Custom Effects

Sounio lets you declare your own effects to model domain-specific side effects.

Declaring an Effect

An effect is a named set of operations:

effect Fail {
    fn fail(msg: string) -> !
}

Using an Effect

Call effect operations like normal functions, and declare the effect in the signature:

fn might_fail() with Fail {
    Fail.fail("something went wrong")
}

Propagating Requirements

Callers must also declare the effect:

fn main() with Fail {
    might_fail()
}

If you forget, the compiler reports an error:

fn main() {
    might_fail()  // ERROR: Fail effect not declared / handled
}

Spec Note: Effect Handlers

The language design includes algebraic effect handlers (resumption, interpretation, etc.). If you see handle / resume syntax in older docs, treat it as spec-level unless the current compiler mode explicitly supports it.

Next

• IO
• Effects Overview