HTML is Not a Programming Language?

This content originally appeared on CSS-Tricks and was authored by Alvaro Montoro

HTML is not a programming language.

I’ve heard that sentence so many times and it’s tiring. Normally, it is followed by something like, It doesn’t have logic, or, It is not Turing complete,.so… obviously it is not a programming language. Like it’s case-closed and should be the end of the conversation.

Should it be, though?

I want to look at typical arguments I hear used to belittle HTML and offer my own rebuttals to show how those claims are not completely correct.

My goal is not to prove that HTML is or is not a programming language, but to show that the three main arguments used for claiming it is not are flawed or incorrect, thus invalidating the conclusion from a logical point of view.

“HTML is a markup language, not a programming language”

This statement, by itself, sounds great… but it is wrong: markup languages can be programming languages. Not all of them are (most are not) but they can be. If we drew a Venn diagram of programming languages and markup languages, it would not be two separate circles, but two circles that slightly intersect:

A markup language that operates with variables, has control structures, loops, etc., would also be a programming language. They are not mutually exclusive concepts.

TeX and LaTeX are examples of markup languages that are also considered programming languages. It may not be practical to develop with them, but it is possible. And we can find examples online, like a BASIC interpreter or a Mars Rover controller (which won the Judges’ prize in the ICFP 2008 programming contest).

While some markup languages might be considered programming languages, I’m not saying that HTML is one of them. The point is that the original statement is wrong: markup languages can be programming languages. Therefore, saying that HTML is not a programming language because it is a markup language is based on a false statement, and whatever conclusion you arrive at from that premise will be categorically wrong.

“HTML doesn’t have logic”

This claim demands that we clarify what “logic” means because the definition might just surprise you.

As with Turing-completeness (which we’ll definitely get to), those who bring this argument to the table seem to misunderstand what it is exactly. I’ve asked people to tell me what they mean by “logic” and have gotten interesting answers back like:

Logic is a sensible reason or way of thinking.

That’s nice if what we’re looking for is a dictionary definition of logic. But we are talking about programming logic, not just logic as a general term. I’ve also received answers like:

Programming languages have variables, conditions, loops, etc. HTML is not a programming language because you can’t use variables or conditions. It has no logic.

This is fine (and definitely better than getting into true/false/AND/OR/etc.), but also incorrect. HTML does have variables — in the form of attributes — and there are control structures that can be used along with those variables/attributes to determine what is displayed.

But how do you control those variables? You need JavaScript!

Wrong again. There are some HTML elements that have internal control logic and don’t require JavaScript or CSS to work. And I’m not talking about things like <link> or <noscript> – which are rudimentary control structures and have been part of the standard for decades. I’m referring to elements that will respond to the user input and perform conditional actions depending on the current state of the element and the value of a variable. Take the <details>/<summary> tuple or the <dialog> element as examples: when a user clicks on them, they will close if the open attribute is present, and they will open if it is not. No JavaScript required.

So just saying alone that HTML isn’t a programming language because it lacks logic is misleading. We know that HTML is indeed capable of making decisions based on user input. HTML has logic, but it is inherently different from the logic of other languages that are designed to manipulate data. We’re going to need a stronger argument than that to prove that HTML isn’t a form of programming.

“HTML is not ‘Turing complete’”

OK, this is the one we see most often in this debate. It’s technically correct (the best kind of correct) to say HTML is not Turing complete, but it should spark a bigger debate than just using it as a case-closing statement.

I’m not going to get into the weeds on what it means to be Turing complete because there are plenty of resources on the topic. In fact, Lara Schenck summarizes it nicely in a post where she argues that CSS is Turning complete:

In the simplest terms, for a language or machine to be Turing complete, it means that it is capable of doing what a Turing machine could do: perform any calculation, a.k.a. universal computation. After all, programming was invented to do math although we do a lot more with it now, of course!

Because most modern programming languages are Turing complete, people use that as the definition of a programming language. But Turing-completeness is not that. It is a criterion to identify if a system (or its ruleset) can simulate a Turing machine. It can be used to classify programming languages; it doesn’t define them. It doesn’t even apply exclusively to programming languages. Take, for example, the game Minecraft (which meets that criterion) or the card game Magic: The Gathering (which also meets the criterion). Both are Turing complete but I doubt anyone would classify them as programming languages.

Turing-completeness is fashionable right now the same way that some in the past considered the difference between compiled vs. interpreted languages to be good criteria. Yes. We don’t have to make a big memory effort to remember when developers (mainly back-end) downplayed front-end programming (including JavaScript and PHP) as not “real programming.” You still hear it sometimes, although now faded, mumbled, and muttered.

The definition of what programming is (or is not) changes with time. I bet someone sorting through punched cards complained about how typing code in assembly was not real programming. There’s nothing universal or written in stone. There’s no actual definition.

Turing-completeness is a fair standard, I must say, but one that is biased and subjective — not in its form but in the way it is picked. Why is it that a language capable of generating a Turing Complete Machine gets riveted as a “programming language” while another capable of generating a Finite State Machine is not? It is subjective. It is an excuse like any other to differentiate between “real developers” (the ones making the claim) and those inferior to them.

To add insult to injury, it is obvious that many of the people parroting the “HTML is not Turing complete” mantra don’t even know or understand what Turing-completeness means. It is not an award or a seal of quality. It is not a badge of honor. It is just a way to categorize programming languages — to group them, not define them. A programming language could be Turing complete or not in the same way that it could be interpreted or compiled, imperative or declarative, procedural or object-oriented.

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So, is HTML a programming language?

If we can debase the main arguments claiming that HTML is not a programming language, does that actually mean that HTML is a programming language? No, it doesn’t. And so, the debate will live on until the HTML standard evolves or the “current definition” of programming language changes.

But as developers, we must be wary of this question as, in many cases, it is not used to spark a serious debate but to stir controversy while hiding ulterior motives: from getting easy Internet reactions, to dangerously diminishing the contribution of a group of people to the development ecosystem.

Or, as Ashley Kolodziej beautifully sums it up in her ode to HTML:

They say you’re not a real programming language like the others, that you’re just markup, and technically speaking, I suppose that’s right. Technically speaking, JavaScript and PHP are scripting languages. I remember when it wasn’t cool to know JavaScript, when it wasn’t a “real” language too. Sometimes, I feel like these distinctions are meaningless, like we built a vocabulary to hold you (and by extension, ourselves as developers) back. You, as a markup language, have your own unique value and strengths. Knowing how to work with you best is a true expertise, one that is too often overlooked.

Independent of the stance that we take on the “HTML is/isn’t a programming language” discussion, let’s celebrate it and not deny its importance: HTML is the backbone of the Internet. It’s a beautiful language with vast documentation and extensive syntax, yet so simple that it can be learned in an afternoon, and so complex that it takes years to master. Programming language or not, what really matters is that we have HTML in the first place.

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This content originally appeared on CSS-Tricks and was authored by Alvaro Montoro