Stencils - first steps

[Andrew Bernard]

Trying to come to terms with lilypond Scheme, as a beginner, I am trying to add items to a notehead stencil, using a callback function.

My first attempt to simply get the stencil and return it does not succeed.

#(define expNoteHeadStencil

   (lambda (grob)

     (let* ((stil (ly:grob-property grob 'stencil)))

     stil)))

calling with:

  \override Staff.NoteHead.stencil = #expNoteHeadStencil

In general, how does one create a stencil for use with the stencil functions in Scheme? How can you make a stencil to be used as an argument to ly:stencil-add?

Somebody should write a book Lilypond Programming for Dummies. (I am serious).

Andrew