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Basics - Modules

Difficulty: 🟢 Beginner to 🟡 Intermediate
Time: 30 minutes

📚 What you’ll learn

Basic Imports

Standard Library

// Import specific function
import std::io::println;

int main() {
    println("Hello, World!");
    return 0;
}

Multiple Imports

// Import multiple symbols
import std::io::println;
import std::io::print;

int main() {
    print("Hello, ");
    println("World!");
    return 0;
}

Wildcard Imports

Import everything from a module using *.

// Import everything from std::io
import std::io::*;

int main() {
    println("All symbols available");
    return 0;
}

Relative Imports

// Import everything from local module 'utils'
import ./utils::*;

int main() {
    helper_function();  // Function from utils
    return 0;
}

Alias Imports

Rename modules or symbols to avoid conflicts or shorten names.

// Import std::io as io
import std::io as io;

int main() {
    io::println("Called via alias");
    return 0;
}

Selective Imports

Import specific symbols in a block.

// Import only println and print
import std::io::{println, print};

int main() {
    print("Selective ");
    println("Import");
    return 0;
}

Exporting

Use export to make functions or structs available to other modules.

Functions

// utils.cm
export int add(int a, int b) {
    return a + b;
}

// Private function (not exported)
int internal_helper() {
    return 42;
}

Structs

// models.cm
export struct Point {
    int x;
    int y;
}

export Point new_point(int x, int y) {
    return Point { x: x, y: y };
}

Re-exporting

// lib.cm
import ./utils;
import ./models;

// Re-export modules
export { utils, models };

Project Structure Example

my_project/
├── main.cm          # Entry point
├── utils/
│   ├── math.cm      # Math helpers
│   └── strings.cm   # String helpers
└── models/
    └── user.cm      # User struct

// main.cm
import ./utils/math::*;
import ./models/user::User;

int main() {
    int result = add(1, 2);
    User u = User { name: "Alice", age: 30 };
    return 0;
}

Circular Dependencies

Cm detects circular dependencies (A imports B, B imports A) and reports an error. Refactor common code into a third module to resolve this.

Common Mistakes

❌ Incorrect Path Syntax

// Wrong: Use :: for standard lib
// import std/io::println;

// Correct
import std::io::println;

❌ Using Unexported Symbols

// Error: internal_helper is not exported
import ./utils::internal_helper;

Next Steps

✅ Can organize code with modules
✅ Understand import/export syntax
⏭️ Next, explore the Type System

Previous: Pointers
Next: Type System —

Last Updated: 2026-02-08