The design space for a given application, even one that has been tightly specified, is enormous. Prototyping has become an accepted and effective tool for evaluating user interface designs. However, the ability to rapidly change the user interface to explore large sections of the design space is limited by commonly used programming languages and environments.

The Juxtapose programming environment helps us to break through these limitations in two ways: first, by permitting parallel editing and execution to compare code alternatives, and, second, by the automated generation of a control interface that supports tuning of application program parameters. This work is set in various contexts: desktop applications, smart phones, and physical computing interfaces. Not only is the use and significance of Juxtapose explained well in this work, but it also describes a small usability experiment that verifies the utility of this system, and points out areas of needed improvement. This well-written report about Juxtapose gives a reasonable overview of related work, and presents a balanced view of this tool.