A Reference GLL Implementation

The Generalised-LL (GLL) context-free parsing algorithmwas introduced at the 2009 LDTA workshop, and since then aseries of variant algorithms and implementations have beendescribed. There is a wide variety of optimisations that maybe applied to GLL, some of which were already present inthe originally published form.This paper presents a reference GLL implementation shornof all optimisations as a common baseline for the real-worldcomparison of performance across GLL variants. This baselineversion has particular value for non-specialists, sinceits simple form may be straightforwardly encoded in theimplementer’s preferred programming language.We also describe our approach to low level memory managementof GLL internal data structures. Our evaluation onlarge inputs shows a factor 3–4 speedup over a naïve implementationusing the standard Java APIs and a factor 4–5reduction in heap requirements. We conclude with noteson some algorithm-level optimisations that may be appliedindependently of the internal data representation