[m-rev.] For review: more fixes to impurity

[Fergus Henderson]

On 18-Nov-2005, Ralph Becket <rafe at cs.mu.OZ.AU> wrote:
> --- doc/reference_manual.texi	16 Nov 2005 07:02:00 -0000	1.337
...
> +Any call or unification goal containing a non-local variable with inst any that

I suggest s/inst any/inst @samp{any}/

> +appears in a negated context (i.e., in a negation or the condition of an
> +if-then-else goal) must be given an @code{impure} annotation because it may
> +violate referential transparency.

I suggest adding

 This is because Mercury
 implements negation using the standard negation-as-failure approach,
 which is not sound if the negated goal binds any non-local variables.

-- 
Fergus Henderson                    |  "I have always known that the pursuit
                                    |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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