Functional interactive behavior
In a previous post, I presented a fundamental reason why classic FRP does not fit interactive behavior, which is that the semantic model captures only the influence of time and not other input. I also gave a simple alternative, with a simple and general model for temporal and spatial transformation, in which input behavior is transformed inversely to the transformation of output behavior.
The semantic model I suggested is the same as used in “Arrow FRP”, from Fruit and Yampa. I want, however, a more convenient and efficient way to package up that model, which is the subject of the post you are reading now.
Next, we took a close look at one awkward aspect of classic FRP for interactive behavior, namely the need to trim inputs, and how trimming relates to comonadic FRP.
The trim function allows us to define multi-phase interactive behaviors correctly and efficiently, but its use is tedious and is easy to get wrong.
It thus fails to achieve what I want from functional programming in general and FRP in particular, which is to enable writing simple, natural descriptions, free of mechanical details.
The current post hides and automates the mechanics of trimming, so that the intent of an interactive behavior can be expressed directly and executed correctly and efficiently.