[lltx] luatexbase.is_in_callback

Arno Trautmann Arno.Trautmann at gmx.de
Thu Jul 21 14:11:17 CEST 2011

Hi all,

I'd like to use the post_linebreak_filter to manipulate the node list, 
but only if a macro appears in that given paragraph. The straightforward 
way would be to let the macro register the function; however, using 
luatexbase.add_to_callback then gives an error if the macro is called 
twice. (which is allowed in the code)
Now, I could change the macro not to register anymore once called and 
set it back at the beginning of the next paragraph, but a much nicer way 
would be to have a function that checks if a function is already 
registered and does not throw an error.
In the end, what I'm asking for are two functions like
returning true or false, actually executing this code from the current 

if priority_in_callback(name, description) then
err("function ’%s’ already registered\nin callback ’%s’",
description, name)



also returning true or false and registering the function if it is not 

Is it possible to add this to luatexbase? It would be a very nice 
feature, but I don't know if many people would really need it …


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