Liam Healy wrote: > Well, I think it has some use, though now in the Quicklisp era it's less > important, and that is to define an optional dependency for something > that's incidental to the main system. For example, one of my projects > (Antik) defines units as part of a large system for doing > science/engineering math. As a convenience, it will use the degree > symbol. In order to get the degree symbol, I use cl-unicode. This is an > incidental use of one (big) system for the occasional (cosmetic) > augmentation of another. Most people will not care about units at all, > and so loading cl-unicode grows the system mostly unnecessarily, and > adding a new user-visible system definition complicates users' mindspace > for a mostly unused benefit (and imagine you have 3 optional definitions > like this - then you would need to define 7 new systems to capture each > combination). The alternative is to give up on the degree symbol, but it > is nice to have it when you use degrees, and easy (one line of source > code) to add if cl-unicode is present.
Wouldn't it be sufficient to: 1. Weakly depend upon the cl-unicode system. This will load the cl-unicode system if available, but ignore it (instead of failing the load) if cl-unicode is not present. 2. Detect the successful load or failure downstream in a file-component that adds the degree symbol. Something like (:component "turn-on-unicode-symbols" :if-feature :cl-unicode) I note that this conflicts with Faré's advice in the current manual, which is to use asdf-system-connections *in place of* weakly-depends-on. I am removing that advice, given that A-S-C is deprecated. Question for Faré: you say that weakly-depends-on is not deterministic, and that it's effects depend on load order. Off-hand, I don't see this. If I have a system A that weakly-depends-on B, and then a component, as above, that uses if-feature, where does the order-dependence arise? Indeed, w-d-o seems more deterministic than A-S-C, because the latter tries to load if B is already loaded -- and NOT try to load B if it's not there. That means that A-S-C is more procedural (depending on global state) and less declarative than W-D-O, not less. Or I'm missing something about the semantics. cheers, r -- Robert P. Goldman Staff Scientist Smart Information Flow Technologies (d/b/a SIFT, LLC) 319 1st Ave N., Suite 400 Minneapolis, MN 55401 Voice: (612) 326-3934 Email: rpgold...@sift.net
