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Introduction to Leo

Welcome to Leo, the programming language designed for building private applications on the Aleo blockchain.

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What is Leo?

Leo is an imperative, statically-typed programming language that abstracts low-level cryptographic concepts and makes it easy to integrate private applications into your stack. Leo compiles to circuits, making zero-knowledge proofs practical.
Leo provides a high-level language that makes zero-knowledge proofs accessible to developers without requiring deep cryptographic knowledge.

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Key Features

Developer-Friendly Syntax The syntax of Leo is influenced by traditional programming languages like JavaScript, Scala, and Rust, with a strong emphasis on readability and ease-of-use. Built for Privacy Leo compiles directly to Aleo instructions, enabling you to build applications with built-in privacy guarantees on the Aleo blockchain. Comprehensive Testing Tools Leo offers developers tools to sanity check circuits including:
  • Unit tests
  • Integration tests
  • Console functions for debugging
Type Safety As a statically-typed language, Leo catches errors at compile time, providing a safer development experience.

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The Aleo Ecosystem

Leo is one part of a greater ecosystem for building private applications on Aleo. The language works seamlessly with:
  • Aleo blockchain - The underlying Layer 1 blockchain that executes Leo programs
  • snarkVM - The virtual machine that runs Aleo instructions
  • snarkOS - The decentralized operating system for the Aleo network

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Example Leo Program

Here’s a simple Leo program that adds two numbers: 
program helloworld.aleo {
    // The 'helloworld' main function.
    fn main(public a: u32, b: u32) -> u32 {
        return a + b;
    }
}
Leo is currently in active development and the language is subject to updates and improvements. Check the GitHub repository for the latest changes.

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Use Cases

Leo is ideal for building:
  • Private DeFi applications - Create tokens, DEXs, and financial instruments with privacy guarantees
  • Private voting systems - Build governance mechanisms where votes remain confidential
  • Confidential gaming - Develop games with hidden state and fair outcomes
  • Private identity solutions - Create identity systems that preserve user privacy

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Version Information

The current version of Leo is 3.4.0. Leo requires Rust 1.93.1 or later.

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Next Steps

Install Leo

Get Leo installed on your system

Quick Start

Build your first Leo program

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License

Leo is open source software licensed under GNU General Public License v3.0.