This is the third part of a small series of articles1 on how to use Haskell for the development of Cocoa applications. In this post I describe a simple way how to implement a Cocoa controller in Haskell. This way one can define the application’s model layer completely in Haskell without any reference to the underlying Cocoa framework (or Objective-C classes). Recap: OBJC InstancesSince the last bl