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.
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