pari_err(): callback function instead of longjmp()

[Jeroen Demeyer <jdemeyer@cage.ugent.be>]

Hello pari-dev,

We at Sage are currently revisiting the way we do PARI error handling. I 
remind you we are using PARI-2.5.4 (but I don't think that makes such an 
important difference for this discussion).

It would be much more useful for Sage to have a callback function called 
from pari_err() instead of a longjmp(). I am talking about the following 
code:

pari_err(int numerr, ...)
{
  ...
  if (s_ERR_CATCH.n)
  {
      ...
      longjmp(*(trapped->penv), numerr);
      ...
  }

What's your opinion on adding the possibility of a callback function 
instead? If you don't like it, we're probably going to do it anyway in 
the Sage "fork" of PARI :-)

Cheers,
Jeroen.