Asynchronous exceptions in Haskell

Asynchronous exceptions, such as timeouts, are important for robust, modular programs, but are extremely difficult to program with-- so much so that most programming lan-guages either heavily restrict hem or ban them altogether. We extend our earlier work, in which we added synchronous exceptions to Haskell, to support asynchronous exceptions too. Our design introduces scoped combinators for blocking and unblocking asynchronous interrupts, along with a some-what surprising semantics for operations that can suspend. Uniquely, we also give a formal semantics for our system. 1 Int roduct ion An important goal of language design is to support modu-larity. For concurrent languages, this goal means language support for localizing synchronization issues and support fo