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I'm trying to use Scala (2.9.0) continuations to build a seemingly blocking API, but that actually is asynchronous. Suppose that you would like to write something like: if(ask("Continue?")) //Prompts Yes/No name = input("Enter your name") Where ask returns a boolean if the user pressed yes, and input asks for a value. Picture this being called from a web server, where ask and input do not block any threads, they just store a continuation in a Map (or the session, doesn't matter much) before displaying the page with the prompt (releasing most resources). And when a response get's back, it looks-up the continuation in the Map and resumes the code. The problem so far is that I cannot seem to be able to find a suitable way to define ask and input to use continuations without passing the calling context's return type as a parameter. The closest I got is doing something like: #!/bin/sh exec scala -P:continuations:enable -deprecation "$0" "$@" !# import util.continuations._ //Api code def display[T](prompt: String) = shift { cont: (Unit => T) => { println(prompt) cont() } } //Client code def foo() : Int = reset { display[Int]("foo!") // <-- how do I get rid of the type annotation? 5 } def bar() : Unit = reset { display[Unit]("bar!") } println(foo()) bar() I really would like to get rid of the type annotation on calls to display . Does anyone know of a way of achieving this? I don't care if the API definition gets uglier, as long as the client code gets simpler. Thanks!

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