Working with multiple files

As a program grows, keep related types and functions in separate files. Create these three files and run commands from the directory containing app.xen:

project/
  app.xen
  shop/
    model.xen
    view.xen

app.xen:

module app;
import shop.model as model;
import shop.view as view;

fn main() {
    let item = model.Item { name: "tea", price: 3 };
    view.show(item);
}

shop/model.xen:

module shop.model;

struct Item { name: String, price: Int }

shop/view.xen:

module shop.view;
import shop.model as model;

fn show(item: model.Item) {
    println(item.name + ": " + int_to_str(item.price));
}

$ xen check app.xen
$ xen run app.xen
tea: 3

The same files are in the modules example directory. From the repository, run xen run examples/modules/app.xen.

Imports and names

import shop.model; loads shop/model.xen below the entry file’s directory. Each file declares a module matching its path. An entry file importing project modules also needs a declaration such as module app;. Mismatched names are errors.

as model provides a short name local to the importing file. Without an alias, use the full name shop.model.Item. Indirectly imported modules are not automatically available; import each module you use directly. Choose aliases that do not conflict with variables, types, or functions.

Standard library

Bring in the standard library with use std.string; or use std.string as text;. Use import for project files and use for bundled std.* and core.* modules. Do not place project files under the reserved names std or core. A single file using only standard-library modules does not need a module declaration.

Package manifests, visibility declarations, and module re-exports are unavailable. Avoid import cycles. Put shared types in a separate file both modules can import.