A first thing to learn in F# for a C# developer.

I will write about a trivial and obvious thing, but I still remember that it wasn’t when I was starting to learn F# and FP a few years ago. And when I finally got it, pieces of the puzzle just fell into place.

Why no circular data in pure FP?

A friend of mine started to read a book about F# after I told him maybe 1000 times how great functional programming is. He is experienced in C# and Java which arguably makes it harder (and definitely more annoying) to learn FP than if you are a beginner.

Clarification: F# is a mixed paradigm language but he chose it as a «gateway drug» and learns it from pure-ish FP perspective.

One of the things that pissed him off was that F# enforces to write code in compilation order (code ordering can be  much more relaxed since F# 4.0 by the way) and hence make it hard to create circular references.