[Oberon] SystemV - Viewer Scroll

Andreas Pirklbauer andreas_pirklbauer at yahoo.com
Tue Mar 19 16:34:48 CET 2019

   > This discussion is interesting for a physicist. Time in physics theories
   > can equally well flow in either direction. The motion as a function of T
   > is equally good as the motion as a function of (-T). I would think that
   > the situation is the same with Text display. Scrolling up or down should
   > be equivalent. Why is the beginning of the Text any different from the end?
   > If you can count from the beginning, you can equally well count from the end.
   > If not then why not?

In principle scrolling of text should of course be "direction-symmetric", just like
the classical laws of physics are time-symmetric (replace T by -T).

However, the underlying access operations (Texts.Read and Files.Read) are not
direction-symmetric, and that is what complicates things a little bit (but not much).

(ps: as a fun exercise, you can in fact make Files.Read and Texts.Read totally direction-
symmetric by modifying the underlying modules Files and Texts - in such a world text
scrolling would indeed be completely direction-symmetric as well, taking either dY
or -dY. But this is quite involved, as it would require meddling with both the file
buffer mechanism in Files and the piece list in Texts.. it’s just not worth it).

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