On Wed, 06 Apr 2011 05:59:48 -0500 Ted Zlatanov <tzz@lifelogs.com> wrote: 

TZ> Since hashtables can get pretty big, it would be nice to have a
TZ> separator between entries when they are printed.  Could that be provided
TZ> at the top level, e.g.

TZ> (let ((hash-table-print-separator "\\\n"))
TZ>    (format "%S" my-hash-table))

TZ> or in some other way?  It would make large hashtable dumps like the ones
TZ> from the new registry.el and gnus-registry.el much easier to read and
TZ> debug.  In the old gnus-registry.el I had special code to break up
TZ> alists like that but it was slow so I'd rather ask Emacs to do it for
TZ> me at the C level.

The attached patch introduces `list-print-separator' to be used for list
and hashtable entries.  It's printed unescaped.  It could be a function
too, to be called with the print level.  For me it's sufficient as a
simple object to be printed.

Let me know what you think...

Thanks
Ted