in a scheme-engraver I want to get the stem-direction in the
acknowledger-slot. When I use ly:stem::calc-direction the calculated
direction is not always the visible one, when autobeaming is in effect.
A manual beam crashes lily.
So my question is: How can I retrieve the actual/current stem direction?
%%%%% snip %%%%%
#(define-public (stem-direction-engraver context)
; store stem direction
((stem-interface engraver grob source-engraver)
; this function crashes, if a beam starts
(ly:message "stem info ~A" (ly:stem::calc-direction grob))