[rdtsc]

To a new and experimental language it would be a small change. Try adding a built-in map to C or Java. Lambda expressions took year to add to Java for example.

Now if say Nimrod or Dart acquired built-in sets (I don't know maybe it already does) it wouldn't be too remarkable. They are pretty experimental.

Also there is a difference between having a library and a language built-in. All those languages including Erlang, have libraries that provide associative data structures.

[NigelTufnel]

I don't understand. By built-in map you mean "map literals"?

[rdtsc]

Yes, as built-ins I consider literals (with specific language syntax). Well, otherwise most modern useful languages have at least a library level implementation of some associative data structures. Erlang has them too, dict, gb_tree and a few others.