Re: bar-line interface part 2/2: New bar line definition standard (issue 6498052)

[Marc Hohl]

Am 30.09.2012 11:02, schrieb address@hidden:
> [...]
> First, the define-public is asking for trouble. You are exposing an
> internal Scheme data structure to users and make it overwritable by the
> user. If the user follows this invitation, the effects will bleed over
> from session to session. Never do that.
Ok.
> Consider _everything_ written in a .scm file as readonly conceptually.
> For an alist, you might want to define a _function_ returning the
> initial list, and the accessors should not be modifying it destructively
> (adding to the front of an alist does not change the original alist).
>
> Then you assign this initial value to a session variable in something
> included in init.ly, like
> #(define bar-glyph-alist (initial-bar-glyph-alist))
Ok.
> Your functions working with bar-glyph-alist have to take the version of
> bar-glyph-alist defined in the parser module. That means that when you
> call them from .ly files, you'll likely need to pass bar-glyph-alist
> from the .ly file into your Scheme function. Or get them via
> ly:parser-lookup via the parser variable.
I am not sure whether I understand this completely, but I'll give
it a try.
> If you put a new bar line definition into a.ly, and when calling
> lilypond a.ly b.ly
> it is available in b.ly, then you have done something wrong.
I did this and can confirm that a bar line defined in a.ly *is*
available in b.ly.

So I have to replace all three public alists in bar-line.scm the way you
described it above.

[OT: it seems that I have a strong attraction to problems that look
not very difficult at first glance and turn out to involve *a lot of*
changes and obstacles until they get solved.
On the other hand, this is a *perfect* way to learn about the internals
of lilypond – in such situations where everything breaks, I remember
Jan working on GUB during Waltrop and his statement when the
compilation broke again: "That's nice." I admire such a serenity and
try to adopt it in situations where I am about to throw the computer
out of the window ;-) I am not in this state yet, but I am working on it...]

Regards,

Marc
> http://codereview.appspot.com/6498052/