Basic Reload

Each demo in this chapter is a sub-project with its own main.zolo and separate modules. To run it, open the directory in a terminal and run zolo dev:

cd examples/features/21-hot-reload/01-basic-reload
zolo dev main.zolo

The entry point imports two functions from the greeter module and enters an interactive read loop. The secret lies in how use greeter::{greet, farewell} is compiled: every call goes through a live-binding thunk that re-resolves the function in the module's export table — it never stores a fixed pointer.

Entry point: ENTER loop + import via live-binding.

main.zolo

Playground

// Feature: basic hot-reload
// Syntax: `zolo dev main.zolo` + edits to the `greeter` module.
// When to use: the "hello world" of `zolo dev` — edit-save-call flow.
//
// Press ENTER to call greet again. Edit greeter.zolo
// in the middle of the loop, save, press ENTER — you see the new code.

use greeter::{greet, farewell}

fn main() {
  greet("zolo dev")
  print("(edit greeter.zolo and save, ENTER to call again, 'q' to quit)")
  while true {
    let line = io::read("*l")
    if line is nil || line == "q" {
      break
    }
    greet("zolo dev")
  }
  farewell("zolo dev")
}

Requires the Zolo CLI/host — open in the playground or run locally.

The greeter module exposes both functions with pub fn. Edit the string inside greet, save, and press ENTER — the new text appears immediately. The identity of the export table is preserved (identity preserved), so any module that has already imported it remains valid automatically.

Edit the message while the program runs; the next ENTER uses the new version.

greeter.zolo

Playground

// Feature: basic hot-reload — simple module
// Syntax: `pub fn name(...)` in an imported file.
// When to use: edit the function and see the new version without restart.
//
// Edit the string below, save, and the next call from main.zolo
// prints the new version. The `LuaState` stays the same — only the
// `greet` function is swapped in the `greeter` module's exports table.

pub fn greet(name: str) {
  print("Hello, {name}! (edit this message and save)")
}

pub fn farewell(name: str) {
  print("Bye, {name}.")
}

Requires the Zolo CLI/host — open in the playground or run locally.

Challenge

While the program is running, add a third function pub fn shout(name) to greeter.zolo that prints in uppercase. Call it from main.zolo (just add shout to the use) and save both files in sequence. Observe the order of the reloaded: messages in the terminal.