bug#52566: 29.0.50; Wishlist: There should be a print-unreadable-function variable

[Lars Ingebrigtsen]

It should be called from print_vectorlike (and any other places that
print unreadable objects, but I'm not sure there are any other places),
and should probably have a signature like

OBJECT PRINTCHARFUN ESCAPEFLAG

If it returns nil, the object should be printed as normal.

This can then be used to implement a `readablep' function (that would
bind this to a function that signals an error, and then catch that
error), and also to possibly make an alternative version of prin1 that
returns whether it printed something unprintable.


In GNU Emacs 29.0.50 (build 69, x86_64-pc-linux-gnu, GTK+ Version 3.24.30, 
cairo version 1.16.0)
 of 2021-12-16 built on xo
Repository revision: e7a6d6a546e7e56e5a721aac86a19473e4303111
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12013000
System Description: Debian GNU/Linux bookworm/sid


-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no