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Re: perhaps I've missed something ...



John Clements <clements@xxxxxxxxxxx> writes:

> You believe that an "economy of concepts" may be achieved by merging
> set!  and set-car!.  I believe that this is fundamentally misleading.

To clarify:  I don't think merging set! and set-car! *per se*
leads to "economy of concepts".  However, it may be a more economical
way to *organize* the concepts.

Alternatively, one can argue it requires one big new concept
"location" (or lvalue if you prefer) (which is implicit in the
semantics anyway); once you have that concept, it unifies or
simplifies a lot of getter/setter pairs, which leads to fewer concepts
*total*.

I don't think it makes much difference either way formally.
The question is which style is more natural in practical use
I can see this is largely a matter of taste and personal preference.
And a matter of different cultures.

> If this were the case, then set! could presumably operate on any 
> environment, and not simply the current one.

I was trying to make the point that the two forms of set! are
related, not give the semantics of anything.

> I claim that rather than a first-class entity, the environment is 
> more or less an implementation detail; the clearest model to use in 
> teaching programming is that of algebra, and application by 
> substitution.

Except the top-level environment, which R5RS at least suggests (but
does not require) be a first-class entity.
-- 
	--Per Bothner
per@xxxxxxxxxxx   http://www.bothner.com/~per/