What is Jumper?

Jumper is a scripting language for the JVM with the syntax of Java and the lightness of Lua. A Java application embeds it to run scripts written by other people - plugins and mods of a server, user automation, configs with logic - and decides exactly what those scripts may touch.

void onJoin(dyn player) {
    player.send("Welcome, " + player.name() + "!");
    server.broadcast(player.name() + " joined");
}

Why Jumper

• Familiar. Java syntax: if, for, classes, lambdas, import. Types are optional - dyn for dynamic values, int, String or a class where you want them checked.
• Light. Tables ({ x: 1 }), arrays, functions as values, closures, modules. No build step: a script is a text file.
• Uses Java directly. import java.util.HashMap;, new, method calls, fields - any class the host allows.
• Safe. Every script runs under an access policy (.jma): a whitelist of Java packages, classes and methods. Anything not listed is closed.
• Fast. An interpreter for code that runs once, a compiler to JVM bytecode for hot functions.
• Tooling. A language server and plugins for IntelliJ IDEA, VS Code and Neovim.

Files

File	What it is
.jmp	a script
.jma	an access policy: what scripts may use from Java
.jmc	a config: values and conditions, no loops and no Java