Get a seq of all the cases of union type in F#

cases.fs

open Microsoft.FSharp.Reflection

let cases<'a> = seq {
    for case in FSharpType.GetUnionCases typeof<'a> do
        yield (FSharpValue.MakeUnion(case, [||]) :?> 'a)
}

example.fs

type Animal = Cat | Dog | Mouse | Pig | Chicken

let animals = cases<Animal>
animals |> Seq.iter (printfn "%A")