User Interfaces for Live Programming

Live programming eliminates the gulf between code and execution. To design live programming systems, we first need to understand what we are developing. Once we gain domain-specific knowledge of the target applications, we create user interfaces to edit the running application, such as scrubbing sliders, color palettes, and timeline interfaces. The key to the fluid programming experience of live programming is the combination of deep understanding of the target applications and adoption of interactive user interfaces.

This tutorial introduced the history of live programming research and examined its significance from different perspectives by reviewing related tools and practices proposed in research and used in visual art.

Technically speaking, the pursuit of "liveness" in programming systems reached a milestone in the 1990s, when many visual programming systems employing dataflow languages and environments, including VIVA, were researched and developed to allow interactive editing of programs, and a framework for user interface development in Smalltalk-based systems, Morphic, appeared. However, with the exception of Spreadsheet, visual programming did not become mainstream, and general-purpose object-oriented languages and integrated development environments, which were in some ways degraded from Smalltalk, gained popularity.

We had to wait until the 2010s to see a renewed interest in "liveness" in the programming experience, when Bret Victor's "Inventing on Principle" talk with many appealing demonstrations took place and the Workshop on Live Programming was held for the first time. Here I see "liveness" as a kind of user experience that can be achieved by building a ladder of abstraction from an abstract programming language to a concrete program execution state, and individual technical components such as a single programming language design or a single tool design do not seem to be sufficient. At the heart of the design of live programming systems is the design of the user interface, which is tailored to the domain-specificity of the applications to be developed in the programming system. From this perspective, visual programming environments for designers and tools for the visual arts have been successful for a long time, and more recently, there have been an increasing number of live programming systems specialized for diverse application domains.

For this tutorial, please also see the corresponding page on Scrapbox (Wiki site; Japanese) and the hands-on documentation on GitHub (Japanese). Also, for future perspectives not covered in depth in the tutorial, please refer to my keynote at LIVE 2017.

Live Programming systems provide concrete information about how the program behaves when it is executed. With help of this concrete information, programmers can easily iterate on editing and testing the program behavior.

Please note that the origin of Live Programming is not new as you can see early examples in visual programming and object-oriented programming environments. Then, why is it attracting much attention these days? In short, I consider it is because of its focus on the user experience.

From now on, I will discuss three perspectives on user interface design of Live Programming systems and interesting directions to explore in each.

Programming with End-users

As Live Programming systems provide interactive and intuitive user interfaces for debugging and editing programs, some of the user interfaces can be exposed to the end-users so that they can customize the programs as they wish. [Live Tuning]

When the provided user interfaces cannot satisfy their needs, they can still submit requests to programmers with rich contextual information provided by the Live Programming systems. [User-Generated Variables]

Live Programming techniques benefit not only programmers, but also end-users, and enable Programming as Communication.

Programming this Material World

Live Programming often targets simple applications such as drawing graphics. In contrast, "software is eating the world" and there are complex and interesting applications such as physical computing and virtual reality.

Their actual "framerate" can be very slow; e.g. printing device enclosures and producing scent. Emulating, or sometimes even pretending, is needed to provide the continuous feedback.

Making full use of five senses in programming environments would be crucial in the near future.

Programming with Time Travel

Live Programming puts focus on providing live feedback to the programmer, but it does not always mean providing realtime information of the running program.

The timeline interface and record and replay features together provide time traveling experience and play an important role to find critical timings in the history. Once the timing of interest is found, editing the code and program input would update the program output, allowing the programmer to explore future"s."

The following projects implement or discuss Live Programming experiences.