The solution to this dilemma is to write one version of segment - pattern - p and segment-matcher, once and for all, but to have these functions refer to a table of pattern/action pairs. The table would say "if you see ?* in the pattern, then use the function segment-match," and so on. Then programmers who want to extend the matcher just add entries to the table, and it is trivial to merge different extensions

(unless of course two programmers have chosen the same symbol to mark different actions).