\version "2.16.1"

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%% generalized offsetter
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

#(define (pair-list? x)
  (and (pair? x)
       (every number-pair? x)))

#(define (offset-general arg offsets)
  (cond
    ((null? offsets) arg)
    ((number? arg) (+ arg offsets))
    ((number-pair? arg) (coord-translate arg offsets))
    ((pair-list? arg)
     (map
       (lambda (x y) (coord-translate x y))
       arg offsets))))

#(define ((offsetter property offsets) grob)
  (let* ((immutable (ly:grob-basic-properties grob))
         (target (assoc-get property (reverse immutable)))
         (vals
           (if (procedure? target)
               (if (procedure-name target) ; check for #<procedure #f (grob)>
                   (target grob)
                   '())
               target)))

    (if (or (number? vals)
            (number-pair? vals)
            (pair-list? vals))

        (let* ((orig (ly:grob-original grob))
               (siblings
                 (if (ly:spanner? grob)
                     (ly:spanner-broken-into orig)
                     '()))
               (total-found (length siblings)))

          (define (helper sibs offs)
            (if (pair? offs)
                (if (eq? (car sibs) grob)
                    (offset-general vals (car offs))
                    (helper (cdr sibs) (cdr offs)))
                vals))

          ;; standardize form of offsets
          (if (or (null? offsets)
                  (and (number? offsets) (number? vals))
                  (and (number-pair? offsets) (number-pair? vals))
                  (and (pair-list? offsets) (pair-list? vals)))
              (set! offsets (list offsets)))

          (if (>= total-found 2)
              (helper siblings offsets)
              (offset-general vals (car offsets))))

        vals)))

offset =
#(define-music-function (parser location name property offsets)
  (string? scheme? scheme?)
  (let* ((name (string-regexp-substitute " " "" name)) ; remove any spaces
         (name-components (string-split name #\.))
         (context-name "Voice")
         (grob-name #f))

    (if (> 2 (length name-components))
        (set! grob-name (car name-components))
        (begin
          (set! grob-name (cadr name-components))
          (set! context-name (car name-components))))
 #{
   \override $context-name . $grob-name $property =
     #(lambda (grob) ((offsetter property offsets) grob))
 #}))

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
staffUp = \change Staff = "upper"
staffDown = \change Staff = "lower"

soprano= \relative c'{
    \time 2/4 s2
    
    \once \offset Beam #'positions #'(1.75 . -1.5)
    % For broken beams, you would use something like the following:
    % \once \offset Beam #'positions #'((-1 . -2) (-3 . -2))
    
    %\override Beam #'positions = #'(1 . 0.7)   %can't adjust beam relative to upper staff centerline (desired)
    %\override Beam #'positions = #'(10.5 . 9.5) %values relative to lower staff centerline subject to between-staff distance
    \staffDown g8[ \staffUp e'd c]
}
bass = \relative c{ \clef bass s2 <e c>2}
    
\score{
      \new PianoStaff <<
            \new Staff = "upper" \soprano
            \new Staff = "lower" \bass
      >>
      \layout{}
}