This note continues an exploration of arrow-friendly formulations of functional reactive programming. I refine the previous representations into an interactive dance with dynamically interchanging roles of follow and lead. These two roles correspond to the events and reactive values in the (non-arrow) library Reactive described in a few previous posts. The post ends with some examples.
In a few recent posts, I’ve been writing about a new basis for functional reactive programming (FRP), embodied in the Reactive library. In those posts, events and reactive values are (first class) values. A reactive system able to produce outputs from inputs might have type
Event a -> Event b or perhaps
Reactive a -> Reactive b.
Although I’m mostly happy with the simplicity and expressiveness of this new formulation, I’ve also been thinking about arrow-style formulations, as in Fruit and Yampa. Those systems expose signal functions in the programming interface, but relegate events and time-varying values (called “behaviors” in Fran and “signals” in Fruit and Yampa) to the semantics of signal functions.
If you’re not familiar with arrows in Haskell, you can find some getting-started information at the arrows page.
This post explores and presents a few arrow-friendly formulations of reactive systems.
- 2008-02-06: Cleaned up the prose a bit.
- 2008-02-09: Simplified chatter-bot filtering.
- 2008-02-09: Renamed for easier topic recognition (was “Invasion of the composable Mutant-Bots”).
- 2008-02-10: Replaced
compsby the simpler
concatMBfor sequential chatter-bot composition.