On 1/24/10 Jan 24 -2:02 PM, Tamas Papp wrote:

Hi,

I am the author of the cl-cairo2 library. Cairo itself is a graphics library, and my library provides a Lisp interface.

Some of the features (eg drawing in X11, Windows or Quartz) are platform dependent. Currently, the approach of cl-cairo2 is to provide extra system definitions for these, eg an X11 user would load the systems cl-cairo2 and cl-cairo2-x11 manually. I am wondering if there is a better way to do platform-dependent loading.

The solution I was thinking of was to try loading the platform dependent shared C libraries using CFFI, and set some flag (or push something to *features*) if they succeed, but if they fail, capture the condition with handler-case and just proceed with a warning. Then I could load platform-dependent code conditionally on this --- but I don't know how to do that in ASDF.

Please tell me what is the "right way" to do these things (ie stuff that I put in features). Examples of libraries that load platform-dependent code conditionally with ASDF would also help.

You might try looking at CL-SQL, which has multiple backends. Or McCLIM.

I believe that the :if-component-dep-fails argument was intended to be used for this --- you specify a dependency on a feature together with a failure strategy that moves on to the next alternative --- but this is not adequately documented, and I've never found it to be a particularly clear way of specifying a behavior. I'm not sure why having a feature dependency combined with a dependency failure handler is a more happy substitute for just using #+

Christophe Rhodes has, I believe, on occasion pointed to an example that uses this mechanism, but I don't have a good pointer to it.

If you can find a good solution to this problem, please post it to the list, and I will try to see that it gets into the manual.

cheers, r