Faré <[EMAIL PROTECTED]> writes: > The IRC discussion spawned by my previous bug report raised the point > of read-write invariance of #p syntax, and the fact that once again, > cmucl, sbcl and openmcl (and gcl, too) might be wrong by not > distinguishing the following: > > (MAKE-PATHNAME :DIRECTORY NIL) > => #P"" > > (MAKE-PATHNAME :DIRECTORY '(:RELATIVE)) > => #P"" > > clisp, allegro and lispworks agree that it is a good idea to print the > latter as follows > => #P"./" > [...] > The whole issue boggles my mind. Now it can boggle yours, too. > > Hopefully no more language lawyering for today.
Pathnames aren't really my bag, but I thought about this a little, and I don't think there's a problem. According to the CLHS, the directory argument to MAKE-PATHNAME must be "a valid pathname directory", where that is defined by the glossary: valid pathname directory n. a string, a list of strings, nil, :wild, :unspecific, or some other object defined by the implementation to be a valid directory component. The list (:relative) apparently doesn't qualify, unless it's "defined by the implementation...". Unfortunately, 19.2.2.5 is slightly contradictory, but says pretty much the same thing: * The directory can be a list of strings and symbols. There are * implementation-dependent limits on the list's length and * contents. and * Any component can be taken from the corresponding component of * another pathname. But that would seem to allow passing (:relative), provided you got it from some other pathname. However, 19.2.2.4.3 says this (among other things) about the directory component of pathnames: A list whose car is the symbol :relative represents a directory path starting from a default directory. The list (:relative) has the same meaning as nil and hence is not used. The list (:relative "foo" "bar") represents the directory named "bar" in the directory named "foo" in the default directory. Note the second sentence in particular. So an implementation should never give you a pathname with (:relative) as the directory component, and it seems perfectly legal for implementations to say that (make-pathname :directory '(:relative)) is either illegal, or means the same as (make-pathname :directory nil). Does that make sense? -- Todd Sabin <[EMAIL PROTECTED]>
