Level 33. Sharing Code Between Files

When your programs get bigger, you might want to put some functions in a separate file. That’s what imports are for!

Making things shareable

To share a function from a file, add pub in front of it:

// helpers.hc
pub fun double(x) => x * 2
pub fun triple(x) => x * 3
fun secret() => 42   // no pub — stays hidden!

pub is short for “public”. It means: “other files are allowed to use this.”

Importing

In another file, use import to bring those shared functions in:

// main.hc
import "helpers"

fun main() {
  println(double(5))   // 10
  println(triple(5))   // 15
  // secret() would fail — it's not pub!
}

The name in quotes is the file name without .hc. If helpers.hc is in the same folder as your main file, just write "helpers".

Picking what you want

Sometimes a file has lots of functions but you only need one. Use from ... import { } to pick:

from "helpers" import { double }

fun main() {
  println(double(5))   // works!
  // triple(5)         // nope — we didn't import it
}

Think of it like ordering from a menu: you don’t have to take everything, just pick the dishes you want.

Passing things along

If you want to share someone else’s functions through your file, use pub import:

// everything.hc
pub import "helpers"
pub import "math_tools"

Now anyone who imports everything gets all the pub functions from both helpers and math_tools. It’s like being a librarian: you collect books from different shelves and put them on one table.

🎯 Challenge: Create two files — animals.hc with pub fun cat() and pub fun dog(), and a main file that imports them and prints each animal’s sound!