This technique can be used to let the compiler literally drive the development of a given feature or bugfix, including the design and necessary behavior.

It consists of 2 basic steps:

• Break something! Break a very specific place in the code by changing some type or signature that is downstream from all potentially changing code. Introduce a breaking change that expresses the feature or bugfix you want to have.
• Then follow compiler errors! Just go through all compiler errors and fix them in accordance with your objectives. Fix all errors in isolation and as minimally as possible. Note however, that you must make sure that code that compiles is semantically complete! You can not introduce anything that can be used to make something compile without it being correct!

The actual feature request for this example is: Thread through all the backend messages without changing the code structure so that they appear on the frontend.

Remember, you have to change exactly one thing, and then just follow compiler errors! The solution given in the accompanying talk is in the solution branch.