Minimal but General

Koka has a small core set of orthogonal, well-studied language features – but each of these is as general and composable as possible, such that we do not need further “special” extensions. Core features include first-class functions, a higher-rank impredicative polymorphic type- and effect system, algebraic data types, and effect handlers. 

Koka - A Functional Language with Effect Types and Handlers