R1D23 Reverse Polish Hello World
I took a brief break from C# and cracked open a book I got a few months ago about the F# programming language. Functional programming is making a comeback it seems. I’ve done some work in Clojure and Lisp in the last few years. In addition I heard Javascript referred to as “Lisp in C’s Clothing” so that might count as well.
If JS is Lisp in C’s Clothing, I have no idea what clothing F# is wearing.
Rather than the traditional “Hello World” the first bits of code that we wrote was an implementation of a reverse polish notation calculator program.

The code for the function itself reminds me of writing grammars for ANTRL. I have no idea what “|” “|>” or “::” are doing in this context, but I can’t wait to find out. I was starting to get discouraged, but then following this code example the author reassures us.
“Don’t be discouraged if the RPN calculator code doesn’t make much sense right now; that’s the point! ”I am excited that I got all of this working out of the box on my Macbook. F# comes baked into the latest version of the dotnet core SDK. You can start a new F# project with the following incantation:Excerpt From: Dave Fancher. “The Book of F#: Breaking Free with Managed Functional Programming.” iBooks.
dotnet new console -lang F# -n MyFirstFSharpProject
You can run it with:
dotnet run
Like any good Lisp, F# comes with a built in REPL. It seems you need to install mono in order to get this to work. I was able to do it with homebrew.
brew install mono
Then you can fire up an F# repl with
fsharpi
You can test it out and make sure it works with a simple example.
> let greeting = "Hello from the F# REPL!" - greeting;; // output should be val greeting : string = "Hello from the F# REPL!" val it : string = "Hello from the F# REPL!"
I’m looking forward to learning a bit more F#. It is one of the out of the box supported languages on Azure Notebooks.
Thank you for reading! Share your thoughts with me on bluesky, mastodon, or via email.
Check out some more stuff to read down below.
Most popular posts this month
- 2024
- Reinstalling Windows at 1am
- SQLite DB Migrations with PRAGMA user_version
- My Custom Miniflux CSS Theme
- How to Disable Wayland in Debian Testing
Recent Favorite Blog Posts
This is a collection of the last 8 posts that I bookmarked.
- The AGI economy is coming faster than you think from Freethink
- Rolling the ladder up behind us from Xe Iaso's blog
- In Praise of “Normal” Engineers from charity.wtf
- Reports of Bluesky's death have been greatly exaggerated from The Torment Nexus
- What Would a Kubernetes 2.0 Look Like from matduggan.com
- We Can Just Measure Things from Armin Ronacher's Thoughts and Writings
- workflows for ai coding from /* 🤖🛠️ */
- Reinvent the Wheel from Matthias Endler
Articles from blogs I follow around the net
in the heat of the summer better call out a plumber
Back in the old days, the good old days, when it was generally accepted that Fascism and Nazis were bad, bloggers would write these posts that were sort of recaps […]
via WIL WHEATON dot NET June 20, 2025Just one more Patreon indignity
I was today years old when I learned that Patreon offers no mechanism to download all of your own posts from your "creator" account. Because fuck you that's why. Confirmed with "support" [sic] who sent me a response with the level of ov…
via jwz June 20, 2025Pluralistic: Oregon bans the corporate practice of medicine (20 Jun 2025)
Today's links Oregon bans the corporate practice of medicine: Karma for Unitedhealthcare, Part II. Hey look at this: Delights to delectate. Object permanence: 2015, 2020 Upcoming appearances: Where to find me. Recent appearances: Where I've been. …
via Pluralistic: Daily links from Cory Doctorow June 20, 2025Generated by openring