[pro] couple questions about dynamic bindings

[Greg Gilley]

Nope, that was it. I had thought progv would treat the binding with no argument like a free binding. Instead, it explicitly unbinds the variable.

Thanks!

	Greg

On Dec 27, 2010, at 8:43 AM, Peter Seibel wrote:

> I'm assuming you're surprised by the results of the forms you give
> below. The issue isn't that progv makes "a differest special"--it
> makes a new binding. So in the first form you've created a new binding
> for x with no supplied value so boundp returning NIL seems about
> right. And in the second case, you create a binding, assign it a
> value, and then leave the scope of the binding. Or I'm missing
> something about your question.
> 
> -Peter
> 
> On Sun, Dec 26, 2010 at 4:04 PM, Greg Gilley <ggilley at gerg.org> wrote:
>> 
>> There are some tests in the common-lisp test suite with dynamic binding that I don't understand. If someone could help shed some light on them I'd appreciate it.
>> 
>> progv makes it's arguments special. I don't understand how they can be a different special than the one declared in the let. I'd love an explanation.
>> 
>> (let ((x 0))
>>    (declare (special x))
>>    (progv '(x) ()
>>      (boundp 'x))) ==> NIL
>> 
>> (let ((x 0))
>>    (declare (special x))
>>    (progv '(x) () (setq x 1))
>>    x) ==> 0
>> 
>> Thanks,
>> 
>>        Greg
>> 
>> 
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>> 
> 
> 
> 
> -- 
> Peter Seibel
> http://www.codequarterly.com/