Functional Reactive Animation

Appeared in ICFP 1997

Conal Elliott and Paul Hudak


Fran is a collection of data types and functions for composing richly interactive, multimedia 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 conditions, carrying possibly rich information. Most traditional values can be treated as behaviors, and when images are thus treated, they become animations. Although these notions 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 reasoning and implementation. A method to effectively and efficiently perform event detection using interval analysis is also described, which relies on the partial information structure on the domain of event times. Fran has been implemented in Hugs, yielding surprisingly good performance for an interpreter-based system. Several examples are given, including the ability to describe physical phenomena involving gravity, springs, velocity, acceleration, etc. using ordinary differential equations.

In 2007, this paper was awarded as the most influential paper of ICFP ’97.


   title        = {Functional Reactive Animation},
   url          = {},
   author       = "Conal Elliott and Paul Hudak",
   booktitle    = "International Conference on Functional Programming",
   year         = 1997

See also: A Brief Introduction to ActiveVRML, describing a predecessor of Fran with the same basic components and semantic model.