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Re: What is void music?

From: David Kastrup
Subject: Re: What is void music?
Date: Tue, 22 Aug 2017 15:44:39 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.0.50 (gnu/linux)

Dan Eble <address@hidden> writes:

> A. ly-syntax-constructors.scm has this.
>    (define-public (void-music)
>      (ly:set-origin! (make-music 'Music)))
> B. music-functions.scm has this:
>    ... (make-music 'Music 'void #t) ...
> In lily-library.scm, the function collect-music-aux has the comment "void 
> music is discarded”.  It seems to classify (B) as void music, but not (A).
> I stumbled at this when I tried to define a predicate for void music,
> used (B) as an example, and found that it didn’t catch ##{#}.  I’m not
> sure what to do.

What is it that you are trying to predicate?  The void flag is typically
set on music that is the result of an error.

> Are these different concepts that have been given the same name, or
> are they different valid representations of void music? ... or is the
> difference an error?

ly-syntax-constructors.scm is internal.  void-music is not

> C. There’s also \void, which appears to be related in name only.

*undefined* can be used in more places than it used to.

> I don’t know if renaming is appropriate, but in case it is, I offer these 
> suggestions:
>   A) “null” music
>   B) “annulled” music
>   C) no change

voided ?

At any rate, there is not a lot of consistency here.  This is mostly

There is

commit 7a57acf2755504cfb0813ca02662ad43e7456506
Author: Valentin Villenave <address@hidden>
Date:   Sun Oct 24 14:17:07 2010 +0200

    Revert make-void-music and \language functions.
    reverts commit 9e3d1968ffbbbdb60c06468dbdc30f6163dbe01b.
    reverts commit 1f84e8613c950b773562b95d87c5e051c8016650.
    reverts commit 02fe038744e634b42f1a3377c4f0dc3d25e80344.
    reverts commit 25a94417fb5484035bb816260a2168c17ae675ec.
    Better luck next time, I guess -- if any.

which apparently reverts an attempt to change it.  I don't know or at
least remember the history behind that.

David Kastrup

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