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: rpgoldman@SIFT.net