Mostly unique

[Peter Schachte]

Is there a difference between mostly unique input and unique input?
As far as I can see, a promise not to copy a pointer to any part of a
term should not depend on how many solutions that predicate has, so I
would argue there isn't a difference.  The problem with multiple
solutions comes up when one wants to destructively modify something,
which requires both deadness and uniqueness.

This then raises the question: is there a useful difference between
the unique and mostly unique insts?  I'm not as sure about this, but I
don't see this difference either.  If there isn't a meaningful
difference, I think it would be a good thing to remove that
distinction from the language.


-- 
Peter Schachte                | PL/1, "the fatal disease", belongs more to
mailto:pets at cs.mu.OZ.AU       | the problem set than to the solution set.
http://www.cs.mu.oz.au/~pets/ |     -- E. W. Dijkstra 
PGP: finger pets at 128.250.37.3 |