The barber or springfield

Barber.fsx

type Simpson = int

let [<Literal>] Homer : Simpson = 0
let [<Literal>] Bart  : Simpson = 1
let [<Literal>] Lisa  : Simpson = 2

// so heres the story:
// Bart shaves hisself,
// Lisa does not shave anyone
// and Homer shaves everyone who does not shave himself
let rec shaves b a =
    match a with
    | Bart  -> b = Bart
    | Lisa  -> false
    | Homer -> not (b |> shaves b)
    | _     -> false

// so let's see
let isShavedByHomer a =
    Homer |> shaves a 

isShavedByHomer Bart // nope
isShavedByHomer Lisa // err what?

isShavedByHomer Homer // DOH