I have seen a video showing a real time debugging tool for vs2012. It allows you to code and debug at the same time ! In the video, they implemented "Quick Sort", by editing "conditions for if statement" and "the index of array". Hover your mouse over a variable, the value will be evaluate on sight. Then, the programmer can discover whether the condition in algorithm is smaller or bigger.
Unfortunately, I forgot its link. It something like 'Light Table', which enable you to see the result of code by hovering your mouse onto the variable name.
It's really cool. Where is it ? Any clues will help.
Are you thinking of something like this or this?
They're both inspired by Bret Victor's great talk Inventing on Principle