This is much better than smalltalk. In Smalltalk, you could just edit code on the fly, but nothing would happen if that code wasn't continuously executing in an infinite loop. LightTable, on the other hand, supports real liveness. Its something that we never got in Smalltalk or Lisp.

Edit: Morphic (from Self) does support liveness, but only when it is being edited at the graphical level. If you are editing code, you are stuck in the same refresh trap as Smalltalk or Lisp, but to be fair, morphs are continuously updating themselves in infinite loops so it doesn't matter :)