Spells

Functions in Rune are called spells and are declared and invoked using a simple, readable syntax.

Defining a Spell

Spells are defined using the spell keyword, followed by the spell name, a parenthesized parameter list, and a block statement enclosed in braces {}:

spell greet(name) {
    write("Greetings,", name)
}

Parameters

Parameters inside the parentheses can be space-separated or comma-separated. Both forms are valid:

# Space-separated parameters (idiomatic):
spell add(a b) {
    return a + b
}

# Comma-separated parameters:
spell add(a, b) {
    return a + b
}

Invoking a Spell

You can invoke (call) a spell in two ways:

1. Direct Call — Standard call syntax common in most languages.
2. Explicit Cast Call — Prefixed with the cast keyword. Both forms are identical.

# Direct call:
greet("explorer")

# Explicit cast call:
cast greet("explorer")

Return Values

Use the return keyword to exit a spell early and return a value:

spell max(a, b) {
    if a > b {
        return a
    }
    return b
}

If a spell completes execution without hitting a return statement, it implicitly returns empty.