Incunable

Incunable is a templating engine, which operates on Markdown/CommonMark documents and turns them into for example webpages. In the Markdown, you can use pre-defined templates, on which variable substitution will be performed.

The engine is made up of a series of awk scripts, along with some Bash and Python thrown in to manage the scripts.

The code is available at my GitHub account.

Template example

As an example, consider the template {{imgframe |file=bees.jpg |title=Bees entering their hive |ref=beeimage}}. Since the engine has a template called imgframe, it will be read and the content of the parameters will be inserted into the template. This is the content of the imgframe template:

<figure class="imageframe">
<img src="${file}" alt="${title}" />
<figcaption>Figure ${num}: ${title}</figcaption>
</figure>

We provided three parameters to the template: file, title and ref. In imgframe above there are three variables to substitute: file, title and num. The reason for the difference is that the original template that the user inputs is transformed during the pre-processing step of the engine.

Some templates have pre-processing scripts associated with them, and before performing the substitution, a pre-processing run will execute these scripts as needed. They do different things for different templates, and tend to have side-effects. The pre-processing script for imgframe will do a few different things:

It will adjust the file-parameter so that it is relative to the right path.
It will increment a counter for each imgframe that it encounters, and write this number associated with the ref parameter to a temporary file. This allows the ref template to later fetch this number and from the text refer to the figure.
It will insert the num variable into the imgframe reference.

In other words, for this template the pre-processing step will modify the file-parameter, insert a new parameter num, and it will write an association between the ref parameter and the num to a temporary file.

Pre-processing transformations

Some templates will as output write other templates; for example {{math |eq=\Delta}} will be turned into {{beginmath}}\Delta{{endmath}}, and this LaTeX-code will be made into an SVG and the template turned into {{img |file=eq_0.svg |title=\Delta}}. Thus, math produces beginmath and endmath, and beginmath produces img.

The engine takes care of creating a tree of the order in which the pre-processing scripts will be run, so that one can take over from another.

Algorithm

For each input file, the following operations will be performed:

The pre-processing scripts will be run, in the right order.
Template substitution is performed.
The document is turned into HTML with cmark-gfm (i.e. the GitHub fork of cmark).

Project name

Wikipedia says that "an incunable is a book, pamphlet, or broadside that was printed in the earliest stages of printing in Europe, up to the year 1500". In other words, a primitive form of automated printing. The likeliness is that this engine is a rudimentary template substitution engine, less performant and less versatile than more complex alternatives, but it is rather by design primitive.