[mercury-users] Unique and mostly-unique modes

[David Overton]

On Thu, Sep 08, 2005 at 02:35:48PM +1000, Ralph Becket wrote:
> > test.m:018: In clause for `write(in, di, uo)':
> > test.m:018:   mode error: argument 3 did not get sufficiently instantiated.
> > test.m:018:   Final instantiatedness of `HeadVar__3' was
> > test.m:018:   `unique(test.socket(ground))',
> > test.m:018:   expected final instantiatedness was `unique'.
> > 
> > How is this incorrect? Surely unique(socket(ground)) <= unique.
> 
> Indeed.

This one has been correctly identified by the compiler as a mode error.
The argument to socket/1 is not unique because it is also returned as
the first argument of read/3 and so there is more than one live
reference to it.  The inst `unique' means unique all the way down.

David
-- 
David Overton
WWW: http://www.overtons.id.au/
Mobile Phone (UK): +44 7799 344 322
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