THE PANDORA DEADLOCK HANDLER META-LEVEL RELATION

Pandora was first introduced in [11 as a new parallel logic programming language which combines don't-know non-determinism and stream and-parallelism in a unified and efficient manner. In this paper, we present the Pandora deadlock handler relation whose input argument is a list of meta-level representations of suspended goals. One way of utilizing the deadlock handler relation is in implementing (application-dependent) heuristic search. More generally, the deadlock handler relation can be used to manipulate suspended goals in a flexible manner; redundant goals can be removed, new goals can be added, and a group of goals can be replaced by a simpler group. We illustrate the use of the deadlock handler relation by various application programs and outline the features of the Pandora abstract machine which are required to support its functionality.