Back at the PDC in 2008, in the C# futures talk by Anders Hejlsberg he talked about rewriting the C# compiler and providing a "compiler as a service" I certainly got the impression at the time that they were targeting the C# 4.0 timeframe for this....
Well, does anyone know what the state of this is? it doesn't seem to be there in the CTP and there is almost no information on the WEB apart from links to the 2008 PDC session video (roughly an hour in).
Has this initiative gone dark?
Certainly not C# 4.0. We are just finishing up the last few bug fixes for C# 4.0.
This direction for the toolset is the long term plan, and might never come to fruition. And I don't discuss schedules for unannounced, hypothetical future features.
UPDATE: October 2011
We have just shipped a preview release of "compiler as a service" aka the "Roslyn" project.
We are still not announcing the final ship vehicle; it will be post Visual Studio 11.
It's already available in Mono for quite some time.
It has been released CTP version in the name of Roslyn. You can check it at RosLyn
As of today (19 October 2011), there is a CTP of Roslyn available for download at http://msdn.microsoft.com/en-us/roslyn.
The CTP installs on top of Visual Studio 2010 SP1.
I'm pretty sure I heard rumours of this being a "between 4.0 and 5.0" item now (a separate library, like ASP.NET MVC)... but I can't remember where I heard that. I certainly wouldn't expect it in 4.0 at this point. Frankly I don't even really know what the phrase means exactly - it could cover a whole range of features.
来源：https://stackoverflow.com/questions/2210734/what-is-the-state-of-the-c-compiler-as-a-service