On Sun, Jun 8, 2014 at 12:09 PM, Robert P. Goldman <rpgold...@sift.info> wrote: > Faré wrote: >> On Sat, Jun 7, 2014 at 8:03 PM, Robert P. Goldman <rpgold...@sift.info> >> wrote: >>> I'm still groping after a clear statement of exactly what class of bugs >>> it is that we are proposing to fix. The existing design document is >>> still too vague, proposing to fix >>> >>> "uncontrolled, unintentional leaking of readtable side effects to >>> systems that depend on such effects not happening," >>> >>> I think we need a clear example of a bug (ideally from a real system, >>> although it's fine if that bug has since been fixed) that would be fixed >>> by the change. >>> >> I probably should create test cases. >> >> Scenario A: dealing with *readtable* being bound to a new value >> 1- setup the test environment >> 2- save current packages >> 3- load fare-quasiquote (or anything that has its own readtable) >> 4- while in-readtable fare-quasiquote, load-system :force t >> something that uses normal quote, >> and see it corrupt its fasl with fare-quasiquote annotations. >> 5- delete all new packages since 2 >> 6- repeat 3, 4 — and see whether it breaks [used to] > > OK, so the bug is not that systems leak the readtable *out*, it's that > readtables leak *into* systems. I had not understood that. > > So unlike *PACKAGE*, the current (REPL) value of *READTABLE* leaks into > every system that you load. It seems to me that this is a deficiency in > CL: if CL had an IN-READTABLE equivalent to IN-PACKAGE, we would not be > having this discussion. > Oh, the outer *package* also leaks in, but people have the discipline to use defpackage and in-package, and to not shadow them away in incompatible ways.
The syntax-control branch ought to *also* set *package* to *shared-package* which should be cl-user for maximum backward compatibility, and asdf-user or something like that for maximum portability. Or maybe, like Stelian once suggested, some package that *only* has defpackage and in-package defined (maybe also uiop:define-package?), for maximum strictness. >> Scenario B: dealing with the *readtable* object being modified >> 1- setup the test environment >> 2- load and compile x1, that define #^ >> 3- load and compile x2, that uses #^ as per x1 >> 4- load and compile x3, that defines a different #^ >> 3- load and compile x4, that uses #^ as per x3 >> 4- force recompilation of x2 — it will use the definition from x4 — oops >> 5- force recompilation of x1 and x4 — it will use the definition from >> x2 — oops again > > This is the one I had in mind, and this is the one I don't think is > ASDF's problem. If x1 exported *X1-READTABLE* and ADD-X1-SYNTAX (this > function adds X1 reader macros to an existing readtable passed as > argument), then the Right Thing would simply be for X1 not to alter the > global readtable, and for X2 and X4 to explicitly employ the readtables > they want. > > This problem does not seem worthy of fixing in ASDF. > Indeed, and I'm not proposing that ASDF should do anything about it. I'm just explaining what the restriction *already is* for sane programs to never define or use conflicting readtable modifications. This restriction had to be documented (which I did with ASDF 3.1). > Scenario A seems like a stronger argument, but I'm inclined to say > "instead of limping along with a complex fix in ASDF, let's just push > NAMED-READTABLES use and leave ASDF alone." > > NAMED-READTABLES seems like a much better fix than complicating ASDF > further, because it gets at the root of the problem, instead of > band-aiding around it. > > The counter-argument, I suppose, is that Scenario A can only be fixed if > *EVERYONE* fixes their code to put IN-READTABLE at the top of their > source files, just the way we have to put IN-PACKAGE at the head of > every source file. > Exactly. Unless you're demanding that every library should depend on named-readtables and use it, that doesn't work. And even then, you'd forbid any readtable that is incompatible enough with the standard one to interfere with the evaluation of the in-readtable form, e.g. a readtable for Python syntax, etc. — or even something as innocuous as fare-quasiquote, if a file uses ` before in-readtable. This can't fly. And named-readtables itself can't depend on named-readtables. In the end, you'd have to move it into ASDF, which is more complex than the simple use of *shared-readtable*. > My question here came from thinking only about your Scenario B, and > overlooking Scenario A. > > I'm starting to reluctantly come around, but I still need to figure out > how my system went up the spout when using syntax-control ASDF. If I > can't answer on my own behalf, I can hardly claim to understand the > patch well enough to apply it.... > If I can help with this understanding, I'm at your service to inspect code of discuss behavior. —♯ƒ • François-René ÐVB Rideau •Reflection&Cybernethics• http://fare.tunes.org Guns & bullets don't kill people — blood loss and organ damage kills people. _______________________________________________ Asdf-devel mailing list Asdf-devel@common-lisp.net http://common-lisp.net/cgi-bin/mailman/listinfo/asdf-devel
