Fudgets

Abstract: The powerful abstraction mechanisms of functional programming languages provide the means to develop domain-specific programming languages within the language itself Typically, this is realised by designing a set of combinators (higher-order reusable programs) for an application area, and by constructing individual applications by combining and coordinating individual combinators This paper is concerned with a successful example of such an embedded programming language, namely Fudgets, a library of combinators for building graphical user interfaces in the lazy functional language Haskell The Fudget library has been used to build a number of substantial applications, including a web browser and a proof editor interface to a proof checker for constructive type theory This paper develops a semantic theory for the non-deterministic stream processors that are at the heart of the Fudget concept The interaction of two features of stream processors makes the development of such a semantic theory problematic: (i) the sharing of computation provided by the lazy evaluation mechanism of the underlying host language, and (ii) the addition of non-deterministic choice needed to handle the natural concurrency that reactive applications entail We demonstrate that this combination of features in a higher-order functional language can be tamed to provide a tractable semantic theory and induction principles suitable for reasoning about contextual equivalence of Fudgets

Abstract: In this paper we describe the implementation of several graphical programming paradigms (Model View Controller, Fudgets, and Functional Animations) using the GUI library TkGofer. This library relies on a combination of monads and multiple-parameter type classes to provide an abstract, type safe interface to Tcl/Tk. We show how choosing the right abstractions makes the given implementations surprisingly concise and easy to understand.

Abstract: Carlsson and Hallgren [1] describe the implementation of a set of “functional widgets” (Fudgets): components for programming graphical user interfaces under the X window system using the non-strict functional programming language Haskell. We describe an alternative implementation based on existing widget sets (currently Openlook and Motif). Our purpose is twofold: to show that the Fudgets approach can be applied to existing widget sets; and to discuss problems experienced with Fudgets during an industrial case study.

Abstract: The Fudgets system is a toolkit for developing graphical applications in the lazy functional programming language Haskell. In this paper we develop an operational semantics for a subset of this system, inspired by ideas from concurrency theory. A semantic theory based on bisimulation is defined and shown to be a congruence. We consider two applications of this theory: firstly, some equational rules useful for reasoning about Fudget programs are verified; secondly, we show how the operational semantics can be used to check the correctness of implementations of the Fudgets system.