My own Objective-Smalltalk.

Here with a more traditionally interactive environment (so updates are applied when you save the method): https://www.youtube.com/watch?v=ArcClqt2vTc

Here in a really live environment I call CodeDraw, with updates computed on every keystroke (the "Run" button is just left-over UI, it doesn't do anything): https://www.youtube.com/watch?v=sypkOhE-ufs

Most interpreted or incrementally compiled systems should be able to do this.