25.11 Nulled subtrees and events

As mentioned above (see Nullability in the valuator), nulled subforests are, for evaluation purposes, pruned back to their topmost symbol. This is not the case for events. Events for every nulled symbol in the subforest will trigger, even if these symbols are pruned in the evaluation phase. More precisely, if

• X@j-j is a nulled symbol instance,
• X@j-j derives Y@j-j (in which case Y@j-j must also be a nulled symbol instance), and
• the event MARPA_EVENT_SYMBOL_NULLED for symbol Y is activated,

then a MARPA_EVENT_SYMBOL_NULLED for symbol Y will trigger at parse location j.