Path: utzoo!attcan!uunet!willett!ForthNet
From: ForthNet@willett.UUCP (ForthNet articles from GEnie)
Newsgroups: comp.lang.forth
Subject: Data Structures
Message-ID: <673.UUL1.3#5129@willett.UUCP>
Date: 18 Mar 90 00:23:25 GMT
Organization: Latest link in the ForthNet chain.  (Pgh, PA)
Lines: 46


 Date: 03-13-90 (09:54)              Number: 3035 (Echo)
   To: ALL                           Refer#: NONE
 From: JONAH THOMAS                    Read: (N/A)
 Subj: B-TREES                       Status: PUBLIC MESSAGE

    Some months ago Dave Weinstein put up a message about using TREE
 structures, following a concept by Larry Forsley.  There was a defining
 word, TREE , which recursively made each word it defined to also be a
 defining word which did the same thing TREE did.  Each word got tagged
 with the address of the word which defined it, which created a
 tree-like hierarchy.  Then he defined a set of words which looked at
 the tags to trace out the 'lineage' of any particular word.  It was
 based on an idea by Larry Forsley.  It looked neat, so I saved it.
    When I needed it, I was a bit disappointed.  It's a really nice
 idea, but it doesn't actually do much.  Each word in the tree is a
 defining word.  You use it to define 'branches', the later words in the
 tree.  Each of THEM is ALSO a defining word, which can define new
 defining words.  But none of the words can do anything except define
 new defining words, so you need to fiddle with them to actually use
 them for anything.

    The obvious way to do it is to use a non-recursive defining word,
 which would then be used something like:

 0 subs car
      car subs ford
      car subs chevy
      car subs mercedes
          ford subs escort
          chevy subs nova
                nova subs 1987

    Then CHILD could give its pfa, which contains the pfa of PARENT.
 All nice and neat to use, just an extra word when you define a branch.

 : SUBS CREATE , ;
 : .NAMER BODY> >NAME .NAME ;  ( For Pygmy, 3 - .ID )
 : ANCESTRY BEGIN @ ?DUP WHILE DUP .NAMER REPEAT ;
 ---
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