All Unkept

You can’t compare language features, only languages

Posted in: Python, Software development, Haskell  — 

A lot of programming language debate is of the form “feature X is really good, every language needs it”, or “feature X is much better than its opposite feature Y”. The classic example is static vs dynamic typing, but there are many others, such as different types of meta-programming etc.

I often find myself pulled in both directions by these debates, as I’m rather partial to both Haskell and Python. But I’d like to suggest that doing this kind of comparison in the abstract, without talking about specific languages, is misguided, for the following reasons:

Language features can take extremely different forms in different languages

In my experience, static typing in Haskell is almost entirely unlike static typing in C, and different again from C# 1.0, and, from what I can tell, very different from static typing in C# 5.0. Does it really make sense to lump all these together?

Similarly, dynamic typing in Shell script, PHP, Python and Lisp are perhaps more different than they are alike. You can’t even put them on a spectrum — for example, Python is not simply a ‘tighter’ type system than PHP (in not treating strings as numbers etc.), because it also has features that allow far greater flexibility and power (such as dynamic subclassing due to first class classes).

Combination of features is what matters

One of my favourite features of Python, for example, is keyword arguments. They often increase the clarity of calling code, and give functions the ability to grow new features in a backwards compatible way. However, this feature only makes sense in combination with other features. If you had keyword arguments but without the **kwargs syntax for passing and receiving an unknown set of keyword arguments, it would make decorators extremely difficult.

If you are thinking of how great Python is, I don’t think it helps to talk about keyword arguments in general as a killer feature. It is keyword arguments in Python that work particularly well.

Comparing language features opens up lots of opportunities for bad arguments

For example:

Attacking the worst implementation

So, a dynamic typing advocate might say that static typing means lots of repetitive and verbose boilerplate to indicate types. That criticism might apply to Java, but it doesn’t apply to Haskell and many other modern languages, where type inference handles 95% of the times where you might need to specify types.

Defending the best implementation

The corollary to the above fallacy is that if you are only debating language features in the abstract, you can pick whichever implementation you want in order to refute a claim. Someone claims that dynamic typing makes IDE support for refactoring very difficult, and a dynamic typing advocate retorts that this isn’t the case with Smalltalk — ignoring the fact that they don’t use Smalltalk, they have never used Smalltalk, and their dynamically-typed language of choice does indeed present much greater or even insurmountable problems to automated refactoring.

Defending a hypothetical implementation

Defending the best implementation goes further when you actually defend one that doesn’t exist yet.

The mythical “smart enough compiler” is an example of this, and another would be dynamic typing advocates might talk about “improving” dynamic analysis.

Hypothetical implementations are always great for winning arguments, especially as they can combine all the best features of all the languages, without worrying about whether those features will actually fit together, and produce something that people would actually want to use. Sometimes a hybrid turns out like Hercules, and sometimes like the Africanized bee.

Ignoring everything else

In choosing a programming language, it’s not only the features of the language that you have to consider — there is long list of other factors, such as the maturity of the language, the community, the libraries, the documentation, the tooling, the availability (and quality) of programmers etc.

Sometimes the quality of these things are dominated by accidents of history (which language became popular and when), and sometimes they can be traced back to features of the language design.

Many language-war debates ignore all these things. But it’s even easier if you are not actually comparing real languages — just language features, abstracted from everything else.

I understand that comparing everything at once is difficult, and we will always attempt to break things down into smaller pieces for analysis. But I doubt that this goes very far with programming languages, because of the way the different features interact with each other, and also exert huge influence on the way that everything else develops e.g. libraries.


Language features exist within the context of a language and everything surrounding that language. It seems to me that attempts to analyse them outside that context simply lead to false generalisations.

Of course, being really concrete and talking about specific languages often ends up even more personal, which has its own pitfalls! Is there a good way forward?

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