I have recently been fortunate enough to give a presentation to two conferences, PyCon Australia and Kiwi Pycon, the Australian and New Zealand Python conferences, respectively. I'm not going to give a talk based around the presentation, as it's rather code heavy, and we know that doesn't translate well to an audio medium.

Instead, what I wanted to do, was to talk a little bit about the presentation pipeline that I used to prepare this talk. The input is a plain text file, edited in Emacs, using a mode called Org mode. The intermediate form is a LaTeX file, using the document class Beamer which is designed for presentations that are going to be projected. Beamer is apparently the German word for digital projector. The final output form is a plain PDF.

HPR isn't known for having many Emacs talks, so I should probably explain the idea of modes. Emacs has major modes and minor modes. For every document that you're editing there's one major mode, and any number of minor modes. So if I was editing a Python file for example, I would have the Python major mode which understands Python and can thus do Python specific things like Python code completion, and I would have a spell checker minor mode to check the spelling of comments, and another minor mode to automatically line wrap comment lines that are very long, and another minor mode to show what line number I'm currently editing, and another minor mode to blink the cursor and so on.

The other topic that I haven't heard too much on is LaTeX. LaTex is the venerable typesetting solution for Unix based systems. LaTeX documents have a single document class, and then any number of packages. In the case of my presentation, the document class is Beamer, which sets up all the margins and fonts to be good for presentations. Some of the packages I'm using are the symbols package, for arrows and maths symbols, and several graphics packages so I can draw trees in my slides.

I'm fairly comfortable with LaTeX, I could certainly write this presentation directly in LaTeX, but I think there are some advantages in using Org mode to generate my LaTeX instead.

As the name suggests, Org mode is designed to be an organisational mode, helping you write TODO lists and organise documents. While the document is just a plain text document that you can read and write with any text editor, the Emacs Org mode understands its own mark up and provides an outlining mode, where you can hide and expand trees of bullet points. The basic layout of a set of slides for a presentation is a tree of bullet points, where the top level bullet points are slides, and the second level of bullet points are lists of information put into each slide.

Another mark up that Org mode understands is that of code blocks, so that we can easily say ``this chunk of code is a Python block''. Org mode understands how to export this Python code block as a separate file, run it under Python, and can even insert the output of the program, or the result of a function, back into the original document as a code output block.

The advantage of having just one file for my presentation, versus one file for my presentation and a separate file for each code block, is that the code examples in my presentation never get out of sync with the code that I'm actually running. This style of programming where the documentation is the primary document, and the code files are generated, secondary documents, is the inverse of the typical way of programming where the code documents are the primary documents, and documentation, the secondary documents, are automatically generated.

This style of programming, where the primary document is documentation is called literate programming. The process of creating the documentation (the PDF in my case) is called weaving. The process of creating the code files is called tangling.

I really like having just one fi