Functional Reactive Animation

Abstract

Fran (Functional Reactive Animation) is a collection of data types and functions for composing richly interactive, multi-media animations. The key ideas in Fran are its notions of behaviors and events. Behaviors are time-varying, reactive values, while events are sets of arbitrarily complex condi-tions, carrying possibly rich information. Most traditional values can be treated as behaviors, and when images are thus treated, they become animations. Although these no-tions are captured as data types rather than a programming language, we provide them with a denotational semantics, including a proper treatment of real time, to guide reason-ing and implementation. A method to eectively and ef-ciently perform event detection using interval analysis is also described, which relies on the partial information struc-ture on the domain of event times. Fran has been imple-mented in Hugs, yielding surprisingly good performance for an interpreter-based system. Several examples are given, in-cluding the ability to describe physical phenomena involving