How-To: Model Complex Domain Logic

How-To: Model Complex Domain Logic

Learn how to use Vox’s expressive type system to model your application’s domain logic effectively.

1. Algebraic Data Types (ADTs)

Vox supports powerful ADTs (sum types) for representing state that can be one of several variants.

type OrderStatus =
    | Pending
    | Processing(staff_id: str)
    | Shipped(tracking_number: str)
    | Delivered(timestamp: int)

2. Pattern Matching

Use the match expression to handle ADT variants with full type safety.

fn describe_status(status: OrderStatus) to str {
    return match status {
        Pending         => "Waiting for staff"
        Processing(id)  => "Being handled by " + id
        Shipped(track)  => "In transit: " + track
        Delivered(ts)   => "Package reached destination"
    }
}

3. Composing Structs

Group related data into named structs.

type Address {
    street: str
    city:   str
    zip:    int
}

type Customer {
    name:  str
    email: str
    shipping_address: Address
}

4. Validation with @require

Add runtime guards to your data types using the @require decorator.

// vox:skip -- illustrative future syntax; @require only decorates fn today, not type
@require(len(self.password) > 8)
type UserAccount {
    username: str
    password: str
}

Summary

• Describe mutually exclusive states and data variants cleanly using ADTs (Sum Types).
• Avoid invalid states with constructor validation guards via @require.
• Pattern match to strictly process all possibilities at compile time.

Related

• Language Syntax — Full type system syntax.
• Database Schema — Modeling domain with tables.