Godot scripting via s7 Scheme

Godot integration for the wonderful s7 Scheme. s7 interpreters can be added to scenes as Scheme nodes which can load and evaluate code.

The Scheme code has access to the Godot API via a simple interface (syntax is still in flux):

• the Scheme Godot node, which serves as an entry point into the scene model, is exposed as the *node* constant
• Godot nodes can be accessed through their relative path to *node* via the $ macro, e.g. ($ Sprite2D)
• properties can be read via applicable object syntax, e.g., (*node* 'owner) reads the owner property of the enclosing node
• applicable syntax can also read nested properties, e.g., (*node* 'owner 'name) reads the name of the owner of the enclosing node
• applicable syntax can call methods, e.g., (*node* 'owner '(get_child 0) 'name), even when the arguments are not constants, (*node* `(get_child ,child_index))
• although explicit syntax for method calls is also provided for when it makes things clearer, (! (*node* 'owner) 'get_child 0)
• properties can be set via generalized set! syntax, e.g., (set! (*node* 'owner '(get_child 0) 'name) "Deeply Nested set!")
• Scheme code can connect to signals via connect!

A more complete example of the available syntax:

(begin
  ;; Godot objects are exposed as applicable objects.
  (define button (*node* 'owner '(get_child 1)))

  (define (button-append! suffix)
    (let ((text (button 'text)))
      ;; Godot properties are set via generalized set! syntax
      ;; and there are two main ways of calling Godot methods:
      ;;  * (! <obj> <method symbol> &<args>)
      ;;  * (<obj> '(<method symbol> &<args>))
      ;; ! is preferred for effectful calls such as
      ;; 'insert below, and, in general is more amenable
      ;; to optimisations. Applicable object syntax
      ;; is convenient for const methods like '(length) below and
      ;; `(get_child 1) above.
      (set! (button 'text)
        (! text 'insert (text '(length)) suffix))))

  (define (function-handler)
    (button-append! "!"))

  (define (symbol-handler)
    (button-append! "'"))

  ;; Signals can be connected to symbols, lambdas and arbitrary procedures.
  ;; Symbols provide late binding, i.e., the ability to redefine the
  ;; procedure bound to a symbol / signal via the repl while the program is
  ;; running.
  (connect! button 'pressed 'symbol-handler)
  (connect! button 'pressed (lambda () (button-append! "λ")))
  (connect! button 'pressed function-handler))

Status

Very experimental but a lot of fun to play with. Use it at your own risk.

Building

Make sure to update all git submodules:

    git submodule update --init

Build and launch the demo project with make run or more explicitly via:

    scons && godot -e --path demo

Build the Android target with make android or more explicitly via:

  scons platform=android target=template_debug

Make sure ANDROID_HOME is set.

Emacs live editing support (WIP)

Install Geiser then add the following to your Emacs configuration:

(add-to-list 'load-path "~/path/to/godot-s7-scheme/emacs/")
(load "geiser-godot-s7-autoloads.el")

The Emacs extension automatically recognize Scheme files inside Godot project directories as Godot s7 Scheme files.

Connecting to the editor

1. Start Godot with --s7-tcp-port=<port-number> (and/or --s7-tcp-address=<bind-address>).
2. Check the port number in the console.
3. In Emacs, M-x connect-to-godot-s7 3.1 You can also open a Scheme repl from the shell with nc <bind-address> <port-number>

Connecting to a running scene

1. In Godot, select Debug / Customize Run Instances... / Main Run Args
   • Add --s7-tcp-port=<port-number> and/or --s7-tcp-address=<bind-address>.
2. Steps 2 and 3 as above.

Roadmap

• use Godot API from Scheme
• live coding interface via Emacs
• expose tree-sitter API to Scheme
• Scheme editor with syntax highlighting
• Scheme notebooks
• expose Godot signals from Scheme
• subclass Godot classes from Scheme
• register Scheme as a proper script language extension