Lambda the Ultimate

Anders Heljsberg presented new asynchronous programming constructs for C# at PDC10. There is documentation, videos and a technology preview download.

When your user interface is unresponsive or your server doesn’t scale, chances are you need your code to be more asynchronous. With today’s .NET Framework and language features, though, that is easier said than done.
The Microsoft Visual Studio Async CTP proposes a new language feature in C# and VB, and a new framework pattern to go with it, that will make asynchronous programming similar to – and about as straightforward as –synchronous programming.

How is this related to F#'s asynchronous workflows, and monads in general?

We describe the asynchronous programming model in F#, and its applications to reactive, parallel and concurrent programming. The key feature combines a core language with a non-blocking modality to author lightweight asynchronous tasks, where the modality has control flow constructs that are syntactically a superset of the core language and are given an asynchronous semantic interpretation. This allows smooth transitions between synchronous and asynchronous code and eliminates callback-style treatments of inversion of control, without disturbing the foundation of CPU-intensive programming that allows F# to interoperate smoothly and compile efficiently.

What's the connection to Scala's delimited continuations by type directed CPS transform?

We describe the implementation of first-class polymorphic delimited continuations in the programming language Scala. We use Scala’s pluggable typing architecture to implement a simple type and effect system, which discriminates expressions with control effects from those without and accurately tracks answer type modification incurred by control effects. To tackle the problem of implementing first-class continuations under the adverse conditions brought upon by the Java VM, we employ a selective CPS transform, which is driven entirely by effect-annotated types and leaves pure code in direct style. Benchmarks indicate that this high-level approach performs competitively.