R1D23 Reverse Polish Hello World

| programming | dotnet |

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.

Reverse Polish Notation Calculator in F#

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! ”

Excerpt From: Dave Fancher. “The Book of F#: Breaking Free with Managed Functional Programming.” iBooks.

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:

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

Recent Favorite Blog Posts

This is a collection of the last 8 posts that I bookmarked.

Articles from blogs I follow around the net

Give a Problem. Grow a Programmer.

In 2009, I kicked off my senior year in college with a class that ultimately changed the way I thought about my degree—and my future.

via flower.codes September 15, 2025

Yala stablecoin depegs after theft

The YU bitcoin-backed stablecoin list its intended dollar peg after what they described as "an attempted attack", later writing that there was an "unauthorized transfer of funds". Although they initially wrote that &#…

via Web3 is Going Just Great September 15, 2025

How big a solar battery do I need to store *all* my home's electricity?

I have a modest set of solar panels on an entirely ordinary house in suburban London. On average they generate about 3,800kWh per year. We also use about 3,800kWh of electricity each year. Obviously, we can't use all the power produced over summer an…

via Terence Eden’s Blog September 15, 2025

Generated by openring