Reify is a lightweight templating engine built on regular expressions intended for finding and replacing complicated patterns in documents. The original intended use-case for Reify is for mass-editing repetitive, bad/messy HTML and XML markup, usually that generated by a computer, but it will work in any document.

There are two slightly different variants of Reify: one for patterns that are to be searched for in a document and one for patterns that are supposed to replace the original one. For the sake of simplicity, the former shall be called the "input template" and the latter will be the "output template"

A "slot" is a placeholder for some data. In an input template, a slot represents some data in the original document; in an output document, it represents a place where data from the original document should be put. All slots consist of some text in double braces: {{...}}. The main difference between an input template and an output template is the kinds of slots each of them can use.

The first kind of slot is a wildcard slot, which is just {{}}. It can only appear in an input template and it represents data in the document that might be used when during the reformatting. These are automatically numbered in the order they appear and they can be referenced by number in the output template. Say you are trying to render an item in an RSS feed as an anchor tag in HTML. You may do it like:

<!-- INPUT -->
<item>
    <title>{{}}</title>
    <link>{{}}</link>
    <description>{{}}</description>
</item>

<!-- OUTPUT -->
<a href="{{2}}" title="{{3}}">{{1}}</a>

For your own sanity, if you choose to go this route, you may want to write the numbers in the input template slots. This won't affect the way Reify actually numbers the slots, but it saves a bit of headache.

Still, a numbering scheme can get difficult and inconvenient. This is why you are also allowed to use labels. A label can contain letters, numbers, hyphens, or underscores. The number reminders you can write in the slots are also labels. Labelled slots can still be referenced by number.

Updating the RSS example above to use labels:

<!-- INPUT -->
<item>
    <title>{{title}}</title>
    <link>{{link}}</link>
    <description>{{desc}}</description>
</item>

<!-- OUTPUT -->
<a href="{{link}}" title="{{desc}}">{{title}}</a>

If there's any information you don't plan on using, but that doesn't fit an easy pattern (such as a UUID string or a hash or a randomly generated string), you can use a null slot, {{:}}, to say "there is some data here, but it isn't important". It's equivalent to (?:.*) in regex. Of course, a null slot can only be placed in an input template.

In the output template, there are a few shorthands you can use to place slot data consecutively. You can place multiple labels or numbers into the same slot as a space-separated list. This is good if, for example, you have HTML with a lot of useless <span> elements.

<!-- INPUT -->
<div>
    <span class="author">{{author}}</span>
    <span class="title">{{title}}</span>
    <span class="year">{{year}}</span>
</div>

<!-- OUTPUT -->
<div class="citation">{{author title year}}</div>

If you are using numbers, you can even use ranges:

<!-- OUTPUT -->
<div class="citation">{{1..3}}</div>

Note that ranges are inclusive of both bounds.

Cheat Sheet

The Reify command line tool, reify, allows you to compile regular expressions from Reify templates, find patterns in a file matching a template, and perform find-and-replace on whole documents. These three functions correspond to three commands: generate, find, and subs, respectively.

Perhaps the most useful command is reify subs. This is a powerful find-and-replace tool that will search in a document for patterns matching an input template and replaces them with the output template. By default it just prints out the reformatted document, but it can be redirected to another file or the substitution can be done in-place. It takes the following arguments:

• -it or --input-template: Path to the template you want to replace
• -ot or --output-template: Path to the template you want to replace the old pattern with
• -f or --file: Path to the file you want to perform find-and-replace on

And it can take the following flags:

• -W or --conserve-whitespace: Normally when input templates are compiled, all newlines or series of whitespace characters are replaced with \s*, since whitespacing in, for example, machine-generated markup can often be all over the place, so you can write clean markup in the input template and it will match any messy markup in the document. Setting this flag will force all whitespace in the input template to be taken literally.
• -I or --in-place: Performs the substitution in-place, meaning that the original document will be edited to have all occurrences of the input template replaced with the output template.

The command reify generate allows you to compile Reify templates into regular expression syntax. This can help if you want to use your own find-and-replace tool, or if you just need to generate a complicated regex for a program. It takes the following arguments:

• -it or --input-template: Path to input template
• -ot or --output-template: Path to output template

It can also take the following flags:

• -W or --conserve-whitespace: Does the same thing it does for subs

reify find will take an input template and find all occurrences of that template in a file. All matches will be printed out in the terminal with the data from the slots highlighted in green. This is useful for testing templates. It takes the following arguments:

• -t or --template: Path to the template you want to search against
• -f or --file: Path to the file you want to search in

And it can take the following flags:

• -W or --conserve-whitespace: Does the same thing it does for subs and generate

reify subs -I -it path/to/input/template -ot path/to/output/template -f path/to/file

You will be prompted for any arguments you forget, so you could say reify subs -I and you will be prompted for the input template, output template, and file.

reify find -t path/to/input/template -f path/to/file

This will print all the text in the document that matches the pattern in the input template. Any data in slots will be highlighted in green. As with the last one, you'll be prompted for the template and file if you don't provide them.

The Reify GUI allows for interactive editing, checking, and substitution of text in a document. More details to come as I build it out.

1. Add a graphical user interface.
2. Create a proper API so it can be more readily employed in other applications.
3. Maybe make the parsing algorithm a bit more sophisticated
4. Make it more fully-featured. Currently it applies to only a few narrow use-cases and can't do nearly as much as regex can.

Copyright © 2019 Aidan T. Manning

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