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 the verboseness/succinctness? I mean, if one language can write down something shorter than the other, does that mean expressiveness? Please refer to my other question - Article about code density as a measure of programming language power
• Is it the power of the language? Paul Graham says that one language is more powerful than the other language in a sense that one language can do that the other language can't do (for example, LISP can do something with macro that the other language can't do).
• Is it just something that makes life easier? Regular expression can be one of the examples.
• Is it a different way of solving the same problem: something like SQL to solve the search problem?

What do you think about the expressiveness of a programming language? Can you show the expressiveness using some code?

What's the relationship with the expressiveness and DSL? Do people come up with DSL to get the expressiveness?

Answer 1

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.