Code playbacks allow instructors to create guided code walkthroughs showing how their code evolves from start to finish. Playback authors create narratives explaining their thought processes and students get to see reasoning behind each decision. The narrative can include visual feedback including whiteboard-style pictures, screenshots of output, and videos describing what the code is doing.

This paper describes a tool to help instructors guide learners through code examples. The tool captures low-level changes made to a group of files using a popular code editor. Then it allows the programming session to be replayed so that an author can annotate the evolution of the code and explain the reasons behind important decisions. The author-supplied narrative can include text, code highlights, media (hand-drawn pictures, screenshots, videos, and audio files), and self-grading questions. The combination of the narrative and the evolving code is called a code 'playback'. Playbacks are viewable in a web browser.

There is value in instructors guiding students through complex programming problems. An instructor can describe how they start a program, decide what to do next, recover from poor problem-solving choices, and check their work. Worked examples give students an inside look at an expert's mental model and show how an expert approaches a problem.

There is value in instructors guiding students through complex programming problems. An instructor can describe how they start a program, decide what to do next, recover from poor problem solving choices, and check their work. Worked examples give students an inside look at an expert/s mental model and show how an expert approaches a problem. Live coding demonstrations of complex problems can be difficult for instructors to do well, however. This demonstration will show a tool that allows programmers to guide an audience through the evolution of some code without requiring a live performance. The open source tool, Storyteller (https://github.com/markm208/storyteller), integrates with a popular text editor to record all file editing and file operations so that they can be replayed in an animated, annotated playback. Instructors can replay their work to reflect on it. They can insert comments (text, drawings, screenshots, and audio) to describe their code and to explain the reasons why certain decisions were made. These comments are linked not only to a place in the code but to a point in time during the evolution of the code. The comments are recorded and are visible in future playbacks of the code. The author of a playback can create a narrative describing how and why their code is changing. These can be used by instructors to provide worked examples for their students. The demonstration will show some example playbacks and how they were used in class along with how to create and share playbacks with the tool.

Software systems evolve over time. Currently we do not do a good job of documenting this evolution. This essay discusses the need to better document software evolution and introduces the Moving Picture Metaphor. Source Control Management systems are more like collections of still photographs than moving pictures. Still photography is not ideal when trying to capture evolutional changes. Moving pictures do a much better job. A storyteller can use moving pictures to tell compelling stories that are easier to digest than traditional documentation. We can learn a great deal from watching stories that document a system's evolution.