Translating mcfunction to Kotlin

Most .mcfunction files are written as a sequence of commands. Kotlin can still do that, but the real benefit is that you can name values, branch normally, loop normally, and split behavior into reusable functions.

Command Chain to Function

Datapack:

scoreboard players set test myscore 1
tellraw @a {"text":"Score set!"}

Katton:

import top.katton.api.ServerPhase
import top.katton.api.ServerScriptEntrypoint
import top.katton.api.dpcaller.getOrCreateObjective
import top.katton.api.dpcaller.setScore

@ServerScriptEntrypoint(ServerPhase.READY)
fun scoreboardExampleMain() {
    // Get or create the scoreboard objective.
    val obj = getOrCreateObjective("myscore")
    // Set the score of "test" to 100.
    setScore("test", obj, 100)
}

The important shift is not the syntax. It is that main() can now call any Kotlin code you write.

Conditions

Datapack conditions often become execute if ... run function .... In Kotlin, use if.

fun rewardIfReady(score: Int) {
    if (score >= 10) {
        println("Reward unlocked")
    }
}

For game-state checks, read the entity, scoreboard, NBT, or event argument first, then branch on normal values.

Loops

Datapack loops usually need recursive schedule function calls or repeated command blocks. In Kotlin, loop over collections directly.

fun announceNames(names: List<String>) {
    for (name in names) {
        println("Loaded player $name")
    }
}

When looping over entities, first build a selector or use an event argument, then work with the returned objects. See Selectors and Entity Access.

Reusable Logic

Instead of copying the same command block into many functions, extract a Kotlin function:

fun clampWave(value: Int): Int {
    return value.coerceIn(1, 10)
}

Use small functions for rules, calculations, and formatting. Keep command-like calls at the edges where they actually affect the world.

A Practical Rule

If a line exists only to simulate programming, translate it into Kotlin. If a line is already a direct Minecraft operation, call a Katton helper or keep the original datapack function for now.