Dan J’s Website

Setting up Visual Studio Code for F#

• Cool: you can open a Terminal in VSCode with ^ + `
• Do I need to install an extension to use F#? Syntax colouring is built in, looks like
• Let’s try creating an FSX script file
  • Ok, I can do that, it has syntax highlighting, but I have no way to, you know, evaluate the scriptfile
  • Let’s see how you install F# in the modern .NET Core world…
  • I’m pretty sure I already have .NET Core installed via Homebrew
  • Yup, got the dotnet-sdk cask
• There’s the ionide-f# extension, but its website feels outdated, like it talks about needing Mono to get F#, which I’m pretty sure isn’t true. I want to do the most minimal and most up-to-date thing
• Ok, this Microsoft doc says “Ionide will generate .NET Framework F# projects, not dotnet core, which can have cross-platform compatibility issues. If you are running on Linux or OSX, a simpler way to get started is to use the command-line tools.”
  • That links here: https://docs.microsoft.com/en-us/dotnet/fsharp/get-started/get-started-command-line
  • Which talks about creating a solution and project, I just want to run a script
  • Good old searching for dev info on things that change rapidly: everything you find is out of date 🙄
• Ah, dotnet --help includes “Additional commands from bundled tools”, which includes fsi, but fsi is not a command on my path currently. So I have to figure out how to execute it… (I wonder if Homebrew Cask installed it, but only put dotnet in my path…)
• Ohhh… the first post in this thread inadvertently demonstrates that you use it like this: dotnet fsi 😏
• When I run it, this message appears:

> Failed to install ctrl-c handler - Ctrl-C handling will not be available. Error was:
        Could not load file or assembly 'Mono.Posix, Version=2.0.0.0, Culture=neutral, PublicKeyToken=0738eb9f132ed756'. The system cannot find the file specified.

• Nonetheless, if I write printfn "Hellow World!";;, it obediently prints it, and its evaluation that val it : unit = ()
• From here, we should be able to just provide the filename of an FSX file to FSI, and it’ll run it. Let’s try
• > dotnet fsi ~/dev/dotnet-projects/fsharp/test.fsx
• Despite that error message up there, hitting ^C did indeed terminate the interactive prompt
• Now let’s try that command above to run the script
• Yup, it prints Hello World! Success! 🤩
• Ah, from the FSharp tutorial I linked above, you can run commands from the interactive prompt by prefixing them with #, e.g. #quit quits the prompt
• Ok, cool: I can write scratch code in an FSX file and then run it at the built-in terminal. This will come in useful as I read the book version of FSharpForFunAndProfit

Intellisense

• It looks to me like this is what you need the Ionide extension for VSCode for. Let’s try installing it and see if it does anything to my FSX file
• Ionide-fsharp - “This extension is recommended based on files you recently opened”, I reckon that’s a good sign.
  • Its last update was six days ago, which is also a good sign
• Ah, I have a little button in the upper-right of the tab bar that lets me run the script or send to FSI. When I try to run script, it opens the terminal and says “fsharpi: command not found”, so evidently it’s trying to use some runner that I don’t have 🤔
• Not sure how to get it to show me Intellisense errors, either. Might only work on files inside the typical .NET Solution/Project structure?
• Annoying: There are a set of commands added to the VSCode command bar prefixed with F#:, but if you type F#: into the bar, it ignores the non-alphanumeric characters and finds every fucking command with an F in it, and of course the F#, perhaps because they’re newest, are all at the bottom of the list 🙄
• Intellisense is clearly not working, because I wrote the word “inference” in a comment, declared a value i, and when I typed i elsewhere (to assign the value as one of the values in a tuple), VSCode’s default Intellisense helpfully suggested “inference” instead of the, you know, actual symbol…
• Well, let’s try creating a project from the command bar and see what Ionide does with it
• It complains there’s no open folder. True! Let’s open ~/dev/dotnet-projects/fsharp
• I wonder if it can’t evaluate my file because of the missing fsharpi
• Ooookay: the New Project thingy asked for a folder name and a project name and then said it succeeded, but I don’t see a new folder or project anywhere that I’d expect…
• The F#: Get Help command does sweet fuck all
• Maybe I should restart Visual Studio?
• Nah that didn’t make a difference
  • This extension’s lack of feedback is frustrating. It just doesn’t work and doesn’t seem to indicate why
• This troubleshooting section has some things to try
  • this suggests I need to install mono…

Time Passes...

Getting F# Projects Working

• Get Started with F# in Visual Studio Code - Microsoft Docs looks like a promising walkthrough
• I already have Ionide installed in VSCode (see above), so let’s see if I can just create a project on the CLI and load it
• Cool, that’s working. I’ve got an Ionide icon in the sidebar now that shows me the solution explorer; looks like Intellisense works!
• Nice: the scripting example works, too. If I save a file as .fsx (I’m saving it in the project’s directory, I don’t know if this is required, or if it’ll parse any FSX file)
  • I just tested it: it parses an FSX on my Desktop just fine 👍🏼
• Sweet: I now have a programming environment I can use to learn more about F# and write some useful programs with it.