How can I avoid repetition in declaring similar types?

Question

I have the following code:

type CapturablePieces = Pawn | Knight | Bishop | Rook | Queen

I can define another type as follows:

type Pieces = Pawn | Knight | Bishop | Rook | Queen | King

However, there is obviously a lot of code repetition here. Is there a way to avoid this by incorporating CapturablePieces into the definition of Pieces?

Answer 1

If you don't need CapturablePieces to be separable type, just some subset of particular cases, maybe it can be implemented as member? I can think of two ways:

a) Collection of capturable pieces in static member:

type Pieces = Pawn | Knight | Bishop | Rook | Queen | King
    static member Capturable = [Pawn; Knight; Bishop; Rook; Queen]

b) Boolean member:

type Pieces = Pawn | Knight | Bishop | Rook | Queen | King
    member x.IsCapturable = match x with King -> false | _ -> true