Modules and imports

A multi-file Fern program is one entry file that imports siblings. The entry file is whichever .fern you pass the compiler.

Imports

main.fern

import "./util";

function main(): i32 {
    return util.run();
}

util.fern

pub function run(): i32 {
    return 42;
}

The local name (util.run) is the path’s basename without the .fern extension. Re-aliasing isn’t supported yet.

Visibility

Top-level declarations default to private. Prefix with pub to export across modules:

pub function exported(): i32 { return 0; }
pub struct Public { x: i32 }
pub enum Status { Active, Inactive }
pub const CAP: i32 = 100;

function private_helper(): i32 { return 0; }  // module-local

Cross-module references to a non-pub declaration are rejected at load time with a diagnostic naming the offending qualifier.

Stdlib imports

The standard library lives at std/* — std/io, std/string, std/json, etc. Import the same way:

import "std/io";

function main(): i32 {
    io.println("hello");
    return 0;
}

The full list is under Standard library →.

Working with the language server

fern-lsp resolves imports across the workspace. With the VS Code extension installed:

• Hover over util.run() to see the imported function’s signature.
• Cmd/Ctrl-click jumps from the call site to util.fern.
• Rename a pub function and every cross-file caller updates.