What does "expressive" mean when referring to programming languages?

Question

I hear this word a lot in sentences like "javascript is a very expressive language". Does it just mean there aren't a lot of rules, or does "expressive" have a more specific meaning?

Answer 1

'Expressive' means that it's easy to write code that's easy to understand, both for the compiler and for a human reader.

Two factors that make for expressiveness:

• intuitively readable constructs
• lack of boilerplate code

Compare this expressive Groovy, with the less expressive Java eqivalent:

3.times {    println 'Hip hip hooray' } 

vs

for(int i=0; i<3; i++) {     System.out.println("Hip hip hooray"); } 

Sometimes you trade precision for expressiveness -- the Groovy example works because it assumes stuff that Java makes you to specify explicitly.

Answer 2

I take it to mean that it's capable of expressing ideas/algorithms/tasks in an easy-to-read and succinct way.

Usually I associate a language being expressive with syntactic sugar, although that's not always the case. Examples in C# of it being expressive would be:

• foreach (instead of explicitly writing the iteration)
• the using statement (instead of explicitly writing the try/finally)
• query expressions (simpler syntax for writing LINQ queries)
• extension methods (allowing chaining of method calls, again primarily for LINQ)
• anonymous methods and lambda expressions (allowing easier delegate and expression tree construction)

A different example would be generics: before C# got generics, you couldn't express the idea of "an ArrayList containing only strings" in code. (You could document it, of course, or write your own StringList type, but that's not quite the same.)