We're building tonicdev.com (similar to iPython/Swift Playgrounds). A lot of these ideas are very difficult in the general case. For just one example, we spent

We're building tonicdev.com (similar to iPython/Swift Playgrounds). A lot of these ideas are very difficult in the general case. For just one example, we spent a long time reasoning about time traveling (and came up with what we think is a great model for it - which takes into account the entire system including the filesystem, but it took considerable engineering effort and bleeding edge OS tools like CRIU: http://blog.tonicdev.com/2015/09/10/time-traveling-in-node.js-notebooks.html http://blog.tonicdev.com/2015/09/10/time-traveling-in-node.j... )