First-class names for effect handlers

Algebraic effects and handlers are a promising technique for incorporating composable computational into functional programming languages. Effect enable concisely with different effects, but they do not offer convenient way to program instances of the same effect. As solution this inconvenience, previous studies have introduced _named effect handlers_, which allow programmer distinguish among instances. However, existing formalizations named both involved restrictive, as employ non-standard mechanisms prevent escaping handler names. In paper, we propose simple flexible design handlers. Specifically, treat names first-class values, their while staying within ordinary λ-calculus. Such is enabled by combining _scoped effects_, novel variation that maintain scope via rank-2 polymorphism. We formalize two combinations scoped implement them in Koka language. also present practical applications handlers, including neural network unification algorithm.