🚀 go-pugleaf

I would like to add a well-formed substring table mechanism to
my NL parser.  The parser is of the standard top-down left-to-right 
backtracking sort.  The obvious implementation is to assert the
substrings.  Because the parse tree fragments that I will be saving
will be rather extremely large, I would like to do better than this
if at all possible.  I have a few ideas, but I do not know how to
implement them.

1.  Does it make sense to store the substrings for every nonterminal,
    or perhaps only for certain nonterminals (noun phrase and clause)?
2.  Is it possible to have one saved substring point to another
    to use structure sharing?
3.  Should I save only successful substrings, or failed substrings also?


Thanks in advance,
John Dowding

dowding@prc.unisys.com