When I started learning F# I had a hard time grokking how and when to use a Discriminated Union (Sum type). I had experience in several paradigms and languages, but had never seen or used this data construct. In this article we'll start with an Enum and then work our way into an example use case with a Discriminated Union enum HttpMethod { Get, Post } An Enum is basically a constrained type where an instance of the enum must be one of the specified values. For an instance to be of the type HttpM[...]