Need for XString?

I was wondering if there was any interest in an XString library, the basis 
of which I've attached (it needs to be cleaned up, documented, given a mli 
file, etc).  Basically, it's an unbalanced tree of strings.  This allows 
concatenation in strict O(1), and to_string in O(n) (n being the number of 
characters in the string).

On the other hand, a lot of it's functionality is taken up by the standard 
library Buffer (which I discovered after writting the above).

If there is interest, I'll clean it up and check it in.  If not, I'm going 
to delete it.

Brian

xstr.ml
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