PATHNAME-COMPONENT-VALUEThe restrictions are not all written down in one place, but they appear to be as follows:
Host nil, :wild, string, or list of strings Device nil, :wild, string, or something else ("structured") Directory nil, :wild, string, or something else ("structured") Name nil, :wild, string, or something else ("structured") Type nil, :wild, or string Version nil, :wild, :newest, positive integer, implementation dependent symbol, or implementation-dependent integer less than or equal to zero. Suggestions include :oldest, :previous, :installed, 0, and -1.
PATHNAME-UNSPECIFIC-COMPONENT:NEW-TOKEN allowed implementations to allow any component to be :UNSPECIFIC. This has been voted in.
PATHNAME-SUBDIRECTORY-LIST proposes a list of strings and keyword symbols for the directory component.
PATHNAME-CANONICAL-TYPE proposes some new operations but does not change the possible values of the type component.
PATHNAME-WILD proposes a portable way to test for implementation dependent component values that indicate wildcard matching. It does not change the possible values of any component.
0. Pathname component value strings never contain the punctuation characters that are used to separate pathname fields (e.g. slashes and dots in Unix). Punctuation characters appear only in namestrings. Characters used as punctuation can appear in pathname component values with a non-punctuation meaning if the file system allows it (e.g. a Unix file name that begins with a dot).
When examining pathname components, conforming programs must be prepared to encounter any of the following values:
1. Any component can be NIL, which means the component has not been specified.
2. Any component can be :UNSPECIFIC, which means the component has no meaning in this particular pathname.
3. The device, directory, name, and type can be strings.
4. The host can be any object, at the discretion of the implementation.
5. The directory can be a list of strings and symbols as detailed in PATHNAME-SUBDIRECTORY-LIST (this assumes that it passes.)
6. The version can be any symbol or any integer. The symbol :NEWEST refers to the largest version number that already exists in the file system when reading, overwriting, appending, superseding, or directory listing an existing file, and refers to the smallest version number greater than any existing version number when creating a new file. Other symbols and integers have implementation-defined meaning. It is suggested, but not required, that implementations use positive integers starting at 1 as version numbers, recognize the symbol :OLDEST to designate the smallest existing version number, and use keyword symbols for other special versions.
Wildcard pathnames can be used with DIRECTORY but not with OPEN, and return true from WILD-PATHNAME-P (if issue PATHNAME-WILD passes). When examining wildcard components of a wildcard pathname, conforming programs must be prepared to encounter any of the following additional values in any component or any element of a list that is the directory component:
7. :WILD, which matches anything.
8. A string containing implementation-dependent special wildcard characters.
9. Any object, representing an implementation-dependent wildcard pattern.
When constructing a pathname from components, conforming programs must follow these rules:
a. Any component can be NIL. NIL in the host may mean a default host rather than an actual NIL in some implementations.
b. The host, device, directory, name, and type can be strings. There are implementation-dependent limits on the number and type of characters in these strings.
c. The directory can be a list of strings and symbols as detailed in PATHNAME-SUBDIRECTORY-LIST (this assumes that it passes.) There are implementation-dependent limits on the list's length and contents.
d. The version can be :NEWEST.
e. Any component can be taken from the corresponding component of another pathname. When the two pathnames are for different file systems (in implementations that support multiple file systems), an appropriate translation occurs. If no meaningful translation is possible, an error is signalled. The definitions of "appropriate" and "meaningful" are implementation-dependent.
f. When constructing a wildcard pathname, the name, type, or version can be :WILD, which matches anything.
g. An implementation might support other values for some components, but a portable program cannot use those values. A conforming program can use implementation-dependent values but this can make it non-portable, for example, it might work only with Unix file systems.
Consequences:
The changes relative to CLtL plus PATHNAME-UNSPECIFIC-COMPONENT are as follows:
The removal of punctuation characters during parsing is specified.
"Structured" components are disallowed in non-wildcard pathnames, except for the specific structuring of directories specified in issue PATHNAME-SUBDIRECTORY-LIST.
"Structured" hosts are allowed, a generalization of CLtL's list of strings.
The type and version can be "structured" in wildcard pathnames.
The difference between what component values a program can depend on being able to use, versus what component values a program must be prepared to encounter, is clarified.
The implementation-dependent variations are identified explicitly.
Adding "structured" hosts conforms to current practice.
Substituting a default host for NIL conforms to current practice in implementations that require all pathnames to have a specific host.
Confining "structured" devices and names to wildcard pathnames, and replacing "structured" directories with an explicit specification of the form of the directory value, should improve portability without causing any harm.
:WILD is only required to be supported in the name, type, or version, which are the easiest to implement and the most useful in applications.
PATHNAME-SUBDIRECTORY-LIST, but otherwise conforms to PATHNAME-COMPONENT-VALUE:SPECIFY.
Like Genera, the Explorer current practice is to use an object instead of a string for the host component. The directory component is a list of strings, not yet supporting the symbols specified in proposal PATHNAME-SUBDIRECTORY-LIST; other than that, the Explorer conforms to proposal PATHNAME-COMPONENT-VALUE:SPECIFY.
Macintosh Allegro Common Lisp 1.2.2 uses NIL and "" for :UNSPECIFIC, and uses a string with punctuation characters instead of a list for the directory. MAKE-PATHNAME won't set a component to NIL when :DEFAULTS is used, it merges with the defaults instead. Otherwise it seems consistent with what is proposed.
Lucid Common Lisp 3.0.1 under Unix uses NIL for :UNSPECIFIC, and uses a list for directories of somewhat different form from what is proposed in PATHNAME-SUBDIRECTORY-LIST. Lucid lets you store arbitrary information in the version field with MAKE-PATHNAME :VERSION and will return it with PATHNAME-VERSION (as long as it's a symbol or an integer), even though it's not used. Otherwise it seems consistent with what is proposed.
Ibuki Common Lisp Release 01/01 behaves the same as Lucid, including the same form of structured directory, except it doesn't have the ability to store information in the unused pathname version field, and it has the same bug in MAKE-PATHNAME that the Macintosh has. Otherwise it seems consistent with what is proposed.
Other implementations were not surveyed.
This proposal assumes that no current or planned implementation uses "structured" names except possibly for wildcards.
PATHNAME-UNSPECIFIC-COMPONENT and PATHNAME-SUBDIRECTORY-LIST, so the cost of this proposal itself should be minimal. It is conceivable that an implementation may exist that has to change its pathname representation, for example one that uses numbers as "structured" devices. Some implementations may have to change their treatment of punctuation characters.
As I've said before, I don't think that trying to construct or pick apart pathnames by component can be accomplished portably in any case, because even if you restrict the representation of what can appear in the various components, the objects you stuff in may or may not make sense for a particular file system. Instead, I would much prefer to deprecate MAKE-PATHNAME and the PATHNAME-xxx accessors and leave the question of representation of components unspecified in the standard.
I realize that this position may be seen as being too extreme. In that case I'd be willing to shut up and go along with proposal SPECIFY as long as my position gets noted in the writeup.
Larry Masinter and Dave Moon both feel that we should be able to prescribe exact pathname component values for popular file systems, so that multiple implementations will behave the same way when using the same file system. Obvious candidates as the key file systems are MS/DOS, Macintosh, Unix, and VAX/VMS. A call for volunteers to write up tables for any of them produced absolutely no response, however.