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Anders Hejlsberg's C# 4.0 REPL
Is there a native window/extension in VS2010 where you can write one-liners and see the result( like the ‘Immediate Window’, witch, as far as I know, is only usable in Debug mode).
I’m not interested in external tools like Linq Pad or SnippetCompiler
With Roslyn, Visual Studio will get a built in interactive window:
http://blog.filipekberg.se/2011/11/14/using-the-c-interactive-window-that-comes-with-roslyn/
Unfortunately, it is still only at CTP status.