Re: 23.0.50; savehist save invalid syntax

[Davis Herring]

>     With this much complexity, my temptation would be to provide a
>     print-readable function (or an optional argument to an existing
> printer)
>     that signalled if it  were asked to print something that has no read
>     syntax.
>
> I wouldn't mind adding that feature if someone wants to do it.
> It should be controlled by a variable.

I've implemented that feature.  I took Stefan's suggestion and made the
variable be a function that took over printing (or t for signaling as in
my original suggestion).  The patch is attached; please bear with me as I
think it's my most complex foray into Emacs' C thus far and introduces a
new macro and such.  It is, however, tested.

On a side note, I see that this is an extension of the variable
`print-readably' in XEmacs.  It doesn't follow naming convention, but
perhaps my new variable `print-unreadable-function' should be named or
aliased to `print-readably' for compatibility.

Meanwhile, savehist needs to use this.  It actually already has a hack in
it that uses `prin1' and `read' (or `print-readably' on XEmacs) to detect
unreadability; one could certainly use this instead of the new printing
feature.  But for cleanliness and completeness, I removed that trick and
replaced it with handlers for the unreadable signals that, now, both
varities of Emacs will generate.  (Of course, I also actually implemented
the code to skip unprintable history elements, instead of skipping the
entire history or so.)  This second patch is completely untested because
I'm unfamiliar with savehist.

Davis

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print-unreadable.patch
Description: Binary data

savehist-unreadable.patch
Description: Binary data