. Graphical user interfaces (GUIs) are hard to combine with functional programming. Using a suitable combination of monads, we are able to tame the imperative aspects of graphical I/O in a straightforward and elegant way. We present a concept to integrate lightweight GUIs into the functional framework, together with a library of basic functions and layout combinators to manipulate the GUI. An implementation of this library, using a set of high-level graphical I/O routines, is outlined. Examples demonstrate the simple way in which applications can be written. 1 Introduction Everybody wants to use graphical user interfaces. And everybody wants to use functional programming languages. Unfortunately, these concepts are hard to combine: I/O, and graphical I/O in particular, is imperative in nature, and thus contradictory to the functional paradigm. Our goal is to reconcile these two concepts, by developing a framework in which a functional programmer smoothly can provide his program with a...

Research into wireless data networks with mobile nodes has

. The initial-algebra approach to modelling datatypes consists of giving constructors for building larger objects of that type from smaller ones, and laws identifying di#erentways of constructing the same object. The recursive decomposition of objects of the datatype leads directly to a recursive pattern of computation on those objects, whichisvery helpful for both functional and parallel programming. We showhow to model a particular kind of directed acyclic graph using this initial-algebra approach. Keywords. Graphs, data types, catamorphisms, initial algebras, Bird-Meertens Formalism, program derivation. 1 Introduction It is now widely recognized that the traditional ad-hoc approaches to program construction do not yield reliable software; a more systematic and formal approach is required. One such approach consists of program veri#cation---proving after the fact that a given program satis#es its formal speci#cation. This approach turns out to be di#cult to implement, not lea...

Many popular myths have evolved about functional programming languages and their power of expression; one such myth is that "functional languages cannot construct arbitrary cyclic data structures at run-time" and therefore that functional languages are not appropriate for problems which require efficient representations of dynamically-specified cyclic graph structures (such as a route-finding robot in a maze). This myth persists despite ample published work to the contrary (see for example [All89]) and is a recurring subject of debate [USE]. We provide a survey of some of the related work in this area; we then build on this work by presenting methods for both the dynamic construction of complex cyclic structures and their direct manipulation using circular programming techniques. 1 Introduction "A" "B" "C" "D" Figure 1: A small, directed, cyclic graph If one were asked to use a functional language to construct the directed graph given in Figure 1 then the resulting code might typically...

Introduction This chapter initially considers pure lazy functional languages: their philosophy, advantages and disadvantages. We then examine how to develop efficient lazy functional programs. One way to achieve efficiency is to introduce impurities. In the final section the two schools of lazy functional programming, pure and impure, are assessed. The assessment centres around two partial implementations of the Hopcroft Tarjan graph planarity algorithm. Profiling tools are used to make an experimental comparison and optimisation of each program. 4.1 Lazy Functional Programming In his book [42] Reade suggests that the user of a traditional imperative language is required to do the following: 1. describe the result to be computed; 2. impose an order on the steps required in the computation; 3. create and destroy, as required, any data structures used by the computation. 74 The first item is concerned with the extensional prope