polymor[hic decomposition

gistfile1.txt

type IFoo =
    abstract Do : unit -> unit

type Foo1() = 
    interface IFoo with
        member x.Do() = ()

type Foo2() = 
    interface IFoo with
        member x.Do() = ()

let list = 
    [
        Foo1() :> IFoo;
        Foo2() :> IFoo;
        Foo1() :> IFoo;
        Foo2() :> IFoo;
        Foo1() :> IFoo;
        Foo2() :> IFoo;
    ]

let result = Seq.groupBy (fun x -> x.GetType().FullName) list |> Seq.map snd