Availability:built-in
bee
on backtracking despite the fact that bee
is already retracted.85Example by
Jan Burse
:- dynamic insect/1. insect(ant). insect(bee). ?- ( retract(insect(I)), writeln(I), retract(insect(bee)), fail ; true ). ant ; bee.
If multiple threads start a retract on the same predicate at the same
time their notion of the entry generation is adjusted such that
they do not retract the same first clause. This implies that, if
multiple threads use once(retract(Term))
, no two threads
will retract the same clause. Note that on backtracking over retract/1,
multiple threads may retract the same clause as both threads respect the
logical update view.