Agreed. If we claim that a directory is a pathname 'without" a
filename, then the three ways (so far) for a filename to be missing
are for it to be `nil`, the empty string or :unspecific, Here's
another crack at it and a sort-of test
> (defun directory-pathname-p (pathname)
> "A directory-pathname is a pathname _without_ a filename. The three
> ways that the filename components can be missing are for it to be
> `nil`,
> `:unspecific` or the empty string."
> ;; a rather ugly implementation of the docstring
> (let ((null-components (list nil :unspecific "")))
> (flet ((check-one (x)
> (not (null (member (pathname-name pathname) null-components
> :test 'equal)))))
> (and (check-one (pathname-name pathname))
> (check-one (pathname-type pathname))))))
#+(or)
;;test
(every (lambda (p)
(directory-pathname-p p))
(list
(make-pathname :name "." :type nil :directory '(:absolute "tmp"))
(make-pathname :name "." :type "" :directory '(:absolute "tmp"))
(make-pathname :name nil :type "" :directory '(:absolute "tmp"))
(make-pathname :name "" :directory '(:absolute "tmp"))
(make-pathname :type :unspecific :directory '(:absolute "tmp"))
(make-pathname :name :unspecific :directory '(:absolute "tmp"))
(make-pathname :name :unspecific :directory '(:absolute "tmp"))
))
On Jul 13, 2009, at 1:57 PM, Richard M Kreuter wrote:
> Gary King writes:
>
>>> OK, I /have/ misdiagnosed this. The logic seems actually busted in
>>> directory-pathname-p. The problem is that, at least on allegro, you
>>> can get a valid directory pathname whose name component is neither
>>> NIL, nor :unspecific, but "" (the empty string).
>>
>> Ugh,
>>
>>> (member (pathname-name pathname) (list nil "" :unspecific) :test
>>> 'equal)
>>
>>
>> A source of the problem are pathnames that arise from things like
>> this:
>>
>>> (make-pathname :name "" :directory '(:absolute "tmp"))
>> #p"/tmp/"
>>> (pathname-name *)
>> ""
>>
>> Added a call to namestring seems to be another way to canonical
>> things
>> so I think this will also work and feels (to me) a bit more portable:
>>
>> (defun directory-pathname-p (pathname)
>> (let ((pathname (namestring pathname)))
>> (and (member (pathname-name pathname) (list nil :unspecific))
>> (member (pathname-type pathname) (list nil :unspecific)))))
>
> I see two problems:
>
> (1) If the the host component of *DEFAULT-PATHNAME-DEFAULTS* is
> different than the host component of PATHNAME, the parse might fail
> or come out wrong.
>
> (2) Pathnames with "" for the name component don't have namestrings
> under SBCL. (IIUC, the intent there is to try to have namestring
> parsing and unparsing be non-lossy.)
>
> I think it might do just as well to say that "" for the name counts
> the
> same as NIL or :UNSPECIFIC for DIRECTORY-PATHNAME-P, unless somebody
> knows of implementations that don't work that way.
>
> --
> RmK
--
Gary Warren King, metabang.com
Cell: (413) 559 8738
Fax: (206) 338-4052
gwkkwg on Skype * garethsan on AIM * gwking on twitter
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