eliminating array bound checking in F#

gistfile1.fs

module ElimArrayBoundCheck =
  type BIndex<'Tag>(idx) =
    member this.Idx = idx
  type BArray<'Tag, 'T>(arr : 'T[]) =
    member this.lookup(bidx : BIndex<'Tag>) = arr.[bidx.Idx]

  type C<'T, 'R> = interface
    abstract s<'Tag> : BIndex<'Tag> * BArray<'Tag, 'T> -> 'R
    abstract f : 'R
  end

  let check (arr : 'T[]) (idx : int) (c : C<'T, 'Result>) =
    c.f(BIndex(idx), BArray(arr))

open ElimArrayBoundCheck

let main _ =
  check [| 1; 2; 3 |] 1 { new C.C<_, _> with
   member this.f(bidx1, barr1) =
    check [| 1; 2; 3 |] 1 { new C.C<_, _> with
     member this.f(bidx2, barr2) =
       barr1.lookup(bidx1) |> ignore
       barr2.lookup(bidx2) |> ignore
       //barr2.lookup(bidx1) |> ignore
       //barr1.lookup(bidx2) |> ignore
    }
  }

  0