ReDScribe Tutorial

What is ReDScribe?

ReDScribe is a GDExtension plugin that runs Ruby (mruby) inside Godot for writing DSL.

Features:

• 💎 You can execute mruby code (a lightweight Ruby) in Godot and emit signals from mruby to Godot.
• ✏️ You can write and edit Ruby files in the Godot Editor.
• ⬛ You can try out Ruby interactively in Godot.

What is Godot?

Godot is a cross-platform game engine released under the MIT license.

GDScript

GDScript is Godot's built-in scripting language.

extends Node
class_name MyNode

const Foo = 'CONST'
var bar := [1, 2, 3]

func _ready() -> void:
    do_something()

func do_something() -> void:
    # ...
    return true

extends Resource
class_name MyResource

@export var foo : String
var bar : int

func do_something() -> bool:
    # ...
    return true

Signal

Signals are used to send messages from one game object to another.

# When the Button node's pressed signal is emitted
func _on_button_pressed() -> void:
    do_something()

# A custome signal
signal some_signal(val: String)

func _ready() -> void:
    some_signal.connect(_on_some_signal)

func do_something() -> void:
    # ...
    some_signal.emit('foo')

func _on_some_signal(val: String) -> void:
    print_debug(val) # output 'foo'

ReDScribe is using signals to bridge between Ruby (mruby) and Godot.

What is Ruby?

Ruby is an object-oriented programming language that has an elegant syntax.

class Game
  attr_accessor :score

  def initialize
    self.score = 0
  end

  def roll(pins)
    # ...
  end
end

game = Game.new
20.times { game.roll(1) }

Ruby favors developer freedom over rigid rules.

• Optional return
• Optional ;
• Optional ()
• Method names can end with ! or ?
• Everything is an Object
• Even built-in class methods can be redefined
• Metaprogramming

module IntegerExt
  def days_ago
    Date.today - self
  end

  def !
    (1..self).reduce(1){|sum, i| sum *= i }
  end

  def to_kanji
    chars = %w(〇 一 二 三 四 五 六 七 八 九)
    to_s.split('').map{|i| chars[i.to_i] }.join
  end

  def method_missing(name, *args)
    "#{to_kanji}#{name}#{args.map(&:to_s).join}"
  end
end
Integer.prepend IntegerExt

Date.today # => 2025/7/15
4.days_ago # => 2025/7/11

5.!        # => 120

2025.年 7.月 # => '二〇二五年七月'

mruby

mruby is a lightweight implementation of the Ruby language designed for embedding into applications.

ReDScribe runs mruby inside Godot using GDExtension.

What is DSL?

A domain-specific language (DSL) is a programming language or structured text format designed with the vocabulary of a particular domain in mind, with minimal syntactic noise.

Ruby is often used for internal DSLs because its syntax is less noisy.

player.rb

class Player
  def initialize(name)
    @name = name
  end

  def walk
    puts "#{@name} walk"
  end

  def jump
    puts "#{@name} jump"
  end
end

def player(name, &block)
  Player.new(name).instance_exec(&block)
end

require 'player'

player 'Alice' do
  3.times { walk }
  jump
end

# => Alice walk
#    Alice walk
#    Alice walk
#    Alice jump

This tutorial will guide you through using ReDScribe to build your own domain-specific languages in Ruby, making game programming feel more expressive, personal, and fun.