Implementing backjumping by means of exception handling

TL;DR

This paper explores implementing backjumping in Prolog using exception handling, revealing limitations and proposing solutions for specific cases, and analyzing the semantics with coroutining.

Contribution

It demonstrates the impossibility of general backjumping via exceptions in Prolog and offers two specialized solutions with detailed semantic analysis.

Findings

Backjumping cannot be generally implemented with exceptions in Prolog.

Two solutions are proposed: one for binary programs, another restricting backjump targets.

Discussion includes semantics with coroutining and database use.

Abstract

We discuss how to implement backjumping (or intelligent backtracking) in Prolog by using the built-ins throw/1 and catch/3. We show that it is impossible in a general case, contrary to a claim that ``backjumping is exception handling". We provide two solutions. One works for binary programs; in a general case it imposes a restriction on where backjumping may originate. The other restricts the class of backjump targets. We also discuss implementing backjumping by using backtracking and the Prolog database. Additionally, we explain the semantics of Prolog exception handling in the presence of coroutining.