Domain Specific Languages (DSL) are designed to be syntactically and semantically easier to use than general-purpose languages performing the same task. This is generally achieved by tailoring programming notions and constructs to the domain tasks at hand. Yet there are examples of domain specific problems that demand elaborate constructs (for e.g. aspects in Aspect DSLs) which need to be carefully introduced as to avoid complicating the language. We present such an example in Pharo for the epidemiological language KENDRICK. KENDRICK simplifies the programming of epidemiological simulations by decomposing highly-coupled monolithic models into modular concerns. This decomposition though, is based on a mathematical model that introduces non-trivial composition semantics into the language that need to be carefully integrated. In this work, we address this problem by extending KENDRICK's DSL with explicit composition semantics, entities and operators.