Abstract

this paper. It is important not only to "back up" variables to their previous values, but also to "back up" a consistent view of the user interface, including static code, dynamic data, and graphical output so that the user "backs up" their mental image of the program execution. The reversible control structure aspects of ZStep 95 are discussed in more detail in [9]. We will address the issue of the computational expense of the historykeeping mechanism later. ZStep 95's main menu uses a bi-directional "video recorder" metaphor. The single-arrow "play" and "reverse" correspond to single-step in a traditional stepper, and the "fast-forward" and "rewind" operation go from an expression to its value and vice versa, without displaying details.

Citations