A modern programming language that makes developers happier.

kotlinlang

<@U0BDMQTHS>, <@U2AN5KYLX> there is a support for completion, at least in 1.1, and there will be some more improvements. 
The simple repl without fancy editing features is relatively easy to extract - you may find an example in `kotlin-jupyter` project. And quite likely we’ll add a library with required components for making it even easier soon.
As of an advanced one - we are thinking about it, but cannot promise anything for the next release yet.