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XIOMACS — hypermedia metaprogramming with org-babel

XIOMACS is a format-agnostic media creation and processing tool suitable for making games and other interactive applications.

XIOMACS is based on GNU Emacs. It delegates content processing to external applications like the GIMP, Pure Data, ImageMagick, FFMPEG, SBCL, and so on. XIOMACS uses Digital Asset Management (DAM) techniques to tag, annotate, store, and search a project’s various text and binary files (code, images, sounds) as well as metadata describing the files. Because XIOMACS knows what applications are available to edit and process data of various formats, the user can forget about organizing hundreds of files and instead launch their favorite editors from a hierarchical org-mode tree view of the assets. The use of plain text files for metadata enables simple grep-based searches.

With dataflow and literate programming concepts from org-babel, one can write Lisp programs that create or process assets automatically or semi-interactively. For example:

  • Generating thumbnails for images. Image-dired already does this.
  • Using ImageMagick to resample or otherwise process images
  • Using Ecasound to play back or record sound via ecasound.el
  • Converting an HD source video to lower definition and automatically updating the result when the original is changed
  • Converting Milkytracker XM to Ogg Vorbis automatically
  • Control JACKD from emacs
  • Live streaming

Asset metadata can conform to the Dublin Core metadata standard, and may also contain application-specific Lisp data meant for use by game engines. This metadata can be exported to a very simple text file format called PAK. PAK is trivially readable by both Common Lisp and Emacs Lisp, and simple reading/writing routines are included.

Because Emacs’ version control support is integrated with org-mode, you can version all the assets in a project from within Emacs.

;; Copyright (C) 2010  David O'Toole

;; Author: David O'Toole <>

;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with this program.  If not, see <>.


This work-in-progress article describes my approach to designing and developing games in Common Lisp, in a so-called literate style using GNU Emacs and Org Babel. My configurations and custom code are collected here in an org-mode essay containing executable Emacs Lisp code for a simple Digital Asset Management (DAM) system called “Xiomacs”. The name is short for ”hypermedia programming”.

Although this workbook is readable as a web page, it is best used interactively by opening it within GNU Emacs. Please download the raw version of this workbook,

The github page for this workbook is


In games development, especially solo or small-team scenarios, organizing assets becomes a significant problem. The “assets” of most programming projects are just code, and, if you’re lucky, some documentation. Each object of the programmer’s problem domain is associated with (probably) a chunk of code and a chunk of documentation.

The typical literate programming solution covers writing and transforming related chunks of documentation and code, but there is no general notion of asset management where related assets can be of different types: Lisp code, Emacs Lisp code, C code, PNG images, WAV sounds, OGG music, plain text, formatted text, and more.

In a video game, a game object (for example, an enemy spaceship) may be associated with any number of such resources. There will certainly be AI code (C, Lisp, etc), images, 3d models, textures, sounds, and so on. Creating, re-using, and re-mixing hundreds of game objects is hard when you have to maintain all these associations between files and code manually. So that when I want to edit “the image associated with that yellow alien over there”, I often have to hunt down the actual PNG files to edit, because the name of the PNG file never appears in the Lisp code—there’s a third file mapping resource names to files. The indirection makes the engine more flexible, but it’s another file to maintain.

My experiments with Xiomacs are an attempt to apply Orgmode organizational, publishing, and workflow tools to the problems of solo and small-group games development, with custom code and the unifying theme of literate programming.


Xiomacs is based on Orgmode and Org Babel, which are both GNU Emacs packages. Being familiar with these programs will help understanding the rest of this document.

Hypermedia programming with Xiomacs

There are a few new terms to worry about: workbook, entry, asset, attachment, and chunk.

Each “workbook” is just an org file—a collection of org entries describing collections of related assets and metadata. An asset is any relevant fragment of data, whether an external binary file (PNG, WAV) or data embedded in the entry itself (lisp, html, plaintext.) Each entry is given a unique UUID (Universally Unique Identifier) and the org entry with that UUID contains related asset data:

  1. Properties: for metadata. stored in the org properties drawer
  2. Attachments: to external asset chunks, with operations possible on those. This is based on org’s existing link/attachment functionality.

does this work with binary files?

  1. Chunks: of embedded asset text (lisp code, plain text, c code, etc) with org-babel

I use the term “workbook” because with Babel the workflow and project management features of Org are now integrated into the programming process. You can use org tags to categorize and search entries by category across multiple workbooks. You can use TODO and work logging, version control, and launch external editors like the Gimp and Audacity. Publishing support means you can share workbooks easily on the Web, and Babel’s noweb-style tangling means you can use true Literate Programming (in the classic Knuthian sense). Collaboration is possible with worg, and so on. And using org properties drawers to store metadata enables property search and processing via the org Properties API. Command-line media transcoding tools can be triggered by Babel, allowing further media workflow management.

Because different kinds of media are being linked/embedded into one document, and because Org Babel can actually use external programs to execute and process all kinds of program data and files and commands, this could be a step toward a kind of language-agnostic “hypermedia programming”.

There will also be support for managing asset libraries, and packaging workbooks into self-contained tarballs for Web collaboration and publishing.

These links provide some more background information:

Entries: the building blocks of workbooks

“Entry” is just a general term for an org heading and its content, which can of course contain any arrangement of further entries, each with its own properties and attachments.

See also info:org:Document Structure for more information on how Org files are organized.

Entries are assigned UUID’s (Universally Unique Identifiers) automatically when needed by org-mode.

tempo configuration and usage

(tempo-define-template "chunk"
  '(n "#+source: " (p "Chunk name: ") 
    n "#+begin_src " (p "Language: ")
    n "#+end_src ")

interactive function to create new entry

automatic ID upon creation

automatic metadata properties template


Chunks are the basic building blocks of hypermedia programs. Chunks can be of different media types, and may be stored either as an attached file (see “Attachments”, below), or inline (as text between “#+begin_src” and “#+end_src” tags, see also info:org:Literal examples.) Examples of file chunks are PNG, OGG, and OGV files. Inline data chunks may be in any text format, such as Common Lisp, HTML, or C++.

Each chunk has a unique UUID—the UUID of the entry containing the chunk.

The following data structure stores information about a chunk. This can be used for caching metadata and also for export. See “Data Interchange” below.

(defstruct chunk-info 
  name ;; Unique string name (or UUID) for the described chunk.
  properties ;; List of :keyword value pairs.
  file ;; Filename of file chunk, if any.
  data ;; A string with text data, if any (i.e. inline chunks.) 

Properties for metadata

Any ontology can be used to describe chunks via info:org:Properties and Columns. The Dublin Core metadata standard is a reasonable starting place, and defines these basic fields for use in describing and indexing resources of almost any kind:

(defvar xiomacs-properties-template "
"Text of org properties drawer entries to insert upon creating a new entry.")

(defun xiomacs-insert-properties-template ()
      (destructuring-bind (beg . end) 
          (org-get-property-block nil nil :force)
        (goto-char beg)
        (insert xiomacs-properties-template))))

For more information about Dublin Core, see these pages:

Application-specific metadata

Chunk properties may be used to embed control data for other applications. See “Resource data interchange” below.

** Operations on chunks *** Open in program

(describe-variable 'org-file-apps)

*** Process to create an output (wav->ogg)

* Attachments

Attachments are version-controlled external files associated with an entry. The entry’s properties data and other content are taken to describe the attachment. See also info:org:Attachments.

Orgmode will automatically commit changes to git-controlled attachments, if the current workbook’s org-attach-directory is also under git control.

Exporting workbooks as compressed binaries with all attachments

Interface enhancements

Consistent global key layout on F9-F12

Because viewing and browsing workbooks may involve various Org tree views and hidden source block bodies, there will be many hidden sections represented by an ellipsis at the end of the text line. Pressing TAB on most such lines will toggle display of the hidden text.

To make these hidden portions of text more obvious we can highlight chunks headers, and also the ellipses used to indicate hidden text.

(defface xiomacs-chunk-header-face '((t (:foreground "red" :bold t :weight bold))) "Face for chunk header lines.")
(defvar xiomacs-chunk-header-face 'xiomacs-chunk-header-face)
  (defvar xiomacs-chunk-regexp "^#\\+\\(source:\\|srcname:\\|function:\\)")
  (defun* xiomacs-fontify-chunk (limit)
    (while (re-search-forward xiomacs-chunk-regexp limit :noerror)
      (let ((beg (match-beginning 1))
            (end (match-end 1)))
        (add-text-properties beg end (list 'display (propertize (match-string 1) 'face xiomacs-chunk-header-face)
                                           'font-lock-fontified t)))))
(defface xiomacs-hidden-face '((t (:foreground "yellow" :underline "red"))) "Face for hidden xiomacs text.")
(defvar xiomacs-hidden-face 'xiomacs-hidden-face)
(defun xiomacs-fontify-blocks ()
    (goto-char (point-min))
    (while (re-search-forward "^#\\+begin_src[ ]+\\(\\(\\w\\|-\\)+\\)" nil t)
      (let* ((begin (point))
             (end nil)
             (language (match-string 1))
             (mode-command (intern (concat language "-mode")))
              (when (re-search-forward "^#\\+end_src" nil t)
                (forward-line -1)
                (setf end (point))
                (let ((string (buffer-substring-no-properties begin end)))
                    (insert string)
                    (funcall mode-command)
                    (buffer-substring (point-min) (point-max)))))))
        (when fontified-output
          (goto-char begin)
          (delete-region begin end)
          (insert fontified-output))))))

Mouse menus

(add-hook 'org-mode-hook
                    (lambda () (imenu-add-to-menubar "Imenu")))
(setf org-imenu-depth 5)

[#B] get mouse menus working for code blocks

(push (list "Source code chunks" "^#\\+\\(source:\\|srcname:\\|function:\\) \\(.*\\)$" 2)


You can use the following elisp chunks to activate the visibility enhancements—either interactively with C-c C-c, or by copying the code to your emacs initialization file.

(add-hook 'org-font-lock-hook #'xiomacs-fontify-chunk)
(remove-hook 'org-font-lock-hook #'xiomacs-fontify-chunk)
(setf org-ellipsis xiomacs-hidden-face)

Processes for creating and transforming chunks

How the Xiomacs source is made

Using Babel, the Emacs Lisp source code for Xiomacs itself is extracted from this workbook (or “tangled”, in literate programming terminology), to produce an output file called xiomacs.el.

There are also configuration chunks, snippets of elisp code you can execute in place (with C-c C-c) or copy to your emacs init file.

To make xiomacs.el from this workbook, execute the following elisp code chunk by placing point on it and pressing C-c C-c:


Assuming xiomacs.el is somewhere in your Emacs load-path, you can load it by executing this chunk:

(require 'xiomacs)

However, you can do a shortcut and use the following command to tangle the elisp code and load it into emacs in one step:

(org-babel-load-file (buffer-file-name))

Here is an overview of the output file’s organization.


The <<chunk-name>> tags above will be replaced by their corresponding definition chunks, defined elsewhere in this workbook, during the tangle process. Notice the “:tangle yes” argument; this is the only such block in this workbook. It means that in order to appear in the output file “xiomacs.el”, a chunk must be referenced somewhere in the expansion of this tangled chunk.

If you want the opposite behavior, use “#+property: tangle yes” as a control line in your org file, and “:tangle no” to turn it off for particular chunks.

Now we move on to some required libraries and other snippets needed in the final elisp file:

(require 'cl) 
(require 'ob-lisp)
(require 'tempo)
(provide 'xiomacs)

Recommended reading

The ideas, techniques, and terminology used in this paper have a variety of sources.

  • Donald Knuth, Literate Programming. This book is a reprinting of Knuth’s original papers on the subject.
  • Tim Evans, A meta-model for literate programming. This research paper generalizes literate programming practice by abstracting away the details of media type and processing behavior. In this model, “chunks” of content appear as nodes in an directed acyclic graph, with edges as relations between chunks. Attached to these edges are “processes” transforming chunks of one type into one or more other chunks or files.

    The resulting object model can be used to specify literate programming tools and actually generate them, and a simple example is given in Python.

    Emacs Lisp is ideal for this sort of work, and I believe I’ll benefit especially from Emacs Lisp’s portability, its excellent text processing tools, and its knack for gluing together diverse formats and programs.

    The meta model in Evans’ paper can be mapped more or less directly into org-mode’s features, and on top of this I’ve layered some more ideas and code. I’ve simplified some parts and elaborated on others, often re-using Emacs Lisp code from other projects of mine.


The last entry in a workbook is a good place to put odd pieces of text, TODO notes that aren’t part of the document, and any control data that needs to be at the end of the file (for example file-local Emacs variables; see info:emacs:Specifying File Variables.)

(htmlfontify-buffer nil "xiomacs-pretty.html")


[#B] org-file-apps

[#B] preview with inline-images / image-dired

[#C] org-icons

[#C] button toolbar? IDE? CEDET?

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