With the introduction of concurrent functional languages, potential non-determinism is introduced. Two processes can update a file at the same time, leading to an unpredictable result. This is taken for granted, there is a common idea stating that concurrency and nondeterminism are synonymous. In their paper, Carter and Holyer [11] propose a deterministic approach to many systems which are inherently non-deterministic. The first steps in that direction have been taken with the design of BriX, a deterministic concurrent windowing system. This report describes the development and workings of this system. Special efforts were taken on the avoiding of non-determinism. BriX was not designed to be a standard windowing system, the goal was to write it with deterministic techniques. Contents 1 Introduction 1 2 Monadic I/O 2 2.1 Implementation : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 3 2.2 State Encapsulation : : : : : : : : : : : : : : : : : : : : : : : : : : ...