[r6rs-discuss] [Formal] Formal semantics should not contain complicating optimizations

[AndrevanTonder]

On Fri, 16 Mar 2007, Robby Findler wrote:

> Okay, sure. You've said that several times now. I agree (for the
> second time): the semantics cannot be used to reason about space
> behavior!
>
> You also stated that the semantics gets sharing wrong. If all you mean
> is the below, then I understand what you mean there is nothing more to
> say, as far as I'm concerned.
>
> But, just in an attempt to be clear to you, I'm claiming that there is
> no observable way in which sharing is wrong.

Except for the incomplete implementation of EQV? on procedures, which you have 
said is not technically wrong, but presumably can be observed not to give the 
correct answer ;-)

But okay, I'll drop the space behaviour issue for now, given that it is 
apparently and unfortunately not a design goal of the editors, after one final 
remark:  You could easily get a semantics with the space and sharing 
behaviour that is implied by the discussion on procedure location tags and eqv? 
by a very small modification whereby user procedure parameters are put in the 
store (as pairs currently are) rather than substituted directly.  Scalar values 
and primitives could still be substituted directly, so the readability of many 
simple reduction sequences would not be affected.

Given that this seems to be a trivial modification, I think 
an implementation in which this behaviour is provided as an option would be 
an easy thing to make available.  It would be valuable to those of us who are 
interested in reasoning about space.

Andre