Programming Languages × Blockchains Vlad Ki ESM.one 

Mainstream PLs won't work 

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DApps in 2013 

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DApps in 2018 

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function createGen0Auction(uint256 _genes) public onlyCOO { require(gen0CreatedCount < gen0CreationLimit); uint256 kittyId = _createKitty(0, 0, 0, _genes, address(this)); _approve(kittyId, saleAuction); saleAuction.createAuction(kittyId, _computeNextGen0Price(), 0, gen0AuctionDuration, address(this)); gen0CreatedCount++; } function _computeNextGen0Price() internal view returns (uint256) { uint256 avePrice = saleAuction.averageGen0SalePrice(); require(avePrice < 340282366920938463463374607431768211455); uint256 nextPrice = avePrice + (avePrice / 2); if (nextPrice < gen0StartingPrice) { nextPrice = gen0StartingPrice; } return nextPrice; } 

#!/bin/bash while { echo -ne "HTTP/1.1 200 OK\r\nConnection: close\r\n\r\nlol\r\n"; } \ | nc -l 80 do : done 

WTF?! 

Developers are losing abstractions! 

ACID Atomic Consistent Isolated Durable 

BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE; UPDATE accounts SET balance = balance + 100 WHERE addr = 0x4206f95fc533483; UPDATE accounts SET balance = balance - 100 WHERE addr = 0x083c41ea13af6c2; COMMIT; 

SELECT address FROM accounts ORDER BY random() LIMIT 1; 

CREATE SEQUENCE txn; BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE; INSERT INTO tx VALUES (nextval('txn'), current_timestamp); INSERT INTO tx VALUES (nextval('txn'), current_timestamp); COMMIT; 

BASE Basically Available Soft State Eventually Consistent 

http:/ /docs.basho.com/riak/kv/2.2.3/learn/concepts/clusters/ 

$ curl http://riak/buckets/chain/keys/0x4206f95fc533483 < HTTP/1.1 300 Multiple Choices < X-Riak-Vclock: a85hYGDgyGDKBVIszMk55zKYEhnzWBlKIniO8kGF2TyvHYIKf0cIszUnMTBz HYVKbIhEUl+VK4spDFTPxhHzFyqhEoVQz7wkSAGLMGuz6FSocFIUijE3pt5H lsgCAA== < Content-Type: multipart/mixed; boundary=lol --lol Content-Type: application/json Link: ; rel="up" Etag: 16vic4eU9ny46o4KPiDz1f Last-Modified: Wed, 10 Mar 2010 18:01:06 GMT 100 --lol Content-Type: application/json Link: ; rel="up" Etag: 4v5xOg4bVwUYZdMkqf0d6I Last-Modified: Wed, 10 Mar 2010 18:00:04 GMT 200 

Logical Clocks https:/ /cacm.acm.org/magazines/2016/4/200168-why-logical-clocks-are-easy/abstract 

https:/ /hal.inria.fr/file/index/docid/555588/filename/techreport.pdf 

Definition counter : Type := nat * nat. Definition zero := (O, O). Definition succ (c : counter) := match c with (p, n) => (p + 1, n) end. Definition pred (c : counter) := match c with (p, n) => (p, n + 1) end. 

$ curl -XPOST http://riak/types/counters/buckets/ chain/datatypes/0x4206f95fc533483 \ -d '{"increment": 100}' $ curl -XPOST http://riak/types/counters/buckets/ chain/datatypes/0x4206f95fc533483 \ -d '{"decrement": 50}' $ curl http://riak/types/counters/buckets/chain/ datatypes/0x4206f95fc533483 {"type":"counter", "value": 100} 

В риаке конфликты на чтение Пиши в блокчейн! А зачем? Глобальный консенсус! Так языка запросов даже нет! Ты чё, пёс, это же крипта! 

UTXO Unconvincing Transaction Outcome 

Smart Contracts Smart contracts help you exchange money, property, shares, or anything of value in a transparent, conflict-free way while avoiding the services of a middleman. 

european :: Date -> Contract -> Contract european t u = at t (u `or` zero) 

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Smart Contracts Smart contracts are executable programs run on top of an immutable distributed database whose inputs and outputs are maintained globally consistent by a distributed consensus protocol. 

pragma solidity ^0.4.0; contract SimpleStorage { uint storedData; function set(uint x) public { storedData = x; } function get() public constant returns (uint) { return storedData; } } 

function createGen0Auction(uint256 _genes) public onlyCOO { require(gen0CreatedCount < gen0CreationLimit); uint256 kittyId = _createKitty(0, 0, 0, _genes, address(this)); _approve(kittyId, saleAuction); saleAuction.createAuction(kittyId, _computeNextGen0Price(), 0, gen0AuctionDuration, address(this)); gen0CreatedCount++; } function _computeNextGen0Price() internal view returns (uint256) { uint256 avePrice = saleAuction.averageGen0SalePrice(); require(avePrice < 340282366920938463463374607431768211455); uint256 nextPrice = avePrice + (avePrice / 2); if (nextPrice < gen0StartingPrice) { nextPrice = gen0StartingPrice; } return nextPrice; } 

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web3.eth.getTransaction('0x9fc76417374aa880d4449a1f7f31ec5 97f00b1f6f3dd2d66f4c9c6c445836d8b§234') .then(console.log); > { "hash": "0x9fc76417374aa880d4449a1f7f31ec597f00b1f6f3dd2d66f4c9c6c 445836d8b", "nonce": 2, "blockHash": "0xef95f2f1ed3ca60b048b4bf67cde2195961e0bba6f70bcbea9a2c4e 133e34b46", "blockNumber": 3, "transactionIndex": 0, "from": "0xa94f5374fce5edbc8e2a8697c15331677e6ebf0b", "to": "0x6295ee1b4f6dd65047762f924ecd367c17eabf8f", "value": '123450000000000000', "gas": 314159, "gasPrice": '2000000000000', "input": "0x57cb2fc4" } 

Why? 

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ERC20 allowance contract ERC20 is ERC20Basic { function transferFrom(address from, address to, uint256 value) public returns (bool); function approve(address spender, uint256 value) public returns (bool); } https:/ /docs.google.com/document/d/ 1YLPtQxZu1UAvO9cZ1O2RPXBbT0mooh4DYKjA_jp-RLM/edit https:/ /github.com/ethereum/EIPs/blob/master/EIPS/eip-20.md 

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Ensure Properties! 

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Coq Dependent Type Theory Tactics Extraction to OCaml and Haskell Formalization of mathematics 

Theorem pred_and_succ_covariant: forall c: counter, pred (succ c) = succ (pred c). intros c. induction c. compute. reflexivity. Qed. 

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pragma solidity ^0.4.0; contract Fund { mapping(address => uint) shares; function withdraw() public { if (msg.sender.call.value(shares[msg.sender])()) shares[msg.sender] = 0; } } 

The DAO https:/ /abhiroop.github.io/Exceptions-and-Transactions/ 

Interface State Machine Plutus Plutus Core Solidity EVM (stack) IELE (register) Chain Bitcoin Script Ivy Vyper 

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Hardening Strategies Interfaces (*.h, *.mli) Interfaces + property claims (f . g = g . f) Interfaces + property proofs Implementation property claims Implementation property proofs 

Hardening Strategies End-to-end compilation Verify interfaces in Coq Use plutus core/iele as compilation targets 

Contracts as State Machines 

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Denotate to simple languages! 

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System F 

Turing vs Church 

Interface State Machine Plutus Plutus Core Solidity EVM (stack) IELE (register) Chain Bitcoin Script Ivy Vyper 

Interface State Machine Plutus Plutus Core Solidity EVM (stack) IELE (register) Chain Bitcoin Script Ivy Vyper run . compile = meaning 

Gotcha 

gcd :: (Integral a) => a -> a -> a gcd x y = gcd' (abs x) (abs y) where gcd' a 0 = a gcd' a b = gcd' b (a `rem` b) 

Lemma euclid_rec : forall v3 : Z, (0 <= v3)%Z -> forall u1 u2 u3 v1 v2 : Z, (u1 * a + u2 * b)%Z = u3 -> (v1 * a + v2 * b)%Z = v3 -> (forall d : Z, gcd u3 v3 d -> gcd a b d) -> Euclid. Proof. intros v3 Hv3; generalize Hv3; pattern v3 in |- *. apply Z_lt_rec. clear v3 Hv3; intros. elim (Z_zerop x); intro. apply Euclid_intro with (u := u1) (v := u2) (d := u3). assumption. apply H2. rewrite a0; auto. set (q := (u3 / x)%Z) in *. assert (Hq : (0 <= u3 - q * x < x)%Z). replace (u3 - q * x)%Z with (u3 mod x)%Z. apply Z_mod_lt; omega. assert (xpos : (x > 0)%Z). omega. generalize (Z_div_mod_eq u3 x xpos). unfold q in |- *. intro eq; pattern u3 at 2 in |- *; rewrite eq; ring. apply (H (u3 - q * x)%Z Hq (proj1 Hq) v1 v2 x (u1 - q * v1)%Z (u2 - q * v2)%Z). tauto. replace ((u1 - q * v1) * a + (u2 - q * v2) * b)%Z with (u1 * a + u2 * b - q * (v1 * a + v2 * b))%Z. rewrite H0; rewrite H1; trivial. ring. intros; apply H2. apply gcd_for_euclid with q; assumption. assumption. Qed. 

twitter.com/kievfprog kievfprog.net 

Haskell Rust Scala F# F* Ur Agda Idris Coq SML OCaml QuickCheck SMT 

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Yay Formal Methods! [email protected]