Lazy Stream Programming in Prolog

Abstract

In recent years, stream processing has become a prominent approach for incrementally handling large amounts of data, with special support and libraries in many programming languages. Unfortunately, support in Prolog has so far been lacking and most existing approaches are ad-hoc. To remedy this situation, we present lazy stream generators as a unified Prolog interface for stateful computations on both finite and infinite sequences of data that are produced incrementally through I/O and/or algorithmically.We expose stream generators to the application programmer in two ways: 1) through an abstract sequence manipulation API, convenient for defining custom generators, and 2) as idiomatic lazy lists, compatible with many existing list predicates. We define an algebra of stream generator operations that extends Prolog via an embedded language interpreter, provides a compact notation for composing generators and supports moving between the two isomorphic representations.As a special instance, we introduce answer stream generators that encapsulate the work of coroutining first-class logic engines and support interoperation between forward recursive AND-streams and backtracking-generated OR-streams.

Lazy Stream Manipulation in Prolog via Backtracking: The Case of 2P-Kt

“…In our perspective, this work represents one further step towards the practical exploitation of LP -and, in particular, Prolog -as a general means for stream processing. Notably, our contribution presents some similarities with other works [15,14]. In particular, similarly to [15], we focus on letting Prolog manipulate streams of data; while, similarly to [14], we provide a mechanism to let logic solvers delegate computations to extenal entities.…”

“…In particular, similarly to [15], we focus on letting Prolog manipulate streams of data; while, similarly to [14], we provide a mechanism to let logic solvers delegate computations to extenal entities. However, differently from [15], we require no variation to the syntax, functioning, or libraries of Prolog; while, unlike [14], we focus on Prolog rather than ASP.…”

“…In this paper, we focus on the Prolog [10] programming language-arguably, the most popular LP language. Currently, Prolog can hardly be considered as a suitable stream-processing technology [15], as it provides minimal support for consuming both cold and hot streams. However, we believe that this should be reconsidered because Prolog already supports the lazy exploration of possibly infinite search spaces via backtracking.…”