bug#36566: 27.0.50; debug is sometimes horribly slow

[Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Lars Ingebrigtsen [2022-05-15 18:25:11] wrote:
> Stefan Monnier <monnier@iro.umontreal.ca> writes:
>>> But this reminds me -- why do we have `cl-print' anyway?
>> Because we want to let packages use `cl-defmethod` to provide their own
>> output syntax for their objects.
>>> Shouldn't the C version handle printing things nicely?
>> The C code doesn't really know about cl-defstructs (or advice objects).
> Wouldn't it make sense to teach the C `prin1' about those (and also call
> out to the Lisp level for the objects that have a specialised print
> syntax)?

Maybe it would.  I tend to think we should focus the C code on printing
data quickly and in a `read`able way (i.e. in sync with `lread.c`) and
benefit from the comfort of ELisp for the implementation of the
human-readable version of the printout where performance is not as
important because we will truncate long outputs anyway.

> We've got something vaguely similar with `print-unreadable-function',
> for instance.

This var is bound to the notion of `read`able, not "human readable",
which is why it belong in the C code (because sadly not everything can
be printed in a `read`able way).


        Stefan