Pattern matching

Vellum’s match statement branches on a value using literal patterns. It is a statement, not an expression.

Syntax

match scrutinee {
    pattern => body
    pat1 | pat2 => body
    else => body
}

Each arm’s body can be a block { ... }, a jump statement (return, break, continue), or a single expression statement.

Scrutinee types

The value you match on must be one of:

• Bool
• Int
• Float
• String

Patterns

Patterns are literals (including negative numbers such as -1) or identifiers that name a variable or property of a compatible type.

Use | to combine several patterns in one arm (or-patterns). An optional else => arm runs when nothing else matches.

import Debug

script GreetOnActivate : ObjectReference {

    event OnActivate(akActionRef: ObjectReference) {
        var actor = akActionRef as Actor
        if !actor {
            return
        }
        Notification($"Hello, {Greet(actor)}")
    }

    fun Greet(actor: Actor) -> String {
        match actor.GetEquippedItemType(1) {
            1 | 2 => return "blade user"
            7 => return "archer"
            else => return "adventurer"
        }
    }
}

Int and Float arms

If some arms use Int patterns and others use Float (or the scrutinee is the other numeric type), the compiler promotes as needed so comparisons stay consistent. Mixing Int and Float patterns in one match is allowed.

Control flow

match does not fall through between arms. Use return / break / continue inside an arm when you need to leave the enclosing function or loop.