What I like web templating languages for

December 7, 2015

In reaction to my entry on the problems with creating new (web) template languages, some of the people on Hacker News felt that the time of web templating languages was over due to various improvements in full programming languages. As it happens, I disagree. While there are situations where I would rather create HTML in code instead of through a template system, there are also plenty of situations where I would much rather use a template system.

In my opinion, templates work well in two interrelated situations. The first is when there is (much) more HTML than there is templating syntax to generate your dynamic content. One case this happens is if you're wrapping a form or some displayed (variable) information in a bunch of explanatory text. If you did this in the application's code, what you'd wind up with is mostly some large strings with periodic interruptions for the actual code; in my opinion, this is neither attractive nor very easy to follow (especially if the actual text of the page is broken up into multiple sections).

(I'd expect this to be even worse in a language that forced you to assemble the HTML through structured elements; you'd have a lot of code that existed just to make a whole stream of elements with the static content and string them together, interspersed with a few bits that generated the dynamic stuff.)

The second situation is where presenting the whole text and code of a page in one place makes it clearer what is going on and how the page is formed. Here, a single template is serving as the equivalent of a single giant function, except of course you probably wouldn't write a single giant function. Good template languages help this by creating compact but clear ways of describing their dynamic portions; generally these are much smaller than you could write in actual code without a lot of complex helper functions. While single templates can get tangled and complicated, this is in a sense a good thing because it's an honest expression of how complicated you're making generating the page be. Just as big, tangled functions are a code smell that suggests something needs to be refactored, big tangled template pages are probably a suggestion that they should be split into several template variants or otherwise restructured to be clearer.

Ultimately, templating languages versus programming languages are another incarnation of the gulf between shells and scripting languages. Programming languages are optimized for writing code that happens to have some embedded text, while templating languages are optimized for writing text that happens to have some embedded code. The more you have of one relative to the other, the more you will generally tilt one way.

(It's possible to make a templating system without embedded code, where your templates simply define places that code will later manipulate to add your custom content. I used to quite like this idea in the abstract, but I've come around to feeling that it's not what I want in practice.)

Written on 07 December 2015.
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Last modified: Mon Dec 7 23:12:13 2015
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