- Derived classes should only have a public constructor.
- The state of an iterator would be the intersection of the particular music
- construct with one point in musical time.
- */
+
+ ok () -- events left ?
+
+ pending_mom () -- time tag of the next event to be processed.
+ PRECONDITION: this->ok () holds.
+
+ process (M) -- process all at M (Precondition: no events exist
+ before M, this->ok () holds). Side-effects:
+
+ * This removes all events at M from the pending queue.
+
+ * Typically this reports the music to an interpretation context,
+ thus changing the state of the interpretation context.
+
+ get_music (M) -- return all events starting at M (pre: no events
+ before M). No side-effects
+
+ skip (M) -- remove all events starting before M (leave the ones that
+ start M). no side-effects on interpretation context
+
+
+ TODO:
+
+ merge pending_moment and process?
+
+*/