Your first locus

Save the following as hello.ap:

locus Greeter {
    params { name: String = "world"; }
    birth() { println("hello, ", self.name); }
}

fn main() {
    Greeter { };
    Greeter { name: "Aperio" };
}

Run it interpreted:

aperio run hello.ap

You should see:

hello, world
hello, Aperio

What just happened

Greeter is a locus: a typed unit with a lifecycle. params declares its configurable state with defaults; birth() is the lifecycle method that runs when an instance is constructed.

Greeter { } constructs an instance using the default name; Greeter { name: "Aperio" } overrides it. Both instances run their birth() body to completion, then dissolve at the end of the surrounding statement.

That’s the smallest possible Aperio program: a locus with one field and one lifecycle method, instantiated twice at statement position. Every program is built out of compositions of this same primitive — locus declarations with params, lifecycle methods, and (as you’ll see next) bus interfaces and methods.

Next

Continue to A small program with shape to see two loci communicating across the typed bus. After that, the Concepts chapters walk through the structural model in depth.