HTML to Hiccup Conversion

Recently I wrote about alternative HTML syntaxes and in-language HTML DSLs like Hiccup. Those posts were about the broad issues. This one is about a boring and practical one.

Hardly any project consists entirely of fresh newly-written HTML. Most projects have snippets of HTML brought in from a (hopefully properly licensed) framework or template. For example, sometimes to start an application page I’ll use some HTML from a Bootstrap example page.

Such examples are written in ordinary HTML, not an alternative syntax or DSL, so I need a way to quickly and mechanically convert HTML to (in this example) Hiccup. A couple of years ago I wondered this, did some research, and put a few answers in the Hiccup repo wiki. It (still unchanged as of this writing) lists these tools capable of converting HTML to Hiccup:

Of those three, I found hiccup-bridge and this workflow quite easy to use:

  1. Add [hiccup-bridge “1.0.0-SNAPSHOT”] to project.clj
  2. Save example HTML snippets or pages in files
  3. lein repl
  4. (require ‘[hiccup-bridge.core :as hicv])
  5. (require ‘clojure.pprint)
  6. (clojure.pprint/pprint (hicv/html->hiccup (slurp “html_source/plain.html”)))
  7. Copy output or portions thereof to source code
  8. Repeat for additional files

Of course this could easily be wrapped in to a one-liner command line operation; but for maximum convenience someone should make an online tool for this conversion, analogous to Html2Jade. Maybe I’ll make such a thing, if no-one else does first.

Separation of Concerns != Separate Languages

A while back I wrote about the merits (and problems) of alternative HTML syntax such as Jade, HAML, etc. Another form of alternative syntax for HTML is an “internal DSL” in a programming language. There are various examples out there, including Domo for JavaScript and Hiccup for Clojure/CLJS.

Screen Shot 2014-10-03 at 10.16.20 PMScreen Shot 2014-10-03 at 10.17.29 PM

Hiccup syntax (which is to say, Clojure syntax) is of particular interest to me. Clojure spans server and web client code very well, and Hiccup data structures can be fed directly to Reagent for a concise and efficient dynamic web application based on React under the hood. Observe this snippet:

…in which ordinary Clojure “for” is used for iteration in a web page. I am experimenting with this tool stack – who knows what might emerge.

Why would anyone want to do this?

The reasons I have heard most often are:

  • Many projects are excessively polyglot without good reason. Even an “all JavaScript” project with a Node server typically has JavaScript, HTML, CSS, perhaps Sass, and various mini-languages (like CSS selectors) embedded inside.
  • Separation of Concerns does not have to mean separation of programming languages; even with separate programming languages, there are countless examples of poor separation of concerns, such as Java logic in a JSP template.
  • Your main programming already has a way to (for example) loop, yet you need a new and different way to loop at each layer.

The main reasons to stick with typical, different languages per layer/concern are more obvious:

  • Developers and non-developers probably already know how to use HTML and CSS; in particular, non-developer designers may have little interest in anything but HTML.
  • There are millions examples online for HTML and CSS.
  • Everyone else uses HTML and CSS as they are, let’s just do the same thing.

So again, why would anyone do this? The answer is as with other choices to use unusual technology – a chance to beat the averages and produce more value per time spent.