What do you mean by the expressiveness of a programming language?

Question

I see a lot of the word \'expressiveness\' when people want to stress one language is better than the other. But I don\'t see exactly what they mean by it.

• Is it

Answer 1

Precision, concision, and readability are the primary components in expressiveness.

Answer 2

Personally, I feel that the "expressiveness" of a language really comes down to how clearly the language constructs can "express" the developer's intentions.

For example, I feel that C# (especially LINQ via C# 3+) is becoming much more expressive. This LINQ statement is a great example:

var results = collection.Where(item => item > 5);

Without knowing the details of the language or the implementation being used, the developer intent is (in my opinion) very clear in the above statement.

I do not think that the verboseness of the language is equal to its expressiveness, however, there is some correlation in place. If a language requires a lot of code in order to express an abstraction, it is less expressive. These are two related, but different, concepts.

The same is true with power - although here a language's features (ie: power) must be complete enough to express the abstraction clearly. Without this, expressiveness will suffer. That being said, a language can be very "powerful" in terms of features, but not necessarily be expressive, if the feature set is difficult to understand.

Answer 3

Wikipedia has a bit about the concept. I myself take it to mean that a language can accomplish more with less (the so called "informal usage" in the Wikipedia article).

I consider JavaScript expressive (though this could be because Douglas Crockford drilled that idea into my noggin) because it can do so much with just a few keywords. For instance, the function keyword is a function, as well as a method, a class, and a lambda.

Some code illustration (leaving out some details for brevity) in JavaScript. It's an event class I wrote:

SJJS.util.Event = (function() {
    var _listeners = [];
    var _listenerReturns = [];

    return {
        addDomListener: function(element, eventName, listener) {
        },
        trigger: function(element, eventName) {
        },
        removeListener: function(eventlistener) {
        }
    }
})();

With just function, var, and some curly braces and parentheses I made a static class with methods and private variables.

Answer 4

For me is the ability that the language has to clearly express my logic and ideas through code, in a way that somebody else reading the code I've wrote can easily figure out what I was thinking about when I did it.

Answer 5

I always took it to be roughly equivalent to how high-level a language is. If you wanted to try to quantify expressiveness, the units would be something like "machine code instructions per language statement"

A more expressive language might be very good at doing rather a lot of work without writing a lot of code. However, it would probably be more domain-specific and a wee bit slower for some tasks than a less expressive one.

Answer 6

If you want an answer that's somewhat theoretical but more rigorous than most, you might want to look around for Matthias Felleisen's On the Expressive Power of Programming Languages. I'm pretty sure a bit of looking around the net will turn up at least a few copies.

If you want a more practical answer of what most people really mean when they say it, that's, frankly, rather different. Usually, at least in my experience, an "expressive" language means: "I like the language, but can't cite any objective support for doing so." Conversely, things like "less expressive", or "not expressive" generally mean: "I don't like the language [as well], but can't cite any objective support for doing so."

"Not expressive" is often similar to a politician accusing another of being "fascist" -- clearly pejorative, but without any meaningful definition of what's supposedly wrong.

One of the big problems stems from a fundamental difference of opinion. There are at least two fundamentally different general ideas that people seem to have about expressiveness:

1. the ability to express a wide variety of ideas.
2. the ability to express some specific ideas clearly (and often succinctly).

To consider some extreme examples, assembly language would qualify as highly expressive by the first criteria--you can do essentially anything in assembly language that you can in a higher level language, and you can do some things in assembly language that you can't in essentially any higher level language.

Obviously, assembly language doesn't look nearly so good by the second measure--it typically requires quite a large amount of fairly opaque code to accomplish much of anything. This measure would tend to favor a language like Haskell or APL, to give only a couple of examples.

These two notions of what "expressive" means are frequently close to diametrically opposed. The first tends to favor the "lowest" level languages, while the second tends to favor the "highest" level. By combining the two, it's pretty trivial to choose a definition that "proves" that a language of your choice is the most expressive.