Because ensembles and swarms occur everywhere in nature, in social and in technical contexts, their modeling and programming is one of the challenges of modern software systems engineering. While it is well-known how self-adaptive or autonomic systems can be designed advantageously (Kounev et al., 2017), this often requires the engineering of new software languages with a tremendous development effort. This paper presents a novel context-role-adaptive approach for modeling and programming of ensembles and swarms that relies on a small library in Julia (1300 SLOC), exploiting its facilities for metaprogramming, multiple dispatch, and equational modeling. We demonstrate the validity of the approach with a tutorial on two scenarios from the technical and natural domain in which ensembles are represented by (dynamic) contexts. RailCabs are shuttle-based autonomous trains, self-forming ensembles, represented as contexts that re-group during their travels. Bird swarms show specific formations, represented as contexts to save energy and to prevent attackers. In the latter case study, we show how to model the dynamic behavior of the birds with an equational modeling library in Julia. Therefore, the paper contributes a new library-based approach to Context-Role-oriented Equational Modeling of Ensembles (CREME).