Simply efficient functional reactivity

I submitted a paper Simply efficient functional reactivity to ICFP 2008.


Functional reactive programming (FRP) has simple and powerful semantics, but has resisted efficient implementation. In particular, most past implementations have used demand-driven sampling, which accommodates FRP’s continuous time semantics and fits well with the nature of functional programming. Consequently, values are wastefully recomputed even when inputs don’t change, and reaction latency can be as high as the sampling period.

This paper presents a way to implement FRP that combines data- and demand-driven evaluation, in which values are recomputed only when necessary, and reactions are nearly instantaneous. The implementation is rooted in a new simple formulation of FRP and its semantics and so is easy to understand and reason about.

On the road to efficiency and simplicity, we’ll meet some old friends (monoids, functors, applicative functors, monads, morphisms, and improving values) and make some new friends (functional future values, reactive normal form, and concurrent “unambiguous choice”).

"Tangible Functional Programming" — icfp version

ICFP ’07 paper draft — comments please

Warning: if you’re on the ICFP program committee and want to preserve double-blind reviewing, please ignore this post.

I’ve been working on an ICFP paper called “Tangible Functional Programming”, revising my last year’s submission on Eros. If you’re interested in taking a look, I’d greatly appreciate any comments, especially before the April 6 submission deadline.


We present a user-friendly approach to unifying program creation and execution, based on a notion of “tangible values” (TVs), which are visible and interactive GUI manifestations of pure values. Programming happens by gestural composition of TVs. Our goal is to give end-users the ability to create parameterized, composable content without imposing the usual abstract and linguistic working style of programmers. We hope that such a system will put the essence of programming into the hands of many more people, and in particular people with artistic/visual creative style.

In realizing this vision, we develop algebras for visual presentation and for “deep” function application, where function and argument may both be nested within a structure of tuples, functions, etc. Composition gestures are translated into chains of combinators that act simultaneously on statically typed values and their visualizations.

Here is a figure from the paper, showing one stage of an interactively composed interactive 2D region. The user selects compatibly-typed input and output widgets, typically in different TVs. The result is a new TV that merges the source TVs, except for the connected input and output, which vanish. The sliders control the disk and checker sizes and the checker’s rotation angle.

Edit on March 28:I just added two relevant pointers to the paper’s web page: