In the development of a text-based multi-user dungeon (MUD) game, having a domain-specific language (DSL) that is both expressive and simple to use is key for writing game mechanics, commands, and logic. This paper explores the syntax and design of a custom language that supports variable creation, function definition and invocation, and commands necessary for a MUD game. The goal is to provide a language that is powerful enough to handle common game logic, while remaining easy to parse and integrate.

The language should support the following features:

1. Variable Declaration and Assignment: Ability to declare and assign values to variables.
2. Function Definition and Invocation: Support for defining reusable functions and calling them with arguments.
3. Built-in Commands: Special commands tailored for MUD actions (e.g., move, look, attack).
4. Control Flow: Conditional logic (e.g., if-else) to handle game state and logic.
5. Expressions and Operators: Arithmetic, relational, and logical operations for manipulating game data.
6. Basic Types: Primitive types such as integers, floats, strings, and booleans.
7. Comments and Readability: Support for comments to enhance code clarity.

The following syntax is designed to meet these requirements, drawing inspiration from modern scripting languages (e.g., Python, Lua) and classical languages for MUD development.

Variables are fundamental to store and manipulate data in any programming language. For this MUD language, we need a simple way to declare and assign variables.

let <variable> = <expression>

let health = 100
let name = "Hero"
let isAlive = true
let attackPower = strength * 2

Functions provide a way to encapsulate logic that can be reused throughout the game. Our language should support defining functions that can take parameters and return values.

def <function_name>(<param1>, <param2>, ...) -> <expression>

def add(a, b) -> a + b
def is_alive(health) -> health > 0
def attack(player, target) -> player.attackPower - target.defense

Since this language is specifically designed for MUDs, we need built-in commands that control player movement, interactions, and combat. These commands will interact directly with the game engine.

<command> <target>

move north
look at door
attack goblin
pick up sword

Control flow allows the game to make decisions based on conditions. We will use if-else statements to provide branching logic.

if <condition> then <expression> else <expression>

if health <= 0 then "You are dead" else "You are still alive"
if enemyHealth <= 0 then victory() else continueFight()

The language should support basic arithmetic, relational, and logical operators.

+   Addition
-   Subtraction
*   Multiplication
/   Division

==  Equal
!=  Not Equal
<   Less than
>   Greater than
<=  Less than or equal to
>=  Greater than or equal to

&&  Logical AND
||  Logical OR

let attackDamage = strength + weaponPower
let canOpen = key == "golden_key" && doorStatus == "locked"

The language should support common primitive types such as integers, floats, strings, and booleans. It can infer types during runtime.

• Integer: Whole numbers (1, 42, -10)
• Float: Decimal numbers (3.14, 0.99)
• String: Text enclosed in double quotes ("Hello World", "key")
• Boolean: Logical values (true, false)

Comments allow game developers to document their code, making it easier to read and maintain. We will support single-line comments using #.

# This is a comment

# Set the player's starting health
let health = 100

# Check if the player is alive
if health > 0 then "Alive" else "Dead"

Here's an example of how a game script might look using this proposed language syntax:

# Define the player's initial state
let health = 100
let strength = 15
let weaponPower = 5

# Define a function to calculate attack power
def attackPower() -> strength + weaponPower

# Define a function to check if the player is alive
def isAlive() -> health > 0

# Check player's health
if isAlive() then
    "You are ready for battle!"
else
    "You need to heal first."

# Move the player
move north

# Engage in combat
attack goblin

The language as proposed provides a strong foundation for MUD game development, but it can be expanded in the future with features like:

• Loops for repetitive actions (e.g., farming resources).
• User-defined data structures for complex game state management.
• Modules for organizing large scripts and separating game mechanics from content.

This proposed syntax offers a balance between simplicity and functionality, making it ideal for MUD game development. It provides all the essential features like variable assignment, function definition, control flow, and built-in commands tailored for game interactions. The language is designed to be easy to learn and use while offering enough power to handle complex game logic.