Re: How parser stores Music objects in memory?

[Joao E. Pereira Jr]

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?

>> MY_MUSIC_SYNTAX calls are followed by Music::set_property() member
>> call, and them by Music::unprotect() member which return value is
>> assigned to grouping semantic value of action. AFAIK set_property
>> updates mutable_property_alist in the own object and unprotect
>> releases the object for GC when it becomes unused, even so I'm still
>> unable to tell how this object can be referred in future.
>
> 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? 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?

>> How parser handles this objects, I mean, where/how it stores Music
>> objects in memory?
>
> It is just an ordinary SCM object (a "smob") and managed by Guile's
> garbage collector.
>
> --
> David Kastrup
>
>
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-- 
João E. Pereira Jr