bug#25606: [DRAFT PATCH 2/2] Signal list cycles in ‘length’ etc.

[Eli Zaretskii]

> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Wed,  1 Feb 2017 15:56:22 -0800
> Cc: Paul Eggert <eggert@cs.ucla.edu>
> 
> Use macros like FOR_EACH_TAIL instead of maybe_quit to
> catch list cycles automatically instead of relying on the
> user becoming impatient and typing C-g.

I don't think this is a good idea.  We don't know when the user will
become impatient, and on busy systems the counter could be very low by
that time.  I think we shouldn't second-guess users this way, and
should always leave them the possibility of interrupting a possibly
prolonged calculation.

Also, could we please have tests for these functions?

Thanks.