Issue: PATHNAME-SYSTEM-TYPE (version 1)

[David A. Moon <Moon@STONY-BROOK.SCRC.Symbolics.COM>]

This is a new issue.  It arose from an investigation of features
that are plausibly needed but missing from draft ANSI Common Lisp.
This issue seems sufficiently simple and noncontroversial that
I would like to see it on the agenda for the June X3J13 meeting.
Let's use the cleanup subcommittee to test the assertion that this
is a simple and noncontroversial issue.  If it's controversial,
let's just drop it, otherwise let's give X3J13 a chance to vote
for or against it.

Issue:          PATHNAME-SYSTEM-TYPE
References:     Internet RFC 1010, pages 24-25
Related issues: PATHNAME-LOGICAL
Category:       ADDITION
Edit history:   23-May-89, Version 1 by Moon

Problem description:

  It is sometimes necessary to write nonportable pathname manipulation code
  that performs operations specific to individual file systems.  Sometimes
  this is to get around inadequacies of the Common Lisp pathname model,
  sometimes it is to take advantage of idiosyncratic features of a
  particular file system.  Common Lisp does not provide any way to ask what
  file system a pathname is for, so there is no good way for this type of
  pathname manipulation code to be sure what file system it is dealing
  with.  Sometimes it can tell by checking what Lisp implementation it is
  running in, but as more and more implementations support network file
  access, this is becoming less reliable.

Proposal (PATHNAME-SYSTEM-TYPE:ADD-FUNCTION):

  Add the following function:

    PATHNAME-SYSTEM-TYPE pathname                               [Function]

    Coerce the pathname argument to a pathname, signalling an error of type
    TYPE-ERROR if the argument is not a pathname, string, or file stream.
    Return a keyword symbol that identifies the type of file system this
    pathname is for.  The names of these symbols are derived from the
    system type names used by the Internet Domain Name system, listed in
    the referenced document.  Implementations that use a file system listed
    in that document, or superseding documents, should return a symbol in
    the keyword package whose name comes from that document.  Examples:

        :MSDOS          MS/DOS or PC/DOS
        :TOPS10         TOPS-10
        :TOPS20         TOPS-20 
        :ULTRIX         Ultrix
        :UNIX           Unix with long file names (4.2 or newer)
        :VM/370         VM/370
        :VMS            VAX/VMS with long file names (version 4.4 or newer)
        :XENIX          Xenix

    The following additional symbols are specified by Common Lisp:

        :LOGICAL        logical pathname (see issue PATHNAME-LOGICAL)
        :UNIX-14        Unix with 14-character file name limit
        :VMS-9          VAX/VMS with 9-character file name limit
        NIL             system type cannot be determined

    For file systems not named in the referenced document, implementations
    should make up a name consistent with the spelling conventions defined
    in that document.

Examples:

  ;; On a non-networked IBM PC:
  (PATHNAME-SYSTEM-TYPE (USER-HOMEDIR-PATHNAME)) => :MSDOS

Rationale:

  PATHNAME-SYSTEM-TYPE gives a nonportable pathname manipulation program
  the basic information it needs to interpret namestrings and manipulate
  pathname components.

Current practice:

  Symbolics Genera has had a similar feature under a different name
  for many years.  A few of the keyword symbols returned by Genera
  are spelled differently, merely for historical reasons.

Cost to Implementors:

  Trivial.

Cost to Users:

  None.

Cost of non-adoption:

  Implementation-dependent kludges will have to be used.

Performance impact:

  None.

Benefits:

  Improved esthetics.

Esthetics:

  Implementation-dependent kludges will not have to be used.

Discussion:

  None.