type Shape() = class end

​

type Circle() = inherit Shape()

type Square() = inherit Shape()

​

type IGeometry<'foo when 'foo :> Shape> = interface end

​

module test =

​

​

    let useAny(baz: IGeometry<'Shape>) = match baz with

                                    | :? IGeometry<Square> -> ()// ...

                                    | :? IGeometry<Circle> -> ()//...

                                    | _ -> failwith "Not a valid shape yo"

    let useCircle(bar: IGeometry<Circle>) = useAny bar

​