https://fsharpforfunandprofit.com/posts/designing-with-types...

while visiting https://dotnetfiddle.net and typing the code samples in, experimenting with what manner of changes and additions to the code cause the compilation to fail, and considering how you would leverage those abilities in your everyday development work.

I think this would be even more powerful if you then come back and re-read some of the pro-Union comments in this very thread.