Multiway merge with constant delay in Concurrent Prolog

Multiway dynamic mergers with constant delay are an essential component of a parallel logic programming language. Previous attempts to defined efficient mergers have required complex optimising compilers and run-time support. This paper proposes a simple technique to implement mergers efficiently. The technique requires an additional data type and the definition of an operation on it. The operation allows multiple processes to access a stream without incurring the cost of searching for the end of stream. It is specified in Concurrent Prolog and is used to define multiple assignment variables using a monitor. The technique forms the basis for stream merging in Logix, a practical programming environment written in Flat Concurrent Prolog.