On Fri, Mar 14, 2014 at 6:10 PM, Robert Goldman <rpgold...@sift.net> wrote: > Quick follow-up: what about blowing this discussion into launchpad under > the rubric of "Manage CL syntax" or something like that. > > I would prefer not to lose the discussion. > > I believe this is a place where a tool like POIU or XCVB really veers > away from vanilla CL usage. > > Vanilla CL usage encourages* actions during building that side-effect > the global state of the image. These actions may be bad if one wishes > to build individual components in multiple different CL images. But > they are natural to people developing code incrementally and > interactively using a REPL. > > I don't want ASDF to drift into being a tool that prescriptively moves > people away from that practice. I think that's too presumptive for a > piece of infrastructure. I don't think it's my job to wreck code, just > because it's bad style. And I don't think proper use of the readtable > or of pretty-print dispatch is obvious enough that people will recover > well if we mess with it. > > As you have said, I am inclined to be much more conservative about > changes like this. > Here is my theory: safe code needs to respect hygiene, because you never know which system are loaded before or after: it depends on the overall plan of the toplevel target system. Therefore is it never correct to rely on other systems having set a particular readtable, and it is never correct to side-effect the current readtable into something that modifies standard characters — or any character that any other program might want to use, for the matter. If you side-effect the readtable, and the readtable escapes, you are going to hurt someone, somewhere.
In the current setup, it is therefore a bug if you side-effect the readtable, and those programs that do are buggy. Using named-readtables is fine, but only if you reset the readtable to the standard one at the end of every file, or have a method that binds *readtable* around your compilation. I see two ways forward: (1) recognize that it is a bug, and help programmers by being strict, modulo some compatibility mode for older systems until they are fixed, or (2) slightly change the semantics so that it's not a bug anymore, by making the readtable either per-file or per-system; then you can modify the readtable to your heart's content, because it's private. My initial reaction was (1), and that's more or less the patch I sent to anton, who tells us it breaks a lot of things. At Anton's suggestion, I considered (2) and it looks promising — but we need to modify the protocol and/or use a new method-combination to achieve the effect in a backward compatible way. —♯ƒ • François-René ÐVB Rideau •Reflection&Cybernethics• http://fare.tunes.org The only way to have a friend is to be one. — Ralph Waldo Emerson
