I'm OK with declaring DEFSYSTEM-DEPENDS-ON a failure, and load-system (or load-systems) the official way to go. But
1- This of course requires heads up, updating all users before retiring the feature, etc. From my experience, if you start seriously deprecating today and sending patches to all authors who use it in quicklisp, you can expect to be removing that part of the code in two years or so.
2- To make these dependencies work properly still requires modifying ASDF to add explicit plan nodes for loading ASD files, that will contain the systems loaded by load-system. The same trick will also automatically make the :defsystem-depends-on work, since it itself calls load-system.
3- Yes, defining things in the ASDF package is ugly, but extensions are few enough, and using a prefix is a good enough namespace management strategy. Not the most horrible thing that working with CL does to you.
4- Yes, at some point, a better Lisp than CL will be needed. And Haskell isn't quite it. Neither is Scheme or Clojure, I fear. Maybe some future version or variant of Racket.
—♯ƒ • François-René ÐVB Rideau •Reflection&Cybernethics• http://fare.tunes.org Who released the most slaves? The one who spent his wealth buying them back? Or the capitalist who found a way to power mills with water? — Paul Claudel
On Fri, Feb 12, 2016 at 3:11 PM, Robert Goldman rpgoldman@sift.net wrote:
On 2/11/16 Feb 11 -8:12 PM, Faré wrote:
On Wed, Nov 18, 2015 at 8:59 AM, Robert Goldman rpgoldman@sift.net wrote:
Commonly, one wants to extend ASDF with new operation and component classes.
But the support in ASDF for referencing such classes all involves automagically interpreting keyword symbols (and some unqualified symbols?) in the ASDF package.
If I understand this correctly, this leaves the ASDF extender with the alternatives of either jamming their new symbols into the ASDF package late, and exporting them, or having them live in a new package, which is cleaner, but relegates these new components to second-class status.
Consider the following
[...snip....]
The problem is that the defsystem form is read before the :defsystem-depends-on clause can be processed, and hence any symbol used in the defsystem form MUST be in a package that is already defined by the time the defsystem form is read. If you stick to a purely declarative style of not having definitions in your .asd file, that pretty much means only the asdf and keyword packages are allowed.
defsystem-depends-on is also broken in that ASDF assumes that it doesn't mark such extensions as needing to be reloaded and the .asd files that use them reprocessed should these extensions or their dependencies be modified.
On the one hand, ASDF is very wrong. On the other hand, side effects everywhere mean that even if we ever fix that wrong (which will be a lot of work), there's still a lot of wrong in trusting extensions to not have persistent side-effects.
This is very frustrating to me.
In the old days, we would just put
(asdf:load-system "extension")
at the top of the file. Everybody said "oh, noes! side effects!"
So we added DEFSYSTEM-DEPENDS-ON.
This adds a truckload of complex code to ASDF that we must maintain, but basically doesn't fix anything:
- The extensions don't work like native-to-ASDF constructs, unless you
put them in the ASDF package, so we are encouraging programmers to perpetrate name collisions.
Note that the "bad" side-effecting construct is *BETTER* than this, because the load form can be put upstream of a defpackage in the asd file, so that the symbols will exist before the DEFSYSTEM is read. This means that ASDF extenders are *not* encouraged to mess up the ASDF package.
- The dependencies, as you point out, are broken. Indeed, they may be
*more* broken than when we put ASDF:LOAD-SYSTEM forms in the file.
The only thing that DEFSYSTEM-DEPENDS-ON fixes, then, is introspection. But a *declaration*, instead of a semantic form would solve this problem, in a much simpler way.
I suggest that DEFSYSTEM-DEPENDS-ON should turn into a declaration. I.e., it should provide introspection semantics for, e.g., quicklisp, but that's it. To keep stupid things from happening, it should error out if the depended-on system is not loaded at the time the follow-on system is loaded. That's it. End of story.
Simplification ensues, as opposed to us having to maintain fussy propagation code.
Also, we stop encouraging people to bork the ASDF package, which is A Bad Thing to do.
Indeed, it's tempting to package lock ASDF on lisps that support that operation....