In particular, "distance" in software is surely a function of "distance in mental space", rather than simply the number of lexical-scope boundaries crossed, or

In particular, "distance" in software is surely a function of "distance in mental space", rather than simply the number of lexical-scope boundaries crossed, or the specific number of containing modules. Do we have some way of formalizing this intuition of "distance", such that we could actually use it as a design measure? I think those metrics should converge on each other as you refine the shape of your program toward the Right Thing. Rephrased: Your module or scoping system serves you well to the extent that you can make hierarchies of modules and scope correspond to hierarchies in your mental model.