Let define-session-public place variables natively into parser

Let define-session-public place variables natively into parser

Putting them as native variables in the parser module (rather than
using export/import) makes `set!' and `define' equivalent rather than
having `define' create a shadowing definition of the session variable.
That is important in order to avoid the values of the variable
diverging between parser module and `lily'.

[Carl, 2016-05-27 04:23:29]

Looks very nice to me.  I couldn't have done it, but I love how it works.

Thanks,

Carl

[dak, 2016-05-27 06:03:44]

On 2016/05/27 04:23:29, Carl wrote:
> Looks very nice to me.  I couldn't have done it, but I love how it works.

Can you elaborate on the "couldn't have done it" part?  define-session-public
copies some ugly code (concerning undead structures or something) from
define-session.  Is it that, or the heavily underdocumented module system of
Guile that's involved here?  Because I have a patch reorganizing the session
stuff in limbo that would remove/replace the undead machinery with something
saner.  Possibly giving fewer useful diagnostics, but we haven't had any
_useful_ hint from that area for years.

We certainly want to minimize "couldn't have done it" code since we don't want
to depend on particular persons for the continued well-being of LilyPond.

[Carl, 2016-05-27 15:05:41]

On 2016/05/27 06:03:44, dak wrote:
> On 2016/05/27 04:23:29, Carl wrote:
> > Looks very nice to me.  I couldn't have done it, but I love how it works.
> 
> Can you elaborate on the "couldn't have done it" part?  define-session-public
> copies some ugly code (concerning undead structures or something) from
> define-session.  Is it that, or the heavily underdocumented module system of
> Guile that's involved here?  Because I have a patch reorganizing the session
> stuff in limbo that would remove/replace the undead machinery with something
> saner.  Possibly giving fewer useful diagnostics, but we haven't had any
> _useful_ hint from that area for years.
> 

It's the module system of Guile.  I have no idea how the module system works. 
I'm vaguely aware that there are modules, and that variables are scoped locally
to the modules, but that's about it.

To be fair, I haven't spent any time digging in to that aspect of LilyPond.  I
assume that if I dug into it I could learn it, but that's beyond my current
understanding.

Thanks,

Carl