Re: How to include a file just once?

[James Bailey]

On 21.01.2010, at 18:47, Michael J. O'Donnell wrote:

> Is there a standard way to make sure that a file full of LilyPond  
> style
> definitions is included just once, no matter how many times it is  
> mentioned?
>
> I searched the Web site, mail archives, and /usr/shar/lilypond for
> "include once" and "include guard", to no avail. With the C
> preprocessor, there is a standard trick for setting and testing a
> variable to disable all but the first attempt to include a header  
> file.
> Some languages have an "include-once" command.
>
> I am putting together a large choral score from bookparts for each
> number in the work. I like to be able to produce either a single  
> number,
> or the whole score. The natural approach is to include style  
> definitions
> in each of the files that I might set, including the file to format  
> the
> whole score and the files to format individual numbers. Files to  
> format
> individual numbers also include the style definitions.
>
> I find that repeated inclusion of the same definitions leads  
> quickly to
> a segmentation fault.
>
> I can either add one more level of indirection, with one more file per
> number. Or, I can do some Scheme hacking, with a global variable to  
> set
> showing inclusion (tricky, because the variable needs to be testable
> reliably even when it has never been set explicitly).
>
> But, I'd prefer to use a well-known standard method, if it exists.
>
> Thanks,
>
> Mike O'Donnell

One solution might be to have either notes or layout definitions in a  
file, but not both. It quickly leads to large amounts of files, but  
you can have separate book files which create the actual parts, and  
not have multiple includes.