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.

This thesis describes an implementation of a small window-based graphical user interface toolkit for the X Window System written in the lazy functional language LML. By using this toolkit, a Haskell or LML programmer can create a user interface with menus, buttons and other graphical interface objects, without conforming to more or less imperative programming paradigms imposed if she were to use a traditional (imperative) toolkit. Instead, the power of the abstraction methods provided by Haskell or LML are used. The main abstraction we use is the fudget. Fudgets are combined in a hierarchical structure, and they interact by message passing. The current implementation is based on a sequential evaluator, but by using nondeterminism and oracles, we suggest how fudgets can evaluate in parallel. We believe that the toolkit can be extended to a full-feathered and practically useful high level graphical toolkit. ISBN 91-7032-841-2 i No one can have experienced to the fullest the true sense ...