[Dev-luatex] return value of filter callbacks

Khaled Hosny khaledhosny at eglug.org
Fri Nov 5 14:22:06 CET 2010

On Fri, Nov 05, 2010 at 01:59:54PM +0100, Manuel Pégourié-Gonnard wrote:
> Hi,
> Sorry if this is very clear from the manual, maybe I just didn't read the part
> where it is explained (or I read it but was too stupid/tired to notice), but I
> don't understand the meaning of the return value of some callbacks.
> The first example (by order of apparition in the manual) is
> pre_linebreak_filter, whose calling convention is:
> function(<node> head, <string> groupcode)
>     return true | false | <node> newhead
> end
> I think it's clear what returning a newhead node does, but I don't understand
> what returning true or false means for this callback. Other similar callbacks
> include post_linebreak_filter, (h|v)pack_filter, pre_output_filter, etc.

I think it is explained in section 4.1:

  For some minor speed gain, you can assign the boolean false to the
  non-file related callbacks, doing so will prevent LuaTeX from executing
  whatever it would execute by default (when no callback function is
  registered at all). Be warned: this may cause all sorts of grief unless
  you know exactly what you are doing! This functionality is present since
  version 0.38.

Not sure about "true" though.


 Khaled Hosny
 Arabic localiser and member of Arabeyes.org team
 Free font developer

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