Modules & Imports¶

MOL has a module system for organizing code across files.

Importing Files¶

Use the use statement to import from other .mol files:

-- Import everything from a file
use "./utils.mol"

-- Import specific names
use "./math_helpers.mol" : add, multiply

-- Import with a namespace alias
use "./config.mol" as Config
show Config.api_key

Exporting¶

By default, all top-level names in a file are exported. Use export for explicit control:

-- helpers.mol

-- Only these two will be importable
export greet, farewell

define greet(name)
  return "Hello, " + name
end

define farewell(name)
  return "Goodbye, " + name
end

-- This is private — not exported
define internal_helper()
  return "you can't import me"
end

Package Imports¶

Import built-in packages by name (without ./):

-- Import a built-in package
use "math"
use "collections"
use "text"

Available Packages¶

Package	Contents
`std`	Core utilities
`math`	Extended math & statistics
`text`	String processing
`collections`	Stack, Queue, LinkedList
`crypto`	Hashing, encoding
`random`	Random number generation
`rag`	RAG pipeline helpers

Package Manager¶

Initialize a Project¶

mol init

Creates a mol.pkg.json manifest:

{
  "name": "my-project",
  "version": "0.1.0",
  "main": "main.mol",
  "dependencies": {}
}

Install Packages¶

mol install math
mol install collections

List Installed¶

mol list

Search the Registry¶

mol search "vector"

Module Patterns¶

Config Module¶

-- config.mol
export api_url, max_retries, timeout

let api_url be "https://api.example.com"
let max_retries be 3
let timeout be 5000

-- main.mol
use "./config.mol" : api_url, timeout
show f"Connecting to {api_url} (timeout: {timeout}ms)"

Utility Library¶

-- string_utils.mol
export capitalize, slugify, truncate

define capitalize(text)
  let first be upper(slice(text, 0, 1))
  let rest be lower(slice(text, 1, len(text)))
  return first + rest
end

define slugify(text)
  return text |> lower |> replace(" ", "-")
end

define truncate(text, max_len)
  if len(text) <= max_len then
    return text
  end
  return slice(text, 0, max_len) + "..."
end

Struct Library¶

-- models.mol
export User, Post

struct User do
  name, email
end

struct Post do
  title, body, author
end

impl Post do
  define summary()
    return f"{self.title} by {self.author.name}"
  end
end

-- app.mol
use "./models.mol" : User, Post

let author be User("Alice", "alice@mol.dev")
let post be Post("Hello MOL", "First post!", author)
show post.summary()