[asdf-devel] standard io syntax woes

[Faré]

In 2.29.9, I pushed a change whereby ASDF keeps passing around whichever value
the two syntax tables are globally bound to, leaving on the user the
onus to not mutate
them in too destructive a way, yet without precluding a change.

Allocation is for (copy-readtable nil) and (copy-pprint-dispatch nil) is
1648 and 2192 bytes respectively on CCL 1.9 x86-64, and
more like 5300 and 10300 bytes on SBCL 1.1.3 x86-64.
rme suggests that 15KiB per .asd file is no big deal and we should
just bite the bullet.

Others suggest that we should let users fail and keep out of the business
of binding syntax variables altogether. I'd agree if I didn't want to
eventually move
towards "pure" .asd files in a restricted standardized syntax as per
https://bugs.launchpad.net/asdf/+bug/541562

If only Common Lisp allowed to portably specify read-only tables,
I would just use that, and let users fail when they try to mutate them.
Unhappily, it doesn't, and therefore when some user mutates a global table,
it will end up causing pain for another user, not himself.
Or I could rely on SBCL being used a whole lot and indeed having
immutable such default syntax tables with understandable messages
to blame whoever tries to mutate those tables without rebinding them first,
and push for all implementations to similarly make them read-only.

The jury is still out. Please voice your opinion.

—♯ƒ • François-René ÐVB Rideau •Reflection&Cybernethics• http://fare.tunes.org
Statism is the secular version of salvation through faith: it doesn't
matter what bureaucrats do, only that they do it with good intentions.


On Wed, Feb 20, 2013 at 3:44 PM, Faré <fahree at gmail.com> wrote:
> Dear Common Lisp hackers,
>
> Inspecting with Anton Vodonosov the latest batch of cl-test-grid issues
> when running with asdf 2.29.x, we found an interesting case
> that mirrors the previous failure of iolib 0.7.3 with 2.29.
>
> In the hope of making the semantics of asd files more deterministic,
> with an eye on eventually making .asd files a strict subset of Lisp,
> I had put in 2.27 a with-standard-io-syntax around the loading of a .asd file.
> However, this is specified to bind *readtable* and *print-pprint-dispatch*
> to standard tables that are notionally read-only,
> though this immutability is NOT enforced on most implementations,
> instead there being unspecified bad consequences if you do mutate.
>
> So, I could conceivably (copy-readtable nil) and (copy-pprint-dispatch nil)
> every time, but that could be expensive on some implementations.
> Or I could say "it's the programmer's responsibility to ensure a proper
> table has been setup before he modifies it",
> but that would be harsh and a notable backward incompatibility
> (and there's no equivalent of named-readtables for pprint-dispatch).
> Or I could preserve the current semantics of a global table
> that everyone modifies causing "interesting" issues, by rebinding
> *print-pprint-dispatch* as well as *readtable* within the w-s-i-s,
> only ensuring that the other syntax variables are standard.
> Or I could remove the with-standard-io-syntax altogether, and say
> "yes, if you're doing any global modification, you suck and you're
> going to break something for someone, but that's none of my business".
>
> Anton leans for the latter.
>
> —♯ƒ • François-René ÐVB Rideau •Reflection&Cybernethics• http://fare.tunes.org
> One can be so anxious to put his "best foot forward" that he doesn't even
> notice that it isn't his own foot. — Harry Browne (HIFFIAUW)