Memoized Pull-Tabbing for Functional Logic Programming

TL;DR

This paper introduces an improved pull-tabbing evaluation technique for functional logic programming that avoids efficiency issues caused by choice duplication, demonstrated through a Julia implementation.

Contribution

It proposes a refined pull-tabbing method that prevents choice duplication, maintaining the technique's flexibility and efficiency in functional logic languages.

Findings

The refined method reduces execution time compared to traditional pull-tabbing.

Implementation in Julia shows practical viability and performance benefits.

Maintains independence from search strategies while improving efficiency.

Abstract

Pull-tabbing is an evaluation technique for functional logic programs which computes all non-deterministic results in a single graph structure. Pull-tab steps are local graph transformations to move non-deterministic choices towards the root of an expression. Pull-tabbing is independent of a search strategy so that different strategies (depth-first, breadth-first, parallel) can be used to extract the results of a computation. It has been used to compile functional logic languages into imperative or purely functional target languages. Pull-tab steps might duplicate choices in case of shared subexpressions. This could result in a dramatic increase of execution time compared to a backtracking implementation. In this paper we propose a refinement which avoids this efficiency problem while keeping all the good properties of pull-tabbing. We evaluate a first implementation of this improved technique in the Julia programming language.