Abstract Genuinely Functional User Interfaces

Fruit is a new graphical user interface library for Haskell based on a formal model of user interfaces. The model identifies signals (continuous time-varying values) and signal transformers (pure functions mapping signals to signals) as core abstractions, and defines GUIs compositionally as signal transformers. In this paper, we describe why we think a formal denotational model of user interfaces is useful, present our model and prototype library implementation, and show some example programs that demonstrate novel features of our library.