mapping files to objects

cwg@DeepEddy.Com cwg@DeepEddy.Com
Tue, 06 May 1997 11:40:11 -0500

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In the interest of getting something that is (a) implementable on top of the 
Unix file system and (b) has semantics that can be expanded to The Right 
Thing (tm) later, I'd like to make a modest proposal (no, we aren't going to 
eat our young).

1) Let's take the CL path objects and add the notion of a file type to the 
object.  This file type would *not* appear in the printed representation of 
the path, but would instead by set and read by accessor functions.  This type 
could then be mapped into a MIME type or a MacOS style owner/type pair.  
Initially, I thought it should be a MIME type, but then my stupidity passed 
and I realized that it should be a CLOS class.  *duh*.  This class would have 
a method for determining the MIME type or any other foreign typing system 

2) Since a Unix file system doesn't have these semantics in it, let's define a 
facility which allows one to define mappings between Unix paths and the above 
defined classes.  A similar facility should be defined between MIME types and 

(def-unix-extension-map "tar"
   :class 'tarball)
(def-mime-type-map "application/x-tar"
   :class 'tarball)
(def-unix-directory-map "/var/spool/mail"
   :contains-class 'mbox)
(def-unix-filename-map "README"
   :class 'text-file)
(def-unix-extension-map "lisp"
   :class 'lisp-source-code)

lisp-source-code and mbox are probably built on text-file with additional 
methods for handling lisp source and the broken Unix mailfile format.

3) It now becomes nearly trivial to write the function that I previously 
proposed to map from a pathname to an object representing that file.

4) When/if we write our own file system, this can be implemented natively so 
that all files would have a class associated with them.  Our file system 
wouldn't need real extensions so we'd do away with that baggage, but it should 
still support some form of soft deletion and versioning.

5) Even if we never develop a working Object-Oriented store, we're already 
well ahead of the rest of the universe in our file type information (and, most 
importantly, it gives me the hooks that I want to start writing a 
well-integrated mail system).



Chris Garrigues                    O-              cwg@DeepEddy.Com
  Deep Eddy Internet Consulting                     +1 512 432 4046
  609 Deep Eddy Avenue
  Austin, TX  78703-4513              http://www.DeepEddy.Com/~cwg/

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