[asdf-devel] standard io syntax woes

[Pascal Costanza]

You could specify an extension to Common Lisp that allows users to request read-only readtables, submit this as a CDR, and hope that CL implementations are willing to implement such an extension of the language, and then rely on that.

Pascal

On 20 Feb 2013, at 22:44, Faré <fahree at gmail.com> wrote:

> 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)
> 
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--
Pascal Costanza