[m-rev.] for review: unification expressions

[Simon Taylor]

On 05-Dec-2001, Fergus Henderson <fjh at cs.mu.OZ.AU> wrote:
> On 04-Dec-2001, Simon Taylor <stayl at cs.mu.OZ.AU> wrote:
> > > +The operational semantics of an expression @w{@code{X @@ Y}}
> > > +is that the expression is replaced by a fresh variable @var{Z}, and
> > > +immediately after @var{Z} is evaluated, the conjunction
> > > + at w{@code{Z = X, Z = Y}} is evaluated.
> 
> This is not a completely correct statement;
> it is wrong in the case when mode reordering occurs
> or when the --strict-sequential option is not enabled.
> 
> The first part could be fixed by mentioning that this ordering
> is subject to mode reordering (and then you'd better insert a
> parenthetical cross-references to the section which describes
> mode reordering, i.e. the Semantics chapter).
> 
> You could fix the second part by saying "The ``strict sequential''
> operational semantics (@pxref{Semantics})" instead of "The operation
> semantics".  Although the use of a term defined later in this way
> is not ideal; maybe you can think of something better.

I've changed that paragraph to:

	The strict sequential operational semantics (@pxref{Semantics}) of an
	expression @w{@code{X @@ Y}} is that the expression is replaced by a
	fresh variable @var{Z}, and immediately after @var{Z} is evaluated,
	the conjunction @w{@code{Z = X, Z = Y}} is evaluated.  

The reference to the strict sequential semantics makes any discussion
of mode reordering redundant.
 
> Maybe it would be better to move this text into the Semantics chapter?

I looked at doing that, but it doesn't really fit in well there.
To make it fit there would need to be a discussion of the process
of flattening unifications (to show where the conjunction mentioned
above is inserted into the sequence of atomic unifications). That
might be a good idea, but not as part of this change.

Simon.
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