Contracting

Quickstart

1. Install

2. Create Your First Smart Contract

#create some state 
balances = Hash(default_value=0) 

#seed initial balances 
@construct 
def seed(): 
  balances['me'] = 1000000 

#transfer the caller's funds to another account
@export
def transfer(amount: float, to: str):
  assert amount > 0, 'Cannot send negative balances!'
  assert balances[ctx.caller] >= amount, 'Insufficient Funds to send!'

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

# give permission to the spender to spend your funds
@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 someone's funds to another account
@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
                  

3. Upload Your First Contact To The Blockchain

Open your lamden wallet and select the 'Smart Contract' section

Click on the button 'Submit to Network'

Simply press button 'Confirm Transaction'

4. Interact With The Block Service To Access Your Contract Data

Open shell and then run the following command:

curl http://165.22.47.195:3535/contracts/con_my_first_contract

Then you will get the source code of your contract and other relevant information

{
   "con_my_first_contract": {
      "__code__": "__balances = Hash(default_value=0, contract='con_my_first_contract', name=\n    'balances')......",
      "__compiled__": {
         "__bytes__": "e3000000000000000000000......"
      },
      "__developer__": "b17eabddbd474bdaebfca71f654ab7dc1195510062e3cdbbdc442a028b050e41",
      "__owner__": null,
      "__submitted__": {
         "__time__": [
            2022,
            6,
            9,
            16,
            26,
            34,
            0
         ]
      },
      "balances": {
         "me": 1000000
      }
   }
}