Re: How parser stores Music objects in memory?

[David Kastrup]

"Joao E. Pereira Jr" <address@hidden> writes:

> On Sun, Jan 13, 2013 at 9:35 AM, David Kastrup <address@hidden> wrote:
>> "Joao E. Pereira Jr" <address@hidden> writes:
>>
>>> Many of the tokens parser reads ask for Music object creation so it
>>> calls MY_MUSIC_SYNTAX macro, as this object represents music content
>>> and layout even a one note ly file can lead to a considerable number
>>> of Music objects, so I deduce it plays an importante role in
>>> architecture. A lot of Music objects are created, but is not clear how
>>> they are stored in memory, or which data structure is used to handle
>>> them.
>>
>> They are of type ly:music?, check out lily/include/music.hh for their
>> structure.
>>
>
> Suppose I have the following ly code { c d e }, I think that in
> parsing 3 objects of ly:music? type will be produced and I'm wondering
> where this 3 objects would be put into: an array, a vector, a list?

A list, stored in the 'elements property of another Music structure of
type SequentialMusic.

>> MY_MUSIC_SYNTAX creates protected Music data which will not get
>> garbage collected because of an artificial extra reference to it.
>> After calling unprotect, this reference is gone, and the garbage
>> collector will collect the Scheme object once it can no longer detect
>> any _other_ reference to its SCM descriptor, whether on the stack, or
>> inside of some other SCM object reachable from the stack or otherwise
>> protected.
>>
>
> In C++ and Scheme terms of code, how can i use this artificial extra
> reference?

Not at all.  It is just internal to the garbage collector.  You can get
your own SCM reference at any time by calling ->self_scm () on the Music
pointer, or by calling ->unprotect () (which can only be called once) on
the Music pointer.  Having a Music pointer somewhere does not help
against garbage protection.  Having an SCM reference on the stack or in
some Scheme structure known to the garbage collector does.

> I'm trying to understand the flow of execution and how data is
> organized and passed through compiler stages. In the iteration (I
> didn't read iteration code yet) this Music objects should be
> referenced in some way. Do you have some advice to clear this up?

I don't understand your question.

-- 
David Kastrup