string functions

[Chris Riesbeck <Riesbeck at YALE>]

It seems to be agreed that T will need some decent string functions
and top on my list is a substring function.  UCILisp has one which
I like a lot:

    (SUBSTRING string m n)

takes a substring of string from m to n.  Note that this is not
interpreted as taking n characters starting from position m.  UCILisp
used to do that, and it loses.  But even better is that UCILisp allows
m and n to be negative, in which case they count from the right.  The
most common use of this is

    (SUBSTRING string 1 -1)

which strips off the last character.  Us natural language-hackers really
appreciate that.  Without it, you are constantly grabbing the string
length so you can decrement it.

The problem?  This conflicts with 0-based indexing, unless you allow
-0 to be different than 0, a bag of worms I assume no one wants to
open.

A solution?  Abandon 0-based for substring -- the -1 feature is just
too useful.

Any other ideas?
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