A separation logic for effect handlers

User-defined effects and effect handlers are advertised advocated as a relatively easy-to-understand modular approach to delimited control. They offer the ability of suspending resuming computation allow information be transmitted both ways between computation, which requests certain service, handler, provides this service. Yet, key question remains, day, largely unanswered: how does one modularly specify verify programs in presence user-defined primitive effects, such heap-allocated mutable state? We answer by presenting Separation Logic with built-in support for handlers, shallow deep. The specification program fragment includes protocol that describes may perform well replies it can expect receive. logic allows local reasoning via frame rule bind rule. It is based on Iris inherits all its advanced features, including higher-order functions, ghost state, invariants. illustrate power several case studies, (1) generic formulation control inversion, turns producer ``pushes'' elements towards consumer into from ``pull'' demand, (2) simple system cooperative concurrency, where threads execute concurrently, spawn new threads, communicate promises.