Abstract

Machine) is the most efficient sequential interpreter of Prolog programs. However, it gives a constraint of the garbage collection: the temporal order of the objects on the heap must be kept in order to be able to undo the changes on backtracking. Nowadays the actual requirements on a garbage collector include the incremental feature and the usability in virtual memory systems. W.J.Older and J.A.Rummel proposed in [Old92]an incremental garbage whose short collection phases are built into the code of the compiled Prolog program (WAM code). These short phases use a copying algorithm despite the fact that copying algorithm is not a sliding compactor. A choicepoint stack is used in WAM in order to permit bactracking. A choicepoint holds information required to return the computation to the state just before a non-deterministic call. For example, it stores pointers which show the end of the heap and environment stack before the call. The deleting of the unnecessary data (because of the fail...

Citations