[Openmcl-devel] Thread-local bindings

[Rainer Joswig]

If a variable is used in a function and there is no special declaration and there is no DEFVAR, then the binding is lexical.

DEFVAR declares a variable to be special.

Then ALL new code on all levels (all lets, lambda vars, ...) will use dynamic binding.



> Am 14.06.2019 um 16:16 schrieb martin <brooks.martin at sympatico.ca>:
> 
> Hello All
> 
> I am confused about the semantics of thread-local bindings when using process-run-function. 
> CCL version: Clozure Common Lisp Version 1.12-dev (v1.12-dev.4-3-gdd5622e9) DarwinX8664
> 
> Suppose that the variable foo is not globally bound:
> 
> ? foo
> > Error: Unbound variable: FOO
> 
> Consider the following form:
> 
> (process-run-function :process1 
>   #'(lambda ()
>       (let ((foo 2))
>         (flet ((bar () (print foo) :return-me-from-foo))
>           (bar)
>           (process-run-function :process2 #'bar)
>           :return-me-from-lambda))))
> 
> The result is to print 2 twice:
> 
> 2 
> 2 
> 
> Neither keyword return value appears, nor should they — I put them in the code to disambiguate printing from the value returned by print.
> 
> Now bind foo at top level.
> 
> ? (defvar foo 3)
> FOO
> 
> Execute the form again, to get these to print results:
> 
> 2 
> 3 
> 
> My confusion: 
> The second result (print 2 & 3) demonstrates my understanding of thread-local bindings.
> The first result (print 2 & 2) seems wrong — why didn’t Lisp complain that foo was unbound in the call to bar within :process2 ?

Because FOO uses the lexical binding introduced by the LET.

> 
> My confusion gets worse — restart Lisp, so that foo is not globally bound, and do the same tests with the following form, to see it print 4 & 4.
> 
> (let ((foo 4))
>   (process-run-function :process1 
>     #'(lambda ()
>         (flet ((bar () (print foo) :return-me-from-foo))
>           (bar)
>           (process-run-function :process2 #'bar)
>           :return-me-from-lambda))))
> 
> 4 
> 4 
> 


lexical binding


> And now globally bind foo:
> 
> ? (defvar foo 5)
> FOO


> 
> The form now prints 5 & 5 .
> 
> 5 
> 5
> 

dynamic binding


> Help! What’s the rule?!?
> 
> Furthermore, I take it that stack-local bindings apply to variables only, not functions.
> To test this, I gave bar a global definition:
> 
> (defun bar () (print 27))
> 
> But this did not change the above results; in other words, the local definition was used in both threads.
> 
> All consolation gratefully accepted,
> Martin
> 
> 
> 
> 
> 
> 
> _______________________________________________
> Openmcl-devel mailing list
> Openmcl-devel at clozure.com
> https://lists.clozure.com/mailman/listinfo/openmcl-devel

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.clozure.com/pipermail/openmcl-devel/attachments/20190614/5f84c31e/attachment.htm>