Subject: Re: #+,#- etc. (Re: Behaviour of #'directory) From: Erik Naggum <email@example.com> Date: Thu, 07 Mar 2002 01:46:56 GMT Newsgroups: comp.lang.lisp Message-ID: <firstname.lastname@example.org> * Kent M Pitman | Did it allow for multiple cases? The usual problem that alternatives to | #+/#- try to address is the desire for #+otherwise. That is, when you | have | | #+(or Genera (and (not Win32) Franz)) (foo) | #+(and CLIM (not PDP10)) (bar) | #+(or (not CLIM) linux) (baz) | | you sometimes wonder what cases are not handled. of course you could | write: | | #-(or Genera (and (not Win32) Franz) (and CLIM (not PDP10)) (not CLIM) linux) | | but you might forget to edit it if another case is inserted. Suppose this is used to support a particular feature, say mumble-frotz. Each positive form could then provide the feature. A minute amount of macrology should make it possible to provide a feature more easily. Maybe something like this: (defmacro maybe-provide-feature (feature &body body) (when body `(progn ,@body (pushnew ,feature *features*)))) Then we could simply wrap the above example in like this: (maybe-provide-feature :momble-frotz #+(or Genera (and (not Win32) Franz)) (foo) #+(and CLIM (not PDP10)) (bar) #+(or (not CLIM) linux) (baz)) #-mumble-frotz (error "mumble-frotz is unavailable on this system") ; or whatever /// -- In a fight against something, the fight has value, victory has none. In a fight for something, the fight is a loss, victory merely relief.