Lambda the Ultimate

Project Lamdu, a live-programming environment with a little something for everyone, including things like:

• ...the canonical representation of programs should not be text, but rich data structures: Abstract syntax trees.
• Effect Typing... ...allows a live environment to actually execute code as it is being edited, safely, and bring the benefits of spreadsheets to general purpose programming
• When types are rich enough, much of the program structure can be inferred from the types.
• Integrated revision control and live test cases will allow "Regression Debugging".