TclProp: A Data-Propagation Formula Manager for Tcl and Tk

TclProp is a data propagation formula manager for Tcl and Tk. It supports and enforces one-way declarative relationships among variables. If, for example, we enter the formula A = B + C, whenever B or C changes, A is also updated to reflect the new sum. TclProp also supports triggers -- code to be executed when one of a set of variables changes. And, TclProp includes a mechanism for linking variables to object attributes (e.g., the enabled/disabled status of a button) so these attributes can be used in formulas and triggers. This paper presents an example of how data propagation formulas can simplify programming and presents the design and implementation of TclProp 1.0, an implementation built in Tcl.