14 · Modules

mod creates a named namespace. Items inside a module are private by default — pub makes them accessible to callers. use brings items into scope without a full path. Modules map to files: a mod math; declaration in main.cssl loads math.cssl from the same directory.

// math.cssl — a module file
mod math {
    // Private helper — not accessible outside this module.
    fn two_pi() -> f32 { 6.28318 }

    pub fn circle_area(r: f32) -> f32 {
        3.14159 * r * r
    }

    pub fn circle_circumference(r: f32) -> f32 {
        two_pi() * r
    }

    // A sub-module.
    pub mod stats {
        pub fn mean(values: &[f32]) -> f32 {
            let sum: f32 = values.iter().sum();
            sum / values.len() as f32
        }
    }
}

// main.cssl
use math::{circle_area, circle_circumference};
use math::stats::mean;

fn main() !io {
    let r = 3.0_f32;
    println!("area          = {:.2}", circle_area(r));          // 28.27
    println!("circumference = {:.2}", circle_circumference(r)); // 18.85

    let data = [1.0_f32, 2.0, 3.0, 4.0, 5.0];
    println!("mean          = {:.1}", mean(&data));             // 3.0

    // Full path also works without use.
    println!("area again    = {:.2}", math::circle_area(2.0));  // 12.57
}

Output

area          = 28.27
circumference = 18.85
mean          = 3.0
area again    = 12.57

What the compiler sees

two_pi is invisible outside math — calling math::two_pi() from main.cssl is a compile error. use does not run any code; it is a compile-time name resolution directive. Circular use imports between modules are detected and rejected at compile time. The module tree mirrors the file system: mod math::stats lives in either math/stats.cssl or math.cssl as a nested mod stats { ... } block — both forms are equivalent.

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You’ve reached the end of Sigil by Example. Head to §B Language Reference for the full specification, or return to 01 · Hello World to review the basics.