Re: What is the significance of X in Lilypond?

[David Sumbler]

On Tue, 2020-08-04 at 08:21 -0600, Carl Sorensen wrote:
> 
> 
> On Tue, Aug 4, 2020 at 7:00 AM David Sumbler <david@aeolia.co.uk>
> wrote:
> > My latest Lilypond project had been compiling satisfactorily.  But
> > at a
> > certain point it began throwing out the following message:
> > 
> > %%%%%
> > Preprocessing graphical
> > objects.../usr/local/lilypond/usr/share/lilypond/current/ly/engrave
> > r-
> > init.ly:836:5: In procedure ly:stencil-extent in expression
> > (ly:stencil-extent (ly:note-head::print g) X):
> 
> This particular line is trying to find the X-extent (horizontal
> extent) of the note-head you are printing.
> 
> X and Y are defined as Scheme constants for the X (horizontal) and Y
> (vertical) directions.
> 
> One feature of Scheme is that you can redefine anything.  So you
> redefined X and it caused problems.
> 
> A general rule for lilypond is to avoid any variable names that are
> all uppercase.  In addition to X and Y, LEFT, CENTER, RIGHT, UP, and
> DOWN are all defined Scheme constants, and if you redefine them it
> will cause problems. 
> 
> HTH,
> 
> Carl

Thank you for that clear explanation.  I knew it must be something like
that, but couldn't guess what X was.

I had started off with lower-case Roman numerals, but that gives a
problem with 100 and 500, which are also note-names.  I suppose the
best solution is probably to use upper case C and D (and M, probably),
and lower case i, v, x and l, so that 1,444 would be MCDxliv.  That
doesn't look too bad, and should keep me, Lilypond and Scheme all
happy.

David