Getting Started

This guide walks you through creating and running your first Lumen program.

Prerequisites

Make sure you have installed Lumen.

Create Your First Program

Create a file called hello.lm.md:

# My First Lumen Program

This is a simple hello world example.

```lumen
cell main() -> String
  return "Hello, World!"
end

## Run It

```bash
lumen run hello.lm.md

Output:

Hello, World!

What Just Happened?

1. Lumen extracted the code block from the markdown
2. It compiled the main cell
3. It executed the cell and printed the result

Adding Parameters

Let's make it more interesting:

cell greet(name: String) -> String
  return "Hello, {name}!"
end

cell main() -> String
  return greet("Lumen")
end

Output:

Hello, Lumen!

Running a Specific Cell

By default, lumen run executes the main cell. You can specify a different cell:

lumen run hello.lm.md --cell greet

Type Checking

Check your program without running it:

lumen check hello.lm.md

This validates types and catches errors early.

Using the REPL

For interactive experimentation:

lumen repl

lumen> let x = 42
lumen> x * 2
84
lumen> :help

REPL commands:

• :help — Show available commands
• :quit — Exit the REPL
• :load <file> — Load a file
• :type <expr> — Show the type of an expression

Next Steps

Now that you can run Lumen programs, continue with:

• Language Tour — Quick overview of all language features
• Tutorial: Basics — Learn core syntax
• Tutorial: Control Flow — Conditionals and loops
• Language Reference — Complete specification