Asynchronous Sessions with Implicit Functions and Messages

Session types are a well-established approach to ensuring protocol conformance and the absence of communication errors such as deadlocks in message passing systems. Haskell introduced implicit parameters, Scala popularised this feature and recently gave implicit types first-class status, yielding an expressive tool for handling context dependencies in a type-safe yet terse way. We ask: can type-safe implicit functions be generalised from Scala's sequential setting to message passing computation? We answer this question in the affirmative by presenting the first concurrent functional language with implicit message passing. The key idea is to generalise the concept of an implicit function to an implicit message, its concurrent analogue. Our language extends Gay and Vasconcelos's calculus of linear types for asynchronous sessions (LAST) with implicit functions and messages. We prove the resulting system sound by translation into LAST.