Steering programs via time travel

The environments that programmers traditionally use for problem-solving-with separate modes and tools for writing, compiling, testing, visualizing and debugging-derive their basic structure from historical accident, and take little advantage of human-computer interaction (HCI) research into the cognitive issues of programming. We believe that neglect of these issues impedes programmers' ability to produce reliable, maintainable software. Visual programming languages (VPLs) have begun to address this problem by creating more flexible, less modal programming environments, and we have taken a step further in this direction. In this paper, we describe a VPL in which programmers can modelessly steer as they specify, visualize, explore and alter the behavior of a program while traveling through the program's logical time. This approach supports two often-neglected cognitive principles that HCI research shows can help programmers in their problem-solving.