Functional Programming and Virtual Worlds

The FunWorlds project aims to combine and integrate ideas from functional programming, in particular functional reactive programming a la Fran, and virtual worlds, as exemplified by the Virtual Reality Modeling Language (VRML’97). The goal of our research is the design of a concrete toolkit offering functional programmers access to this rich medium for communication and interaction while introducing virtual reality scene authors to an expressive high-level modeling paradigm. In earlier work, reported at IFL’2001, we experimented with mapping Fran concepts into VRML’97, using a domain-specific embedded compilation approach to map high-level programs in a Haskell DSEL into standard VRML’97 + ECMAScript worlds, renderand navigable using any VRML’97 browser. The present paper is concerned with a more direct integration, based on Sven Panne’s HOpenGL Haskell binding to the industry standard for 2d and 3d graphics, OpenGL. To enable a declarative approach, we first introduce a simple scene graph similar to the static aspects of VRML, which is translated into calls to the imperative HOpenGL API. To address dynamic aspects of our scenes, we build on ideas taken from Conal Elliott’s Fran (functional reactive animation). However, Fran itself has gone through a series of implementations of increasing complexity and difficult-to-predict performance. We trace some of those problems to issues in the design of the Fran DSEL and choose to deviate from this original Fran design in several points. Without unduly restricting expressiveness, our more pragmatic design leads to a drastically simplified implementation offering competitive, and more importantly, predictable performance.