Experimental Technology

The Arkade Language is experimental technology in active development. All code and examples presented here are for exploration and proof of concept purposes only. Do not use in production environments.

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Arkade Syntax

Arkade Script uses a familiar syntax inspired by modern programming languages like Solidity, with specific adaptations for Bitcoin’s UTXO model. The syntax is designed to be readable and expressive while maintaining a close relationship to the underlying Bitcoin Script.

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Influences

Arkade Script’s syntax draws inspiration from several existing Bitcoin smart contracting languages:

  • CashScript: A high-level language for Bitcoin Cash smart contracts
  • Ivy: A smart contract language for Bitcoin
  • Solidity: The most widely used smart contract language (for Ethereum)

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Basic Structure

An Arkade Script contract consists of:

// Optional configuration options
options {
  server = serverPubkey;
  exit = 144; // Exit timelock in blocks
}

// Contract declaration with parameters
contract MyContract(
  pubkey user,
  pubkey server
) {
  // Function declarations (spending paths)
  function spend(signature userSig) {
    require(checkSig(userSig, user));
  }
}

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Comments

Arkade Script supports single-line and multi-line comments:

// This is a single-line comment

/*
  This is a
  multi-line comment
*/

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Options Block

The options block configures contract-wide settings:

options {
  // Server key parameter from contract parameters
  server = server;
  
  // Renewal timelock: 7 days (1008 blocks)
  renew = 1008;
  
  // Exit timelock: 24 hours (144 blocks)
  exit = 144;
}

Available options:

  • server: Specifies which parameter contains the server public key
  • renew: Specifies the renewal timelock in blocks
  • exit: Specifies the exit timelock in blocks

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Contract Declaration

Contracts are declared with a name and parameters:

contract MyContract(
  pubkey user,
  pubkey server,
  int timeoutBlocks,
  bytes32 hashValue
) {
  // Contract body
}

Parameters define the values needed to instantiate the contract and are accessible throughout the contract body.

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Functions

Functions define spending paths for the contract:

function spend(signature userSig) {
  require(checkSig(userSig, user));
}

Functions can be marked as internal to indicate they are helper functions and not spending paths:

function verifyCondition(bytes preimage, bytes32 hash) internal returns (bool) {
  return sha256(preimage) == hash;
}

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Variables and Assignments

Variables can be declared and assigned values:

int amount = 1000;
bytes message = sha256(timestamp + currentPrice + assetPair);
bool isValid = checkSig(userSig, user);

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Control Flow

Arkade Script supports if-else statements:

if (amount > threshold) {
  // Code for amounts above threshold
} else {
  // Code for amounts below or equal to threshold
}

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Expressions

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Arithmetic Operations

int sum = a + b;
int difference = a - b;
int product = a * b;
int quotient = a / b;
int remainder = a % b;

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Comparison Operations

bool isEqual = a == b;
bool isNotEqual = a != b;
bool isGreater = a > b;
bool isLess = a < b;
bool isGreaterOrEqual = a >= b;
bool isLessOrEqual = a <= b;

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Logical Operations

bool andResult = condition1 && condition2;
bool orResult = condition1 || condition2;
bool notResult = !condition;

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Bitwise Operations

int andResult = a & b;
int orResult = a | b;
int xorResult = a ^ b;
int notResult = ~a;
int leftShift = a << b;
int rightShift = a >> b;

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Require Statements

The require statement is used to enforce conditions:

require(amount > 0, "Amount must be positive");
require(checkSig(userSig, user), "Invalid signature");

If the condition is false, the script execution fails with the provided error message.

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Transaction Introspection

Arkade Script provides access to transaction data:

// Access transaction time
require(tx.time >= lockTime);

// Access outputs
require(tx.outputs[0].value == amount);
require(tx.outputs[0].scriptPubKey == script);

// Access inputs
require(tx.inputs[0].value == amount);
require(tx.inputs[0].scriptPubKey == script);

// Access the current input
require(tx.input.current.value == amount);
require(tx.input.current.scriptPubKey == script);

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Signature Verification

// Single signature verification
require(checkSig(userSig, user));

// Multi-signature verification
require(checkMultisig([user, admin], [userSig, adminSig]));

// Signature verification from stack
require(checkSigFromStack(oracleSig, oraclePk, message));

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Hash Functions

// SHA-256 hash
bytes32 hash = sha256(preimage);

// RIPEMD-160 hash
bytes20 hash = ripemd160(preimage);

// Hash160 (SHA-256 followed by RIPEMD-160)
bytes20 hash = hash160(preimage);

// Double SHA-256
bytes32 hash = hash256(preimage);

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Timelock Verification

// Absolute timelock
require(tx.time >= expirationTime);

// Relative timelock
require(tx.sequence >= relativeLockTime);

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Script Template

Arkade Script provides a built-in template for deriving the taproot output key:

bytes p2tr = new P2TR(internalKey, scriptTree);

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Error Handling

Arkade Script uses the require statement for error handling:

require(condition, "Error message");

If the condition is false, the script execution fails with the provided error message.

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Conclusion

This syntax reference provides an overview of Arkade Script’s language features. For more detailed information on specific language elements, refer to the following pages: