Jean Abou Samra <j...@abou-samra.fr> writes: > [Valentin] >> Hello Jean, hello David, hello Kieren, >> >> you should even be able to write (if sten (ly:stencil-extent sten)), >> as the stencil should always be a stencil or #f. > > > The two universally accepted values for any property > regardless of the predicate are #f and '(), so it > may still be '(), which is why checking with specific > predicates like this is often used in LilyPond's > source.
'() is a bit of an ugly cookie since it for some reason has been chosen to be the default for unset properties (seems like a Lisp rather than Scheme idea to me) but shouldn't be used by users for stuff not formally fitting the predicate. In my handwavy impression of trying to sort-of guess unwritten coding conventions. -- David Kastrup
