[luatex] multiple callbacks

Hans Hagen pragma at wxs.nl
Wed Jan 14 00:21:23 CET 2009

Karl Berry wrote:
> Excuse me for coming in late, and with such an obvious comment, but how
> about handling such callback in lua a la hooks in Emacs?  The hook
> author can decide whether they want to ask that it be at the front of
> the list, the back of the list, or (default) don't care.  Of course
> there are no guarantees due to multiple packages requesting the same
> thing, but at least the basic options would be provided.

that's an example of a an implementation; in principle one can build all 
kind of handlers in lua and then hook the manager in the callback

function package_xyz_handler()
   -- this function manages the list of callbacks of pre-linebreak_filter

callback.register('pre_linebreak_filter', package_xyz_handler)

(i posted an example of such a handler and of course one can extend it 
with more advanced management)

however, the main problem is not such management but what exactly 
happens in the individual actions; this is really up to the macro 
package (writers) to keep some control over, that is: there are 
manipulations that can spoil later manipulations

there are just too many possibilities (this is comparable to dealign 
with fonts or encodings or auxiliary files in macro packages .. each has 
its own way of doing things); implementing a manager is rather simple, 
but getting macro writers to agree on something is way harder


                                           Hans Hagen | PRAGMA ADE
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