From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: arthur miller Newsgroups: gmane.emacs.devel Subject: Sv: Is this a bug in while-let or do I missunderstand it? 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List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Original-Sender: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.emacs.devel:325338 Archived-At: --_000_DU2PR02MB10109F4094C90A796CD77B809965E2DU2PR02MB10109eu_ Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable >> >> (progn >> >> (while-let ((run t)) >> >> (message "Running") >> >> (setf run nil)) >> >> (message "out of loop")) >> >> >> >> It ends in infinite recursion. setf/setq have no effect on the lexica= l variable. >> > >> >Probably not infinite recursion but infinite loop. >> > >> >Why would you expect anything else? =91while-let=92 is documented as: >> > >> > Bind variables according to SPEC and conditionally evaluate BODY. >> >> What should I expect? >> >> It does not says *read-only bindings*, it says bindings. Is it >> unreasonable to store a value in an established lexical binding? > >I expect the binding is writable *but* it gets re-assigned on each iterati= on. Yes. >> That is what I expect while-let to be equivalent to. > >This is what I expect: > > (progn > (let ((run)) > (while (setf run t) > (message "running") > (setf run nil) ; useless because =91run=92 will be >reassigned right next > ) > (message "not running") ; unreachable > ) > Mnjah; more like this: (catch 'done (while t (let* ((run nil)) (if run (do-body) (throw 'done nil))))) I have already posted the macro expansions in respone to Phillip. It is quite clear what is going on. I think it is a bug, or at least very unintuitive behaviour. But the worst, we can see that the claimed optimizaiton does not take place at all: (pp (macroexpand-all '(while-let ((run t) (x 'expensive) (y 'more-expensive) (z 'the-most-expensive)) (message "running") (setf run nil)))) (catch 'done1522 (while t (let* ((run (and t t)) (x (and run 'expensive)) (y (and x 'more-expensive= )) (z (and y 'the-most-expensive))) (if z (progn (message "running") (setq run nil)) (throw 'done1522 nil= ))))) Which makes wonder if the convoluted code in subr.el is worth compared to t= he naive implementation I posted. Perhaps someone can pull off the optimizatio= n with some clever macro, I don't know. I think it was enough from me as an outsider to point out the possible bug.= Whether people here wants to poop on it, or acknowledge and fix the bug is not up = to me. In other words, I think I am done here. /best regards ________________________________ Fr=E5n: Yuri Khan Skickat: den 9 november 2024 14:15 Till: arthur miller Kopia: emacs-devel@gnu.org =C4mne: Re: Is this a bug in while-let or do I missunderstand it? On Sat, 9 Nov 2024 at 20:03, arthur miller wrote: > > >> (progn > >> (while-let ((run t)) > >> (message "Running") > >> (setf run nil)) > >> (message "out of loop")) > >> > >> It ends in infinite recursion. setf/setq have no effect on the lexical= variable. > > > >Probably not infinite recursion but infinite loop. > > > >Why would you expect anything else? =91while-let=92 is documented as: > > > > Bind variables according to SPEC and conditionally evaluate BODY. > > What should I expect? > > It does not says *read-only bindings*, it says bindings. Is it > unreasonable to store a value in an established lexical binding? I expect the binding is writable *but* it gets re-assigned on each iteratio= n. > (progn > (let ((run t)) > (while run > (message "running") > (setf run nil)) > (message "not running"))) > > That is what I expect while-let to be equivalent to. This is what I expect: (progn (let ((run)) (while (setf run t) (message "running") (setf run nil) ; useless because =91run=92 will be reassigned right next ) (message "not running") ; unreachable ) --_000_DU2PR02MB10109F4094C90A796CD77B809965E2DU2PR02MB10109eu_ Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable
>> >> (progn
>> >>   (while-let ((run t))
>> >>     (message "Running")
>> >>     (setf run nil))
>> >>   (message "out of loop"))
>> >>
>> >> It ends in infinite recursion. setf/setq have no effect o= n the lexical variable.
>> >
>> >Probably not infinite recursion but infinite loop.
>> >
>> >Why would you expect anything else? =91while-let=92 is documen= ted as:
>> >
>> >    Bind variables according to SPEC and conditional= ly evaluate BODY.
>>
>> What should I expect?
>>
>> It does not says *read-only bindings*, it says bindings. Is it
>> unreasonable to store a value in an established lexical binding?
>
>I expect the binding is writable *but* it gets re-assigned on each iter= ation.

Yes.

>> That is what I expect while-let to be equivalent to.
>
>This is what I expect:
>
>    (progn
>      (let ((run))
>        (while (setf run t)
>          (message "running")
>          (setf run nil)       = ; useless because =91run=92 will be
>reassigned right next
>        )
>      (message "not running")  ; unreacha= ble
>    )
>

Mnjah; more like this:

(catch 'done
  (while t
    (let* ((run nil))
      (if run
          (do-body)
          (throw 'done nil)))))

I have already posted the macro expansions in respone to Phillip.
It is quite clear what is going on. I think it is a bug, or at
least very unintuitive behaviour. But the worst, we can see that the
claimed optimizaiton does not take place at all:

(pp (macroexpand-all
     '(while-let ((run t)
                  (x 'expensiv= e)
                  (y 'more-exp= ensive)
                  (z 'the-most= -expensive))
        (message "running")
        (setf run nil))))

(catch 'done1522
  (while t
    (let*
        ((run (and t t)) (x (and run 'expensive)) (y (a= nd x 'more-expensive))
         (z (and y 'the-most-expensive)))
      (if z (progn (message "running") (setq run n= il)) (throw 'done1522 nil)))))

Which makes wonder if the convoluted code in subr.el is worth compared to t= he
naive implementation I posted. Perhaps someone can pull off the optimizatio= n with
 some clever macro, I don't know. 

I think it was enough from me as an outsider to point out the possible bug.= Whether
 people here wants to poop on it, or acknowledge and fix the bug is no= t up to me. 

In other words, I think I am done here.

/best regards
Fr=E5n: Yuri Khan <yuri.= v.khan@gmail.com>
Skickat: den 9 november 2024 14:15
Till: arthur miller <arthur.miller@live.com>
Kopia: emacs-devel@gnu.org <emacs-devel@gnu.org>
=C4mne: Re: Is this a bug in while-let or do I missunderstand it?
 
On Sat, 9 Nov 2024 at 20:03, arthur miller <art= hur.miller@live.com> wrote:
>
> >> (progn
> >>   (while-let ((run t))
> >>     (message "Running")
> >>     (setf run nil))
> >>   (message "out of loop"))
> >>
> >> It ends in infinite recursion. setf/setq have no effect on th= e lexical variable.
> >
> >Probably not infinite recursion but infinite loop.
> >
> >Why would you expect anything else? =91while-let=92 is documented = as:
> >
> >    Bind variables according to SPEC and conditiona= lly evaluate BODY.
>
> What should I expect?
>
> It does not says *read-only bindings*, it says bindings. Is it
> unreasonable to store a value in an established lexical binding?

I expect the binding is writable *but* it gets re-assigned on each iteratio= n.

> (progn
>   (let ((run t))
>     (while run
>       (message "running")
>       (setf run nil))
>     (message "not running")))
>
> That is what I expect while-let to be equivalent to.

This is what I expect:

    (progn
      (let ((run))
        (while (setf run t)
          (message "runni= ng")
          (setf run nil) =       ; useless because =91run=92 will be
reassigned right next
        )
      (message "not running")  ; un= reachable
    )
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