WIP Check remaining todos or code samples

rAthena script language interpreter

A grammar, parser, compiler and VM implementation for rAthena script language.

Inspired by https://github.com/Doddler/Scripting-Language-Guide and https://craftinginterpreters.com/.

VM architecture inspired by jvm

This crate offers a compiler and VM to be embedded in game server.

Generate Parser

java -jar bin/antlr4.9.4-rust.jar RathenaScriptLang.g4 -Dlanguage=Rust -visitor -o src/parser

Grammar

Grammar is defined in RathenaScriptLang.g4 file. Parser is generated using antlr.

Integration with a server

Currently only integretation for a rust server implementation is targeted. A C/C++ API can be provided to integrate it in herculesWS and rathena

Vm should be run inside mmo server. NPC script can be pre-compiled or compiled at VM startup, using this crate.

Rathena script command related to game, almost all commands listed here, have to be implemented in server side.

Compiler considers those command as "native" functions. VM require to implement a native functions handler, which has to be implemented by the server.

Example of integration

Features

In addition of providing a compiler and vm to interpret rathena script lang, this implementation provides:

• Nice compilation errors for easier code writing

Variable ".@c" is declared as a Number but is assigned with a String.
test_script 12:4.
l12	    .@c = str();
	    ^^^

• Nice runtime errors for easier debugging

Can't call getarg(1) which is greater than number of arguments provided: 1. Maximum index is 0. Consider calling getarg with a default value: getarg(1, DEFAULT_VALUE)
test_script 5:15.
l5	        .@a$ = getarg(1) + " world";
	               ^^^^^^^^^

0: _main
	at /home/ragnarok/dev/npc/warps.txt(Warper:3)
1: my_func
	at /home/ragnarok/dev/npc/warps.txt(Warper:5)

• AOT Compilation for faster server startup
• AOT Compilation type checking for variable assignment
• AOT Compilation argument count checking for native functions

Server implementation notes

Server should implement natives functions (commands starting after point 2) in order to make scripts working.

In addition of native functions listed in link above, server should implement some extra native functions, for example to support char, account and server variable scopes.

more details here

Limitation and workaround

Lack of reference/value consistency in the language

Some methods return reference or value dependending on the context, forcing to implement some "hack" to support all use case.

Here an example with getelementofarray but there are plenty of example

.@a$[0] = "hello"; // This is a valid array of string declaration

getelementofarray(.@a$, 0) + " world";      // getelementofarray() returns a value
setarray getelementofarray(.@a$, 0), "bye"; // getelementofarray() returns a reference so we can assign "bye" to array element 0

Global variable array

• getglobalarrayref: put reference of a global variable array on the stack

Architecture

Language specificity

Althought Rathena script lang is not an oriented object programming language, it has notion of:

• Global script(or npc) state, which are alive while server is alive
• Global script(or npc) state, which are alive for the duration of the script execution

To ease the implementation of the VM we will call:

• Script/NPC -> Class
• Script/NPC instance -> Instance

VM Memory layout

flowchart LR
    subgraph S1[<b>VM</b>]
        direction TB
        A1["ConstantPool<hr><ul><li><i>String (#quot;hello world#quot;)</i></li><li><i>Number(1)</i></li></ul>"]
        A2[NativeMethodPool<hr><ul><li><i>print</i></li><li><i>callfunc</i></li><li>...</li></ul>]
        A3[Heap<hr><ul><li><i>Arrays</i></li><li><i>Instances</i></li></ul>]
        A4[ClassPool<hr><i>Classes</i>]
        A5[InstancePool*<hr><i>Instances</i>]
        A3 --> A1
        A3 --> A5
    end

    subgraph S3[<b>Callframe</b>]
        direction TB
        C1[Operand Stack]
        C2["Local variable pool<hr><ul><li><i>String pointer</i></li><li><i>Number pointer</i></li></ul>"]
        C2 --> A1
    end

    subgraph S2[<b>Thread</b>]
        direction TB
        B1[Stack<hr><ul><li><i>References</i></li></ul>]
        B1 --> A1
        B1 --> A2
        B1 --> A3
        B1 --> C2
    end

Loading

VM lifecycle

graph TD
  Server[RagnarokServer] --> Boot --> Load[Load bytecode] --> VM;
    Compiler --> ReadTxt[Parse source] --> AST[Generate AST] --> Visit[Visit ast nodes] --> Chunk[Generate chunks] --> ByteCode[Write bytes code] --> Bytecode;
    VM[VM] --> Startup;
    Server --> Player[Player interact with NPC] --> Execute;
    Execute[Execute script] --> VM[VM] --> Instantiate[Instantiate script] --> Read2[Read byte code] --> Run[Execute program] --> I2[Execute op code];
    Startup[Bootstrap] --> Loading --> Linking --> Initialization
 

Loading

Garbage collection (design in progress)

All "data" pool store references to constant pool. Only constant pool store values.

TBD