Re: Merging scratch/no-purespace to remove unexec and purespace

[Pip Cet]

Gerd Möllmann <gerd.moellmann@gmail.com> writes:

> Pip Cet via "Emacs development discussions." <emacs-devel@gnu.org>
> writes:
>
>> "Stefan Monnier" <monnier@iro.umontreal.ca> writes:
>>
>>>>> OTOH and IMHO, it would be preferable if that symbol could not crash
>>>>> Emacs.  Can we come up with a good way to fix that, while preserving the
>>>>> check that Andrea wants to keep?
>>>>
>>>> That sounds like a good thing to focus on, yes.  We need to have a value
>>>> in a vector that we Fread that is distinguishable from all other values.
>>>
>>> How 'bout an uninterned symbol `#:foo`?
>>
>> I think those are legal for native-compiled subrs to use (there's a
>> comment about it, at least), so that wouldn't do us any good, would it?
>>
>> Pip
>
> Uninterned symbols are unique, i.e. (eq '#:a '#:a) => nil.
> Wouldn't that help?

I don't see how, sorry.  Nativecomp produces a string in the .eln file
that is passed to make_string(), then to Fread().  The string can
include source code for uninterned symbols, but there's no way for us to
tell whether a #:lambda-fixup in there was put in by us or by the user.

What we could do is expand read so this:

(let* ((cookie (cons nil nil))
       (read-table (list (cons "cookie" cookie)))
       (result (read "#s(cookie cookie)")))
   (eq result cookie))

to return t.  Then we'd have an expressive syntax for this kind of
thing (obviously, "cookie" should be something useful in the #s(...)
syntax.

A slightly different option is to do this:

(let* ((cookie (cons nil nil))
       (read-circle (list (cons 1 cookie)))
       (result (read "#1#")))
   (eq result cookie))

in effect allowing us to use prime the read-circle table with
externally-provided objects.

Pip