RE: Scheme help request: How can else of an if-statement be made to do nothing?

[John Schlomann]

Harm,

You used a function or macro called add-text. I can't seem to find it in any 
LilyPond or Guile manual. What is that?

John

> -----Original Message-----
> From: lilypond-user [mailto:lilypond-user-
> bounces+jschlomann=wideopenwest.com@gnu.org] On Behalf Of Thomas
> Morley
> Sent: Saturday, October 17, 2020 2:24 PM
> To: David Kastrup
> Cc: Jean Abou Samra; Matthew Fong; lilypond-user
> Subject: Re: Scheme help request: How can else of an if-statement be made
> to do nothing?
> 
> Am Sa., 17. Okt. 2020 um 20:33 Uhr schrieb David Kastrup <dak@gnu.org>:
> >
> > Thomas Morley <thomasmorley65@gmail.com> writes:
> >
> > > Am Sa., 17. Okt. 2020 um 19:39 Uhr schrieb Jean Abou Samra
> <jean@abou-samra.fr>:
> > >>
> > >> The point of interpret-markup is to turn a markup into a stencil, so I'd
> > >> use empty-stencil:
> > >>
> > >> \version "2.20.0"
> > >>
> > >> #(define-markup-command (print-if-defined layout props sym text)
> > >>                          (symbol? markup?)
> > >>    (if (defined? sym)
> > >>        (interpret-markup layout props
> > >>          #{ \markup \with-color #'(0.8 0.2 0.2) #text #})
> > >>        empty-stencil))
> > >>
> > >> symA = "Something"
> > >>
> > >> \markup {
> > >>    \print-if-defined #'symA "Text"
> > >>    \print-if-defined #'symB "More text"
> > >> }
> > >>
> > >
> > > An empty stencil will still be spaced (unless removed by other
> > > markup-commands).
> >
> > empty-stencil will typically not trigger additional spacing.  That's
> > typically what distinguishes it from point-stencil .
> >
> > --
> > David Kastrup
> 
> Well, I'd say it depends how that empty-stencil is consumed. See:
> 
> \markup
>   \box
>   { \stencil #point-stencil \stencil #empty-stencil \stencil #point-stencil }
> 
> Here I did something silly (of course there are warnings emitted) and
> the output _is_ affected.
> 
> Thus, the detailed use-case is important...
> 
> Cheers,
>   Harm