Hi Don,
System configuration, and configuration of dependencies in particular, is
in some sense an AI-complete problem. There is no general-purpose
solution. Every solution has tradeoffs. At the end of the day, some end
user may need to tweak something.
My impression is that that Quicklisp takes the 80% or 90% approach.
Quicklisp tries to provide what "the average" user wants. Anyone outside
that profile should download and configure packages independently.
From what you describe, sqlite adds minimal functionality to Roan, and
requiring sqlite adds significant risk of a failed Roan install. Thus
sqlite should not be required in the Quicklisp distribution of Roan.
Power users can read the documentation, download Roan, and do any manual
tweaks that are required.
In terms of functionality and soundness of intent, the most advanced
configuration tool I know of is GNU Autoconf. It provides a standard
approach for running experiments on a system, providing default config
selections, and providing user-selectable options. Unfortunately, it
targets C/C++ and is written in "portable shell script" that is
partially auto-generated by M4 and Perl. In other words, it is fairly
hard to grok. Unfortunately, CL has nothing that even comes close in
terms of functionality.
I haven't looked recently, but in the past there were a number of ASDF
files with reader conditionals (or comments) in order to support some user
customization. I believe Fare got many of these cleaned up. You should
ask the ASDF list for the current recommended practice.
- Daniel
On Wed, 6 Apr 2016, Don Morrison wrote:
I'm tidying up a library of code, Roan (for building things that play with
change ringing, you probably don't want to know the details :-), for eventual
inclusion in Quicklisp. In thinking about its dependencies I've run into an
issue I'm not sure how best to address. I asked Zach Beane for advice, but he,
too, isn't sure how best to deal with it, and suggested I consult folks on this
list.
My library has dependencies upon several others, all readily available from
Quicklisp. One them, though, cl-sqlite (or perhaps it's better referred to as
sqlite, it's rather conflicted about what it wants to call itself) in turn has
a dependency on a binary library, sqlite3. For example, if the sqlite3 binary
library is not install, doing
(ql:quickload :sqlite)
signals an error when it's setting up FFI things.
However Roan's use of SQLite is not essential to Roan's usefulness (well, it's
probably not all that useful to most people anyway, only to those interested in
change ringing, a small audience). There's really only one, tiny corner of
functionality in Roan it supports. While sqlite3 is easily obtained, it would seem polite
to allow use of Roan without it, simply disabling the two functions that depend upon it.
The "disable if the cl-sqlite stuff is not present"
part I can easily do. What's causing me to scratch my head is figuring out how
to set things up so Roan will still install whether or not the sqlite3 binary
library is present.
Three unattractive possibilities that come to mind are
- Define two different roan ASDF systems: one consisting of most stuff, without the
SQLite-dependent bits, and the other the "real" one that loads the first plus
cl-sqlite. Then the user picks which one to load based on need.
- Define something to push onto *features* that, if present, comments out in
roan.asd the dependency on cl-sqlite, etc. Then the user has to push the
appropriate keyword onto *features* before loading roan, if she doesn't have
sqlite3.
- I'm guessing I could probably include some code in the roan.asd file that
does something or other nasty looking for the binary library, and then adjusts
the defsystem appropriately or something (ugh).
None of these is particularly appealing. The first two seem to put too much on
the shoulders of the poor luser who just wants to load the darn thing without
having to think about lower level stuff, and the last (a) seems to confound
too much actually doing complex, kludgy stuff with what should be just
declarative, and (b) is something I seriously doubt I'd get right, especially
in a portable way.
It seems there has got to be A Better Way. Has anyone dealt with a similar
situation? Or, even if not, might you have a good idea?
I suppose an attractive possibility might be to wrap some sort of condition
handler around the place inside ASDF that's trying to load the cl-sqlite
dependency, but I don't know my way around the ASDF internals enough to have a
sense
of where that should be done, or if it's even practical. Is there a good place
inside of ASDF to do such a thing? It seems fairly modular, so it seems likely.
Maybe it's as easy as defining a specialized method of some sort, or an
:around method on something or other?
Thanks!
--
Don Morrison <[email protected]>
"There were two cultures, as far as he was concerned. One was the real
one, the other was occupied by people who liked machinery and ate
pizza at unreasonable hours." -- Terry Pratchett, _The Last Hero_
