Re: Emacs design and architecture

[Richard Stallman]

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  > We do: just as others have noted, redisplay calls back into Lisp. Which 
  > allows us to implement jit-lock with language-specific logic written in 
  > Lisp.

To say that this happens in "redisplay" is too general to indicate
whether there is anything tricky or dangerous about it.
Calls from outer parts of redisplay are not problematical.
They are no more dangerous than calling before or after redisplay.

What would be problematical is calling from within the parts
of redisplay that alter the display matrices.  An error there
would be hard to recover.  It could crash.

It is many years since I looked at that code, but ISTR that the
calls for font lock are in the outer parts, specifically to
avoid this danger.


-- 
Dr Richard Stallman (https://stallman.org)
Chief GNUisance of the GNU Project (https://gnu.org)
Founder, Free Software Foundation (https://fsf.org)
Internet Hall-of-Famer (https://internethalloffame.org)