main and lib in the same crate

bar.rs

pub fn in_bar() {
    println!("bar");
}

Cargo.toml

[package]
name = "example"
version = "0.1.0"
authors = ["Joe Clay <27cupsofcoffee@gmail.com>"]
edition = "2018"

[dependencies]

foo.rs

use crate::bar::in_bar;

pub fn in_foo() {
    in_bar();
}

lib.rs

pub mod bar;
pub mod foo;

main.rs

use example::bar::in_bar;
use example::foo::in_foo;

fn main() {
    in_foo();
    in_bar();
}