[Dev-luatex] return value of filter callbacks

Khaled Hosny khaledhosny at eglug.org
Fri Nov 5 14:27:32 CET 2010

On Fri, Nov 05, 2010 at 03:22:06PM +0200, Khaled Hosny wrote:
> 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.

Please ignore this, I just confused things up.


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

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