[luatex] node missing

[Andreas Matthias]

Paul Isambert wrote:

> Andreas Matthias <andreas.matthias at gmail.com> a écrit:
>> 
>> Paul Isambert wrote:
>> 
>>> Andreas Matthias <andreas.matthias at gmail.com> a écrit:
>>>> 
>>>> In the following example I expected \mybox to contain `abc'
>>>> eventually. Instead it only contains `bc'. Why is the `a'
>>>> missing?
>>> 
>>> You must assign n1 to box.head, as in
>>> 
>>> [...]
>>>       n1.next = box.head
>>>       box.head = n1       
>>>       tail = node.slide(n1)
>>> [...]
>>> 
>>> otherwise the box still points to its former head as its first node
>>> (which has indeed n1 as its prev node, but it is ignored because scanning
>>> begins at the former head).
>> 
>> 
>> Hmm. I see it's working now but I still don't understand why.
>> 
>> Function foo creates and returns an hlist `h' and I thought this
>> hlist would be assigned to mybox with
>> 
>>    tex.setbox(mybox, foo(tex.box.mybox))
>> 
>> Hlist `h' does not contain the original box but the interior of
>> the box, does it? Then why do I have to set box.head?
> 
> Sorry, I didn't pay enough attention. I thought it was the usual error
> (forgetting to reassign to a list's head being quite common).
> 
> Actually, 
> 
>     tex.setbox(mybox, foo(tex.box.mybox))
> 
> doesn't mean anything, it should be:
> 
>     tex.setbox("mybox", foo(tex.box.mybox))

Yes, I see. That was nonsense.

Are there any use cases of

   tex.setbox(nil, ...)

at all? Or wouldn't a warning be more appropriate than
silently accepting nil?

> Consequently:
> 
>       n1.next = box.head
> 
> should be:
> 
>       n1.next = node.copy_list(box.head)
> 
> Otherwise LuaTeX will be stuck in a loop (I have no time to investigate
> why, but it does so).

What a nice loop! My notebook completely stalled!


Ciao
Andreas