Scheme: get current beam-thickness

[David Stephen Grant]

I'm trying to create a custom flag stencil, and would like to get the
current _beam_ thickness. As a first step, in the following example I would
expect 0.5, then 1, to be printed to the console. Is there a way of doing
this?

Thanks,
David

\version "2.19.83"
#(define (my-flag)
  (lambda (grob)
    (format #t "~a"
      ;;; GET THE CURRENT BEAM-THICKNESS
      )
    empty-stencil))
{
  \override Flag.stencil = #(my-flag)
  \override Beam.beam-thickness = #0.5
  c'8 r8
  \override Beam.beam-thickness = #1.0
  c'8 r8
}