Re: Elisp lexical-let

[Daniel Kraft <d@domob.eu>]

Hi,

thanks for your comments; I'm still a bit confused, though :$

Marijn Schouten (hkBst) wrote:
>> What's about this:
>>
>> (defun test () a)
>> (let ((a 1))
>>   (print a) ; 1
>>   (print (test)) ; 1
>>   (lexical-set! a 2)
> there is only one variable `a' in my mental model,
> so this changes the value of the only `a' and all
> subsequent expressions accessing `a' are thus affected.
> The same as if you had written `(set! a 2)'. Dynamic
> and lexical only differ in how free variables in
> procedures are bound.
>>   (print a) ; 1?
> no, (print a) => 2
>>   (print (test)) ; 1
> no, there is only one `a' and its value is 2 here
>>   (print (lexical a)) ; 2
>>   )

Hm...  my problem is trying to understand how you want this implemented; 
my main point about lexical scoping is that it enables us to use Guile's 
built-in lexical mechanisms and we don't have to save the value 
explicitly into some fluids.

But if you require that the second (print (test)) above prints 1 even 
though we have done (lexical-set! a) this means that lexical-set! must 
update the place somehow where a is accessed dynamically (as is done in 
test).  And that seems to imply that this lexical-set! updates the 
fluids, even though it is meant to perform on a lexically bound variable 
a; just in case that "the one" a is at some place referred to dynamically.

>> I don't think it's good to have to "completely seperate" variables a and
>> (lexical a).
> 
> I don't understand what you mean. My proposal is to have one kind of variable
> and two kinds of access.

Can you please elaborate on this?  If there's only one variable and only 
the value 2 after the lexical-set! above (both for (print a) in the 
lexical scope and (print (test)) which accesses a dynamically), what 
would then be the point of writing 'a' or '(lexical a)' and what would 
be the difference between those two?

Yours,
Daniel

-- 
Done:  Arc-Bar-Cav-Ran-Rog-Sam-Tou-Val-Wiz
To go: Hea-Kni-Mon-Pri