This isn't really a REPL, though. It's missing the L. :-) Not evaluating each line as it comes makes it less fun to use.

With some obvious caveats, I'm a big fan of the csharp REPL provided by Mono: http://www.mono-project.com/CsharpRepl

Yeah, that will be too costly because it would have to make a server call pretty quickly to confirm that the code is complete. (The Roslyn desktop C# Interactive can do this because it's right on the desktop)

You can press Ctrl-Enter to send complete code, if you wish to send submissions faster.

Yeah, I understand. My expectations were just set a bit higher since you called it a REPL. Realistically, something like this fills a different use case anyway. When I want a REPL, I want to run it locally.

Not quite REPL (not sure C# is a great fit for REPL) but I've found LINQPad very useful for trying out code snippets locally. https://www.linqpad.net

LINQPad is one of the best tools I've ever used. I can't recommend it enough for anybody who wants a C# or F# scratchpad, or wants to quickly query a database.

I've written a blog post on Getting Started at http://www.ahuwanya.net/blog/post/introducing-csharp-pad

Wow, I was just looking for this a couple of days back!

Seems interesting but I got a 'Server Error: timeout' when trying to run a simple string.Format(). Bookmarked to try later!

There's a lot of Traffic on the server at the moment. Do try again later.

Seeing the same for a Hello World.

compile roslyn to js. Don't really need server here do you?

I didn't know that was possible. Even if you can compile Roslyn to JS to run on the client, you still need to compile most parts of the BCL as well, or else you still need to make a server call.

Sure. You may try compile IL to js http://jsil.org/

Is this using ScriptCS?

No, it's using Roslyn directly.

Smart, every time I see one of these I worry that someone malicious will attempt to delete the server's Windows folder.

Roslyn doesn't prevent you from doing that though. You still need to validate, filter and run your code in a sandbox.

Immediate window?

It's the web version of the Interactive window bundled with Roslyn.