Theorie"en voor het berekenen van algoritmen (met een samenvatting in het Nederlands) PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Rijksuniversiteit te Utrecht op gezag van de Rector Magnificus, Prof. Dr. J.A. van Ginkel ingevolge het besluit van het College van Dekanen

The interface with the outside world has always been one of the weakest points of functional languages. It is not easy to incorporate I/O without being allowed to do side-effects. Furthermore, functional languages allow redexes to be evaluated in any order while I/O generally has to be performed in a very specific order. In this paper we present a new solution for the I/O problem which we have incorporated in the language Concurrent Clean. Concurrent Clean offers a linear type system called Unique Types . It makes it possible to define functions with side-effects without violating the functional semantics. Now it is possible to change any object in the world in the way we wanted: e.g. arrays can be updated in-situ, arbitrary file manipulation is possible. We have used this powerful tool among others to create a library for window based I/O. Using an explicit environment passing scheme provides a high-level and elegant functional specification method for I/O, called Event...

At first sight, I/O in a pure functional language is not as straightforward as in imperative languages. For some years work has been going on to alleviate these problems, and there are now a number of different approaches. The purpose of this report is twofold --- firstly we shall review the problems encountered in performing I/O in a functional language and look at some of the ways these might be conquered, and secondly we shall look at some more recent solutions to I/O which encompass graphical interfaces.

I/O mechanisms are needed if functional languages are to be suitable for general purpose programming and several implementations exist. But little is known about semantic methods for specifying and proving properties of lazy functional programs engaged in I/O. As a step towards formal methods of reasoning about realistic I/O we investigate three widely implemented mechanisms in the setting of teletype I/O: synchronised-stream (primitive in Haskell), continuationpassing (derived in Haskell) and Landin-stream I/O (where programs map an input stream to an output stream of characters) . Using methods from Milner's CCS we give a labelled transition semantics for the three mechanisms. We adopt bisimulation equivalence as equality on programs engaged in I/O and give functions to map between the three kinds of I/O. The main result is the first formal proof of semantic equivalence of the three mechanisms, generalising an informal argument of the Haskell committee. 1 Introduction and motivation...

This paper uses the Fran system for functional reactive animation to give a simulation of a lift -- or elevator -- with many floors. The paper first introduces a two-floor version, and then indicates in detail how this is extended to give a simulation with an arbitrary number of floors and featuring more realistic animated graphics.

The functional programming language Haskell is examined from the point of view of proving programs correct. Particular features explored include the data type definition facilities, classes, the behaviour of patterns and guards and the monad approach to IO in the Glasgow Haskell compiler. 1 Introduction Haskell [Hudak et al., 1992, Hudak and Fasel, 1992] is a lazy functional programming language which is likely to become a de facto as well as a de jure standard academically and commercially. It is often said that a crucial part of the appeal of functional languages is the ease with which proofs concerning functional programs can be written. It is also widely accepted that if proof is to be taken seriously, it needs to be formalised, and to be checked by machine 1 . The aim of this paper is to initiate discussion on the form that a logic for Haskell might take. It is based to some degree on the author's previous work on devising a logic for Miranda, [Thompson, 1989], which in turn b...

The research presented in this thesis is about the design and implementation of Naira, a parallel, parallelising compiler for a rich, purely functional programming language. The source language of the compiler is a subset of Haskell 1.2. The front end of Naira is written entirely in the Haskell subset being compiled. Naira has been successfully parallelised and it is the largest successfully parallelised Haskell program having achieved good absolute speedups on a network of SUN workstations. Having the same basic structure as other production compilers of functional languages, Naira's parallelisation technology should carry forward to other functional language compilers. The back end of Naira is written in C and generates parallel code in the C language which is envisioned to be run on distributed-memory machines. The code generator is based on a novel compilation scheme specified using a restricted form of Milner's ß-calculus which achieves asynchronous communication. We present the f...

In this paper we present a functional interleaved Event I/O system. This system is a generalization of the Event I/O system as incorporated into the lazy, purely functional programming language Clean. The Inter leaved Event I/O system offers features that are more commonly found outside the functional scene. These features are dynamic process creation, and two well-known forms of inter-process communication: asynchronous message passing, and data sharing. Both forms of communication are polymorphic and type-safe. As we are working in a functional language, messages can contain higher-order functions and arbitrarily complex algebraic types. Communication by data sharing is a restricted form of communication by global data structures. Nevertheless, the new system is still completely functional because the generalization is done within the pure functional framework. The Interleaved Event I/O system has been implemented and will become part of the new release of Clean. 1 Introduction R...

Incremental computations can improve the performance of interactive programs such as spreadsheet programs, program development environments, text editors, etc. Incremental algorithms describe how to compute a required value depending on the input, after the input has been edited. By considering the possible different edit actions on the data type lists, the basic data type used in spreadsheet programs and text editors, we define incremental algorithms on lists. Some theory for the construction of incremental algorithms is developed, and we give an incremental algorithm for a more involved example: formatting a text. CR categories and descriptors: D11 [Software]: Programming Techniques --- Applicative Programming, D43 [Software]: Programming Languages --- Language constructs, I22 [Artificial Intelligence]: Automatic Programming --- Program transformation. General terms: algorithm, design, theory. Additional keywords and phrases: Bird-Meertens calculus for program construction, incremen...

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