Lists, ArgLists, Functors.


    I have been considering a new form for lists. Because of the
    bugs in the current list stuff (reference counting is buggy)
    and that the most common operation on a list is cdr(), I have
    decided that a change to the list structure might be in order.

    This would also allow no CArg's to be reference counted, if
    Functors were changed as well.  This would simplify things
    significantly for CArg's, and probably speed things up as well.


From flisakow Wed Jan  3 17:48:40 1996
To: raghu@cs
Date: Wed, 3 Jan 1996 17:48:40 -0600 (CST)

    I added the "sort" option to write_table, I was going to look through
    the other commands for I/O and see if any others would benefit from
    its use as well.   I only did a fast hack to add it in, so the relation
    to be sorted must already exist (not a derived relation), I think 
    this would be good enough for most uses, as the := operator can be
    used in the other cases.

    The big speedup that was gained from string reference counting has
    made me reconsider some of the earlier decisions I made about CArg.
    The major thing I'm unhappy with is how I did the reference counting
    for functors and lists.  Basically, the way it is now is slowing
    down all the deletion of any type of CArg with an extra function call
    (to destroy, which usually calls delete).

    My plan is to push the reference-counting down a level, (to ArgList
    for Functors) and redesigning the list type to work with this more
    closely.  Examining the operations most heavily performed on lists
    (in Unify) makes it apparent that "cdr" is the most important one.

    My plan (mostly implemented, but still being debugged) is to change
    the list structure to be:

        CArg:
          length of this list
          pointer to list data

        The list data will be stored backwards in a CArgStack (a dynamic
        array that is what the parser uses while reading in arglists and
        lists).  This item is what will be reference counted.  

    A quick example would probably illuminate what I'm trying to say.

    Suppose we have a list, [1,2,3] and have obtained its cdr, [2,3]:

    [1,2,3]:
    CArg (list-type, length 4, "mylist data")

    [2,3]:
    CArg (list-type, length 3, "mylist data")

    mylist data: (nil, 3, 2, 1)  (with a reference count of 2)
   
    Shaun 
-- 
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  Shaun Flisakowski 

  Associate Researcher / Coral DB Programmer   flisakow@cs.wisc.edu
  Computer Science Dept, UW-Madison

  Occam's razor is so sharp - I bought the whole argument.

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