Thank you for this post - I hadn't seen Bret Victor's essay before. On a side note, your bookshelf link is broken (it contains a > at the end). It should be:

Thank you for this post - I hadn't seen Bret Victor's essay before. On a side note, your bookshelf link is broken (it contains a > at the end). It should be: http://img823.imageshack.us/img823/7795/screenshot20120731at120.png http://img823.imageshack.us/img823/7795/screenshot20120731at...