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yuzhe edited this page Mar 12, 2026 · 1 revision

FAQ

General

Q: What versions of Minecraft does RedScript support?

RedScript targets Minecraft 1.21.4+. The MC command validator uses the 1.21.4 command schema. Earlier versions may work but are untested.

Q: Does it support Bedrock Edition?

No. RedScript compiles to Java Edition datapacks (.mcfunction) and NBT structures. Bedrock's command syntax is different.

Q: Can I use RedScript with a modded server?

Yes, as long as the server supports vanilla datapacks. Paper, Purpur, and Fabric all work. Forge works if you have a datapack-compatible setup.

Language

Q: Why do all statements need semicolons?

The parser requires explicit statement terminators. This avoids ambiguity in complex expressions and keeps the grammar simple. (Yes, even scoreboard_set(...) needs a ;.)

Q: Can lambdas capture outer variables?

Read-only captures are allowed. Capturing a mutable outer variable is a compile error:

let base: int = 100;         // OK — read-only capture
let counter: int = 0;
let bad = () -> int {
    counter = counter + 1;   // ✗ Error: cannot capture mutable variable
    return counter;
};

Q: How does scoreboard work with temporary variables?

RedScript uses the rs objective (created in __load) for all compiler-generated temporaries ($t0, $t1, $const_N, etc.). These are global — there's no call stack. Each function call has isolated temp var names per call site (monomorphization), so sequential calls don't interfere.

Q: What's the difference between @tick and @tick(rate=20)?

  • @tick — function runs every server tick (20 times/sec at normal TPS)
  • @tick(rate=20) — function runs every 20 ticks (once per second)

Rate is implemented via a counter in the rs scoreboard.

Compilation

Q: What does __load do?

__load is auto-generated and registered in data/minecraft/tags/function/load.json. It runs when the datapack is (re)loaded and initializes the rs scoreboard and all $const_N values.

Q: Why use #fake_player names in scoreboard?

Fake players (names starting with #) are persistent scoreboard entries that don't correspond to real players. They're useful for global state that doesn't despawn when players leave.

Q: Can I mix RedScript with handwritten .mcfunction files?

Yes. RedScript generates files into data/<namespace>/function/. You can add your own functions to the same namespace by placing .mcfunction files there manually — they won't be touched by the compiler.

Optimizer

Q: How do I know if the optimizer is helping?

Run with --stats:

redscript compile game.rs --stats

Q: The optimizer changed behavior — what happened?

This is a bug. The optimizer should never change observable behavior. Please open an issue with a minimal repro.

Q: Can I disable specific optimizer passes?

Not individually yet. Use --no-optimize to disable all passes.

Testing

Q: Do I need a running MC server to use RedScript?

No. The unit tests and normal compilation don't require a server. The integration tests (mc-integration) require a Paper server with the testharness plugin — see Integration Testing.

Q: How do I run just the unit tests?

npm test
# or
npx jest --testPathIgnorePatterns=mc-integration

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