Property lists in MIT Scheme. 
Author Message
 Property lists in MIT Scheme.

   Date: 15 Dec 90 07:54:21 GMT
   From: Michael Richardson <snorkelwacker.mit.edu!apple!julius.cs.uiuc.edu!zaphod.mps.ohio-state.edu!v

     Now that exams have started, I've got around to compiling
   MIT Scheme (6.1.2, Microcode 10.2, runtime 13.91, sf 3.13). I
   discovered to my amu{*filter*}t that property lists seem to be absent.
   Okay, I says, is assq a primitive? Seems to be. No problem.

Property lists are available in MIT Scheme, with slightly different
names:

    putprop             2d-put!
    getprop             2d-get
    remprop             2d-remove!

The names were changed because these property lists differ in some
important respects from those of Lisp:

* The keys can both be any object -- it not necessary that one be a
  symbol.

* The keys are not protected from garbage collection -- if one of the
  keys is reclaimed, the property is automatically removed from the
  table.

* The performance is somewhat worse -- two linear-time lookups instead
  of one.

     While grep'ing through the runtime code and microcode for
   references to property lists, I noticed a bunch of stuff on hash
   functions, etc... Is there, (already existing?) some code to do
   property list-like things using hash codes?

The hash-code stuff is used for hash tables, not property lists.

     I've read R^3S (quite awhile ago), but haven't haven't gotten
   TeX up so I can print off the R^4S included in the docs. There is
   a hacked up copy of one of them (I don't remember which) with the
   TI-Scheme 'manuals' in the CS labs. They actually don't mention
   property lists at all (that I remember).
     Were property lists dropped in scheme? Why?

Property lists were never part of the Scheme reports.

     On a somewhat related note --- I believe that there is a 6.2
   MIT Scheme no? Has anyone implemented the rational types? Does
   6.2 have them?

6.2 doesn't have rationals.  Release 7.1, entering beta test in a few
days, does.

      :!mcr!:            |    The postmaster never          |  So much mail,
      Michael Richardson |            resolves twice.       |  so few cycles.

       - Pay attention only to _MY_ opinions. -         registration in progress.



Tue, 15 Jun 1993 23:23:20 GMT  
 
 [ 1 post ] 

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