FranTk -- a declarative GUI language for Haskell. FranTk is a new high level library for programming Graphical User Interfaces (GUIs) in Haskell. It is based on Fran (Functional Reactive Animation), and uses the notions of Behaviors and Events to structure code. Behaviors are time-varying, reactive values. They can be used to represent the state of an application. Events are streams of values that occur at discrete points in time. They can be used, for instance, to represent user input. FranTk allows user interfaces to be structured in a more declarative manner than has been possible with previous functional GUI libraries. We demonstrate, through a series of examples, how this is achieved, and why it is important. These examples are elements of a prototype, Air Traffic Control simulator. FranTk uses a binding to the popular Tcl/Tk toolkit to provide a powerful set of platform independent set of widgets. It has been released as a Haskell library that runs under Hugs and GHC.

This software is also peer reviewed by journal TOMS.