Optimisation of language-integrated queries by query unnesting

In this paper, we claim that moving of selected methods for automated optimisation elaborated for declarative query languages to the level of imperative programming languages is possible and desired. Our approach is based on the assumption that programmer is able distinguish whether a language-integrated query is intentionally used to introduce some side-effects or its sole purpose is to only query the data. We propose two optimisation procedures through query unnesting designed to avoid unnecessary multiple calculations in collection-processing constructs based on higher-order functions. We have implemented and verified this idea as a simple proof-of-concept LINQ optimiser library.