This is not an "optimization" in the usual sense of the word (altho
one could make a case it is a cognitive optimization. Those seem good,
however).
The rule is split like that to avoid complicating the semantics when
no assignments happen. The overall goal is to make it easier to follow
along with a reduction sequence and a simple substitution is easier to
follow along with than putting the variable into the store and taking
it back out again. At least it is in my experience.
Robby
On 3/14/07, AndrevanTonder <andre_at_het.brown.edu> wrote:
> ---
> This message is a formal comment which was submitted to formal-comment_at_r6rs.org, following the requirements described at: http://www.r6rs.org/process.html
> ---
> Name : Andre van Tonder
> Email : andre at het.brown.edu
> Type : simplification
> Priority : low
> Component : Formal semantics
> Version : 5.92
> Pages : 61-73
> Dependencies: None
>
> Summary:
> --------
>
> The current formal semantics contains at least one, and possibly
> more, unnecessary performance optimizations that complicate it rather more than
> necessary. Such optimizations have no place in a formal description of the
> semantics and should be removed.
>
> Description:
> ------------
>
> An example of such an optimization occurs on pages 69 and 70, where procedure
> parameters are treated differently depending on whether they are the target
> of set! in the body of the procedure. This is unnecessary. It clashes with
> the informal description in the body of the report, and it complicates
> the semantics with an unnecessary rule [6appN], and an unnecessary variable
> assigment metafunction that takes about 25 lines (more than half of page 70) to
> describe. Both of these, and possibly other rules depending on this
> distinction, should be removed.
>
> This is one unnecessary complication, presumably based on optimization
> considerations, that I noticed. A more careful reading may turn up other
> optimization-related complications. This formal comment is intended to apply
> to all cases where the formal semantics may be simplified by discarding
> optimizations.
>
>
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Received on Thu Mar 15 2007 - 08:49:17 UTC