New to Universum? See the Universum (World Computer) White Paper!

Universum (Ruby Edition)

next generation ethereum 2.0 world computer runtime - run contract scripts / transactions in plain vanilla / standard ruby on the blockchain - update the (contract-protected / isolated) world states with plain vanilla / standard SQL


The Greeter - Your Digital Pal Who's Fun to Be With

Let's use the "Create a digital greeter" starter example from Ethereum to compare contracts in Solidity with contracts in Ruby:

pragma solidity >=0.4.22 <0.6.0;

contract Mortal {
    /* Define variable owner of the type address */
    address owner;

    /* This constructor is executed at initialization and sets the owner of the contract */
    constructor() public { owner = msg.sender; }

    /* Function to recover the funds on the contract */
    function kill() public { if (msg.sender == owner) selfdestruct(msg.sender); }

contract Greeter is Mortal {
    /* Define variable greeting of the type string */
    string greeting;

    /* This runs when the contract is executed */
    constructor(string memory _greeting) public {
        greeting = _greeting;

    /* Main function */
    function greet() public view returns (string memory) {
        return greeting;


# Greeter Contract

def setup( greeting )
  @owner    = msg.sender
  @greeting = greeting

def greet

def kill
  selfdestruct( msg.sender )  if msg.sender == @owner

(Source: contracts/greeter.rb)

And let's run the greeter with Universum (Uni):

require 'universum'

## create contract (english version)
tx = Uni.send_transaction( from: '0x1111', data: ['./greeter', 'Hello World!'] )
greeter = tx.receipt.contract

puts greeter.greet
#=> Hello World!

## create contract (spanish version)
tx = Uni.send_transaction( from: '0x1111', data: ['./greeter', '¡Hola, mundo!'] )
greeter_es = Receipt[ tx ].contract

puts greeter_es.greet
#=> ¡Hola, mundo!

puts greeter.greet
#=> Hello World!
puts greeter_es.greet
#=> ¡Hola, mundo!

The Coin - Minimum Viable Token

What's next? Let's use the "Create your own crypto-currency" example from Ethereum to compare contracts in Solidity with contracts in Ruby again:

pragma solidity >=0.4.22 <0.6.0;

contract MyToken {
    /* This creates an array with all balances */
    mapping (address => uint256) public balanceOf;

    /* Initializes contract with initial supply tokens to the creator of the contract */
        uint256 initialSupply
        ) public {
        balanceOf[msg.sender] = initialSupply;              // Give the creator all initial tokens

    /* Send coins */
    function transfer(address _to, uint256 _value) public returns (bool success) {
        require(balanceOf[msg.sender] >= _value);           // Check if the sender has enough
        require(balanceOf[_to] + _value >= balanceOf[_to]); // Check for overflows
        balanceOf[msg.sender] -= _value;                    // Subtract from the sender
        balanceOf[_to] += _value;                           // Add the same to the recipient
        return true;


## My Token Contract

def setup( initial_supply )
  @balance_of = Mapping.of( Address => Money )
  @balance_of[ msg.sender] = initial_supply

def transfer( to, value )
  assert @balance_of[ msg.sender ] >= value
  assert @balance_of[ to ] + value >= @balance_of[ to ]

  @balance_of[ msg.sender ] -= value
  @balance_of[ to ]         += value


(Source: contracts/mytoken.rb)

More Contract Samples

See the /universum-contracts collection.

More Documentation / Articles / Contracts

Programming Crypto Blockchain Contracts Step-by-Step Book / Guide - Let's start with ponzi & pyramid schemes. Run your own lotteries, gambling casinos and more on the blockchain world computer...

Safe Data Structures (Array, Hash, Struct) - Say goodbye to null / nil (and maybe) and the Billion-Dollar mistake. Say hello to zero and the Billon-Dollar fix.


Just install the gem:

$ gem install universum


The universum scripts are dedicated to the public domain. Use it as you please with no restrictions whatsoever.

Questions? Comments?

Send them along to the wwwmake forum. Thanks!