Algebraic Effects Meet Hoare Logic in Cubical Agda

This paper presents a novel formalisation of algebraic effects with equations in Cubical Agda. Unlike previous work in the literature that employed setoids to deal with equations, the library presented here uses quotient types to faithfully encode the type of terms quotiented by laws. Apart from tools for equational reasoning, the library also provides an effect-generic Hoare logic for algebraic effects, which enables reasoning about effectful programs in terms of their pre- and post- conditions. A particularly novel aspect is that equational reasoning and Hoare-style reasoning are related by an elimination principle of Hoare logic.