[asdf-devel] [cclan-list] How to depend on a system optionally?

[Robert Goldman]

Gary King wrote:
> I share Robert's queasiness and also think that we want ASDF to support
> these sorts of dependencies (simple, weak, contingent, etc... (?)).
> 
> I'm going to update the manual with James's table (thanks James!) in the
> hopes of giving us a place to hang our collective hats.
> 
> 

That sounds like a good idea, modulo it would be great to put it in some
new section like "TODO list" or "Missing bits in implementation."

How about pushing my documentation of weakly-depends-on at the same
time?  Possibly with some warning that the implementation of this may
change.

Suggestion:  instead of using a trick to get the square peg
:weakly-depends on logic to sorta fit in the round-hole :depends-on
slot, which forces us to (inappropriately, IMO) evaluate this stuff at
macroexpansion time, I think we should suck it up and add extra slots
for weak dependencies and contingent dependencies.

Follow-on suggestion:  we need to think about what happens when a
component has all possible combinations of :depends-on,
:weakly-depends-on, and :contingent-on.  Does something that would not
be loaded because of :contingent-on avoid a crash that would come from a
violated :depends-on?

Extra bonus follow-on:  are these expected to be meaningful when the
depended-on item is a system (clearly yes), a feature (seems handy), an
arbitrary component (what would this mean?)?

Best,
r