C# REPL outside Visual Studio

Question

F# has a REPL (read–eval–print loop) F# Interactive, C:\Program Files (x86)\Microsoft F#\v4.0\Fsi.exe.

I understand C# now has its own interactive REPL, as released with Roslyn. How do I open outside Visual Studio? Where is csi.exe?

Answer 1

C# Interactive window and csi.exe REPL were added to Visual Studio 2015 Update 1 (emphasis mine):

Introducing Interactive

The Interactive Window is back! The C# Interactive Window returns in Visual Studio 2015 Update 1 along with a couple other interactive treats:

• C# Interactive. The C# Interactive window is essentially a read-eval-print-loop (REPL) that allows you to play and explore with .NET technologies while taking advantage of editor features like IntelliSense, syntax-coloring, etc. Learn more about how to use C# Interactive on Channel 9 or by reading our beginner’s walkthrough.

• csi. If you don’t want to open Visual Studio to play around with C# or run a script file, you can access the interactive engine from the Developer Command Prompt. Type csi /path/myScript.csx to execute a script file or type simply csi to drop inside the command-line REPL.

• Scripting APIs. The Scripting APIs give you the ability to execute snippets of C# code in a host-created execution environment. You can learn more about how to create your own C# script engine by checking out our code samples.

See What’s New in Visual Studio 2015 Update 1 for .NET Managed Languages.

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https://www.visualstudio.com/en-us/news/vs2015-update1-vs.aspx

>csi
Microsoft (R) Visual C# Interactive Compiler version 1.1.0.51109
Copyright (C) Microsoft Corporation. All rights reserved.

Type "#help" for more information.
> #help
Keyboard shortcuts:
  Enter         If the current submission appears to be complete, evaluate it.  Otherwise, insert a new line.
  Escape        Clear the current submission.
  UpArrow       Replace the current submission with a previous submission.
  DownArrow     Replace the current submission with a subsequent submission (after having previously navigated backwards).
REPL commands:
  #help         Display help on available commands and key bindings.
Script directives:
  #r            Add a metadata reference to specified assembly and all its dependencies, e.g. #r "myLib.dll".
  #load         Load specified script file and execute it, e.g. #load "myScript.csx".
>
> Enumerable.Range(10)
(1,12): error CS7036: There is no argument given that corresponds to the required formal parameter 'count' of 'Enumerable.Range(int, int)'
> Enumerable.Range(1, 10)
RangeIterator { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }