Smart Contracts Without Ethereum: The Idea Behind Programmable Money

When we think of smart contracts, we often think of Ethereum. But the core idea — code that runs on a blockchain — isn't limited to Ethereum at all.

In this article, we'll:

  • Demystify what smart contracts are
  • Show how the idea can work even in a simple blockchain
  • Implement a basic programmable transaction system in Go

Let’s dive into what makes a contract "smart" — and how we can simulate one without needing Solidity or the Ethereum Virtual Machine.

What Is a Smart Contract?

At its core, a smart contract is a self-executing program stored on the blockchain that runs when certain conditions are met.

Think of it as:

  • Code + Rules + Money
  • “If this happens, then do that — automatically and immutably.”

Examples:

  • Escrow: Funds are released only if both parties approve.
  • Crowdfunding: If a funding goal is met, transfer money; if not, refund.
Our Goal: Simple Smart Contracts in Go

Instead of deploying to Ethereum, we’ll:

  • Simulate a blockchain that holds "accounts" with balances.
  • Let users define transactions with embedded rules (our mini-contracts).
  • Execute and verify those rules before applying changes.

This is enough to grasp the essence of smart contracts: programmable, verifiable conditions on transactions.

Go example

package main

import (
  "fmt"
)

// A programmable transaction
type Transaction struct {
  From   string
  To     string
  Amount int
  Rule   func(state *State) bool // Contract condition
}

// Global account state
type State struct {
  Balances map[string]int
}

// Executes a transaction if the rule and funds are valid
func ExecuteTransaction(tx Transaction, state *State) bool {
  if !tx.Rule(state) {
    fmt.Println("❌ Rule rejected the transaction.")
    return false
  }
  if state.Balances[tx.From] < tx.Amount {
    fmt.Println("❌ Insufficient balance.")
    return false
  }
  state.Balances[tx.From] -= tx.Amount
  state.Balances[tx.To] += tx.Amount
  fmt.Println("✅ Transaction executed successfully.")
  return true
}

func main() {
  // Initial blockchain state
  state := &State{
    Balances: map[string]int{
      "Alice": 100,
      "Bob":   50,
      "Carol": 0,
    },
  }

  fmt.Println("Initial balances:", state.Balances)

  // Simple rule: Only execute if Alice has at least 80 coins
  rule := func(state *State) bool {
    return state.Balances["Alice"] >= 80
  }

  tx := Transaction{
    From:   "Alice",
    To:     "Bob",
    Amount: 30,
    Rule:   rule,
  }

  // Execute the programmable transaction
  ExecuteTransaction(tx, state)
  fmt.Println("Balances after tx 1:", state.Balances)

  // Another rule: Only send money to Carol if Bob has more than 100
  rule2 := func(state *State) bool {
    return state.Balances["Bob"] > 100
  }

  tx2 := Transaction{
    From:   "Bob",
    To:     "Carol",
    Amount: 10,
    Rule:   rule2,
  }

  ExecuteTransaction(tx2, state)
  fmt.Println("Balances after tx 2:", state.Balances)
}

Even without Ethereum, we just created:

  • Conditional transactions
  • Verifiable, code-defined rules
  • A simple but powerful idea: money that moves when logic says so