Disjunctive Delimited Control

TL;DR

This paper introduces a novel disjunctive delimited control interface for Prolog that fully captures its non-deterministic nature, enabling advanced language features at the library level.

Contribution

It presents a new control mechanism that extends Prolog's capabilities by managing non-deterministic control flow, unlike previous formulations.

Findings

Enables implementation of findall, cut, and branch-and-bound at the library level.

Supports probabilistic programming within Prolog.

Provides a conservative extension via a meta-interpreter.

Abstract

Delimited control is a powerful mechanism for programming language extension which has been recently proposed for Prolog (and implemented in SWI-Prolog). By manipulating the control flow of a program from inside the language, it enables the implementation of powerful features, such as tabling, without modifying the internals of the Prolog engine. However, its current formulation is inadequate: it does not capture Prolog's unique non-deterministic nature which allows multiple ways to satisfy a goal. This paper fully embraces Prolog's non-determinism with a novel interface for disjunctive delimited control, which gives the programmer not only control over the sequential (conjunctive) control flow, but also over the non-deterministic control flow. We provide a meta-interpreter that conservatively extends Prolog with delimited control and show that it enables a range of typical Prolog features and extensions, now at the library level: findall, cut, branch-and-bound optimisation, probabilistic programming, . . . This paper is under consideration for publication in Theory and Practice of Logic Programming (TPLP).