🚀 go-pugleaf

>This is not exactly a novel idea.
Never claimed it was new.  The original poster asked for a notation.

> The problem with segment
>variables is that unification not only may have several solutions, but
>occasionally infinitely many of them.  Consider:
>
>        [..X foo] to be unified with [foo ..Y]
>
>The set of unifiers for this example is:
>
>        { X = Y = [] }
>        { X = Y = [foo] }
>       { X = Y = [foo foo] }
>        { X = Y = [foo foo foo] }
>        ...

Actually, [..X, foo] unified with [foo, ..Y] would yield
	X = Y = []
	and
	X = [foo, ..A], Y = [..A, foo]
I don't remember the proof offhand, but if neither sequence is
circular, there is always a finite number of unifiers.  The problem
occurs when you try to unify X:[a,..X] with [...,E,...] (infinitely
many unifiers) or [...,L] (no unifiers, but it's hard to prove that).  

Evan Kirshenbaum
    HP Laboratories
    3500 Deer Creek Road, Building 26U
    Palo Alto, CA  94304

    kirshenbaum@hplabs.hp.com
    (415)857-7572