Language ReferenceHeader Modes

Header Modes

JOEL uses file headers to determine execution mode and target platform.

Execution Modes

Interpreted Mode

[Interpreted]

# Fast development, dynamic types
let x = 10
let name = "JOEL"

Characteristics:

  • Fast development cycle
  • Dynamic type checking
  • Hot-reload support (coming soon)
  • Great for prototyping and AI/ML

Compiled Mode

[Compiled]

# High performance, static types
let x: i32 = 10
let name: str = "JOEL"

Characteristics:

  • Static type checking
  • Zero-cost abstractions
  • Optimized performance
  • Production-ready code

Target Platforms

Specify the target platform with [target ...]:

Native

[Compiled]
[target native]

# Compiles to native binary (x86_64, ARM64)

WebAssembly

[Compiled]
[target wasm32]

# Compiles to WebAssembly for web/mobile

Ethereum (EVM)

[Compiled]
[target evm]

contract Vault {
  # Smart contract code
}

Solana

[Compiled]
[target wasm-solana]

contract Counter {
  # Solana program
}

Examples

Development Script

[Interpreted]

# Quick script for development
fn main() {
  print("Development mode")
}

Production Binary

[Compiled]
[target native]

# Production application
fn main() {
  # Optimized code
}

Smart Contract

[Compiled]
[target evm]

contract Token {
  state let total_supply: uint256
}

Web Application

[Compiled]
[target wasm32]

component App() {
  # UI component
}

Mode Selection Guide

Use [Interpreted] when:

  • Prototyping
  • AI/ML development
  • Quick scripts
  • Learning JOEL
  • Workflows

Use [Compiled] when:

  • Production systems
  • Performance-critical code
  • Smart contracts
  • Native applications
  • Deploying to production

Next Steps

Syntax OverviewData Types