blockchain development can be model as a State Machine.

The set of all the functions deployed on chain is the State Transfer Function (STF) of a State Machine.

The State Machine comes with the basic concepts, an Input is applied to the Current State, under the rule of State Transfer Function to transit the Current State into a New State.

State Machine

Here is an example, let's assume we have a Current State of block number 100:

{
   Alice's USDC Balace: 50,
   Bob's USDC Balace: 200,
}

While in the block 100, Bob is sending a transaction to move USDC balance from Bob to Alice:

{"p": "zen", "f": "transfer", "a": ["USDC", "Alice", 100]}

The transfer function is accepting the transaction as the Input of State Machine, outputs a New State:

{
   Alice's USDC Balace: 150,
   Bob's USDC Balace: 100,
}

As an example, we can take a look how the transfer STF is written in python:

def transfer(info, args):
    sender = info['sender']
    tick = args['a'][0]
    receiver = args['a'][1].lower()
    value = int(args['a'][2])
    assert value > 0

    sender_balance = get(tick, 'balance', 0, addr)
    assert sender_balance >= value
    sender_balance -= value
    put(addr, tick, 'balance', sender_balance, addr)
    receiver_balance = get(tick, 'balance', 0, receiver)
    receiver_balance += value
    put(receiver, tick, 'balance', receiver_balance, receiver)

This is a very basic function, we use get and put API calls here. For the security reason, we should do more check for the arguments.