02 hello smart contracts
- 1. Hello Smart Contracts Dr. Bastian Blankenburg, UTU Technologies Limited Nairobi, October 2018
- 2. Outline 1. Recap: DLTs and d-apps 2. Æternity (online) tools to get started 3. Smart Contract Language Sophia
- 3. Recap: DLTs and d-apps Part 1
- 4. Blockchain: a Distributed Ledger Technology Source: Blockchain technology. Legislative Council of the Hong Kong Special Administrative Region, 2015, http://www.legco.gov.hk/research-publications/english/essentials-1516ise15-blockchain-technology.htm, original source given: Oliver Wyman (2015) • Ledger: history of transactions. • Examples: Bank account, land registry, Facebook, any classical database Centralised ledger Distributed ledger
- 5. Byzantine Generals Problem Source: https://medium.com/@sardorislomov/what-is-byzantine-generals-problem-1f436b49bc23
- 6. Byzantine Generals Problem Source: https://medium.com/@sardorislomov/what-is-byzantine-generals-problem-1f436b49bc23
- 7. Decentralised Application (d-app) Source: A Decentralised Sharing App running a Smart Contract on the Ethereum Blockchain, Bogner et al., IOT, 2016
- 8. Æternity (online) tools to get started Part 2
- 9. Æternity Local Test Net (1) 1. Prerequisites: 1. git 2. Docker: http://docker.com/ 3. node.js (for Python see https://github.com/aeternity/aepp-sdk-python, https:// forum.aeternity.com/t/tutorial-for-the-test-network-step-by-step-and-improvement/864) 2. Clone Epoch v0.22.0: https://github.com/aeternity/epoch/tree/v0.22.0 3. Install the JS SDK: in a new project directory: npm install aeternity/aepp-sdk#develop 4. In the epoch directory, start local test net: docker-compose up —build
- 10. Æternity Local Test Net (2) 1. Create a wallet: node node_modules/.bin/aecli account -f -H http://localhost:3001 create ./wallet ( if this gives an error, try cd ‘node_modules/@aeternity/aepp-sdk’; npm install ) 2. In the epoch directory, 1. docker-compose down 2. Copy+paste the public key (“ak_…”) from your wallet in the project directory to the “mining: beneficiary:” setting in docker/epoch_node?_mean16 3. docker-compose up —build 3. In the project directory, check your balance: node node_modules/.bin/aecli account -f -H http://localhost:3001 balance ./wallet
- 11. Æternity Local Test Net (3) 1. Copy + paste the example contract from https://contracts.aepps.com into test.sophia in your project directory. 2. Deploy the contract: node node_modules/.bin/aecli contract --host http://localhost:3001 deploy ./wallet test.sophia 3. Review the deploy descriptor 4. Get contract code from the chain: curl -v http://localhost:3001/v2/contracts/<address>/code 5. Locally compile the contract again to verify it’s the same: node node_modules/.bin/aecli contract --host http://localhost:3001 compile test.sophia
- 12. Smart Contract Language Sophia Part 3
- 13. Imperative vs Functional Source: http://happihacking.com/aeternity/webinar20180822/
- 15. The Sophia Language 1. https://github.com/aeternity/protocol/blob/master/contracts/sophia.md 2. Example: free-for-all account: contract Test = record state = {balance : int} public function init() : state = {balance = 0} public stateful function add(amount: int) = put(state{balance @ b = b + amount}) public function getBalance() = state.balance public stateful function withdraw(amount: int) = if(amount < state.balance) put(state{balance @ b = b - amount}) amount else 0
- 16. The Sophia Language Exercise: 1. Use actual tokens transfer instead of just assigning ints 2. Everybody has their own balance and add, getBalance and withdraw work only for the caller’s balance.
- 17. More Æternity Resources 1. Online tools 1. https://contracts.aepps.com 2. https://explorer.aepps.com 3. See also https://blog.aeternity.com/aepps-update-smart-contract- development-96241f65b07d 2. Developer resources 1. For an overview: aepps.com 2. Hands on: dev.aepps.com 3. Safe time & collaborate: https://github.com/aeternity/aepp-components 4. Support: forum.aeternity.com 5. aeternity.com
- 18. Thank you!