One of the great new F# tools in .NET Core 3 Preview 3 is F# interactive as pure .NET Core application.

To use dotnet fsi in your Visual Studio Code with the Ionide F# IDE plugin instead of the fsharpi binary, add the following to your user settings.json:

"FSharp.fsacRuntime": "netcore",
"FSharp.fsiFilePath": "/usr/local/share/dotnet/dotnet",
"FSharp.fsiExtraParameters": ["fsi"]

Remember to replace fsiFilePath with wherever your .NET Core 3 dotnet binary is installed. (On mac and Linux, do which dotnet, on Windows where dotnet to find out.)

Besides the new colorization in dotnet fsi, this was useful to me to try out new F# 4.6 features interactively, such as the anonymous records, as the mono installation on this mac is still at 4.1.

The screenshot below shows the new dotnet fsi in action in Visual Studio Code:

vscode sending a line of code to dotnet fsi
Sending a line with an anonymous record example to F# 4.6 via dotnet fsi.