open System

type B() =
    member this.dString() = "B"

type T1() =
    inherit B()
    member this.dString() = "T1"

type T2() =
    inherit B()
    member this.dString() = "T2"

type PrinterOne(f:T1) =
    member this.GenericMethod() =
            printf "RESULT %A" (f.dString())

type PrinterG = | F of B
                | G of B with
    member self.GenericMethod() =
        match self with
        | F a ->
            printf "GENERIC %A" (a.dString())
        | G a ->
            printf "GENERIC %A" (a.dString())

let d1 = PrinterOne(T1())
d1.GenericMethod()

let d2 = F(T2())
d2.GenericMethod()