Re: [racket-users] Looking to trigger the end of a loop by the creation of a file.

[George Neuner]

On 10/2/2021 7:25 PM, Don Green wrote:

Looking to trigger the end of a loop by the creation of a file.
Is this possible? Is this advisable?
Currently using:
a 'for' loop with
a 'for' loop guard expression to test for the existence of a file.
Tried file-exists? but that does not seem appropriate.
Tried using Racket function: filesystem-change-evt but that did not 
seem appropriate.
Is it possible to trigger an end condition on a 'for' loop by the 
creation of a file?
I suspect my problem is that it takes a significant amount of time for 
the operating system to register the creation of a file.
So maybe the best that can be done is to use file-exists? as it works 
but there a many loops of the 'for' loop before the end condition 
takes effect.

Any comments? --


Is the loop doing something else while it waits?  If not, you might as 
well use  filesystem-change-evt.


A polling loop /may/ respond faster than waiting on an event, but at the 
level of user applications that is /not/ guaranteed.  Is there some 
reason you (think you) need to respond very quickly when the file is 
created?


George

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Re: [racket-users] Looking to trigger the end of a loop by the creation of a file.

[Sorawee Porncharoenwase]

What do you mean by "Tried using Racket function: filesystem-change-evt but
that did not seem appropriate."? What's inappropriate about it?

My first thought is to initialize a variable with `#f`. Spawn a thread
before the loop that uses `filesystem-change-evt` so that when the event
that you are interested in occurs, mutate the variable to `#t`. In the
loop, break from the loop when the variable is `#t`.

I guess you can also poll `file-exists?` yourself in the thread, with some
`sleep` between each polling.

Related library: https://github.com/zyrolasting/file-watchers/

On Sat, Oct 2, 2021 at 4:25 PM Don Green  wrote:

> Looking to trigger the end of a loop by the creation of a file.
> Is this possible? Is this advisable?
> Currently using:
> a 'for' loop with
> a 'for' loop guard expression to test for the existence of a file.
> Tried file-exists? but that does not seem appropriate.
> Tried using Racket function: filesystem-change-evt but that did not seem
> appropriate.
> Is it possible to trigger an end condition on a 'for' loop by the creation
> of a file?
> I suspect my problem is that it takes a significant amount of time for the
> operating system to register the creation of a file.
> So maybe the best that can be done is to use file-exists? as it works but
> there a many loops of the 'for' loop before the end condition takes effect.
> Any comments?
>
> --
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> 
> .
>

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[racket-users] Looking to trigger the end of a loop by the creation of a file.

[Don Green]

Looking to trigger the end of a loop by the creation of a file.
Is this possible? Is this advisable?
Currently using: 
a 'for' loop with
a 'for' loop guard expression to test for the existence of a file.
Tried file-exists? but that does not seem appropriate.
Tried using Racket function: filesystem-change-evt but that did not seem 
appropriate.
Is it possible to trigger an end condition on a 'for' loop by the creation 
of a file?
I suspect my problem is that it takes a significant amount of time for the 
operating system to register the creation of a file.
So maybe the best that can be done is to use file-exists? as it works but 
there a many loops of the 'for' loop before the end condition takes effect.
Any comments?

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Re: [racket-users] Racket virtual meet-up in 50 minutes (8pm UTC) TODAY

[Stephen De Gabrielle]

Thank you to everyone who joined us today

I’m looking forward to seeing more of you at the next meet-up:

When: *First Saturday EVERY Month UTC: 20:00* (30 minutes but can overrun)
Calendar: Google

 , iCal


Where: https://gather.town/app/wH1EDG3McffLjrs0/racket-users

The link is free for all - so if you want to organise a meet-up at a time
that is better for your time zone please feel free!

stephen



On Sat, 2 Oct 2021 at 20:09, Stephen De Gabrielle 
wrote:

> All welcome
>
> starts in a little over 50 minutes
>
> Where: https://gather.town/app/wH1EDG3McffLjrs0/racket-users
>
> When: *First Saturday EVERY Month UTC: 20:00* (30 minutes but can overrun)
> Calendar: Google
> 
>  , iCal
> 
>
> stephen
>
> --
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> 
> .
>
-- 


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Re: [racket-users] Re: Escape continuations for fussy code

[jackh...@gmail.com]

Here's my solution:

(define/guard (f x)
  (guard (foo? x) else
#false)
  (define y (bar x))
  (define z (jazz x y))
  (guard (loopy? z) else
#false)
  (define a (yowza z))
  (guard (string? a) else
(error 'ugh))
  (define b (bonkers a))
  (guard (number? (hoop x b)) else
(error 'um))
  (define ...))

It uses a `guard` macro I wrote and talked about in this thread 
.
On Friday, October 1, 2021 at 12:53:25 PM UTC-7 hen...@topoi.pooq.com wrote:

> On Fri, Oct 01, 2021 at 02:32:52PM -0400, David Storrs wrote:
> > On Fri, Oct 1, 2021 at 11:58 AM Hendrik Boom  
> wrote:
> > 
> > > On Fri, Oct 01, 2021 at 02:22:14PM +, Jesse Alama wrote:
> > > > Hello,
> > > >
> > > > Have you ever wished you could do a C-style return in the middle
> > > > of a block of Racket code? When you're in the heat of things with
> > > > a complicated problem where input values need a fair amount of
> > > > multi-stage extraction and validation, using cond quickly pulls
> > > > code to the right. My procedure is:
> > > >
> > > > * cond/case. In each branch:
> > > > * Define some new values safe in the knowledge of where you are
> > > > (extract) and perhaps check them, if necessasry (validate)
> > > > * Make sure you have an else branch.
> > > > * return to 1 and repeat as many times as necessary.
> > > >
> > > > The result:
> > > >
> > > > (cond [(foo? x)
> > > > (define y (bar x))
> > > > (define z (jazz x y))
> > > > (cond [(loopy? z)
> > > > (define a (yowza z))
> > > > (cond [(string? a)
> > > > (define b (bonkers a))
> > > > (cond [(number? (hoop x b))
> > > > (define ...)]
> > > > [else
> > > > (error 'um)])]
> > > > [else
> > > > (error 'ugh)])]
> > > > [else #f])]
> > > > [else #f])
> > >
> > >
> > I'm presuming that this code should either return #f, return a calculated
> > value, or raise an exception. If so, here's a version that runs in plain
> > racket that I find pretty easy to read. It has the advantage that the
> > 'return #f' parts aren't way far away from what causes them.
> > 
> > (with-handlers ([false? identity] ; return #f
> > [any/c raise]) ; re-raise everything else
> > (let* ([x (if (foo? x)
> > x
> > (raise #f))]
> > [z (jazz x (bar x))]
> > [a (if (loopy? z)
> > (yowza z)
> > (raise #f))]
> > [b (if (string? a)
> > (bonkers a)
> > (error 'ugh))])
> > (if (number? (hoop x b))
> > 'all-good
> > (error 'um
>
> Yes. But different semantics if bar, yowza, and bonkers have side effects.
> If they don't, they're quite equivalent.
>
> -- hendrik
>
> > 
> > If instead you want to return the exn that comes from error instead of
> > re-raising it then you can do that by removing the false? clause from the
> > with-handlers. NOTE: You should re-raise exn:break since otherwise the
> > user cannot ^C the program.
> > 
> > (with-handlers ([exn:break? raise]
> > [any/c identity])
> > ...put the let* code here...)
> > 
> > -- 
> > You received this message because you are subscribed to the Google 
> Groups "Racket Users" group.
> > To unsubscribe from this group and stop receiving emails from it, send 
> an email to racket-users...@googlegroups.com.
> > To view this discussion on the web visit 
> https://groups.google.com/d/msgid/racket-users/CAE8gKodxas7jtze%2BttcFA%2BG0ATKUFZD3rhK%2B%3Dn2U1md1zQPJSg%40mail.gmail.com
> .
>

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[racket-users] Racket virtual meet-up in 50 minutes (8pm UTC) TODAY

[Stephen De Gabrielle]

All welcome

starts in a little over 50 minutes

Where: https://gather.town/app/wH1EDG3McffLjrs0/racket-users

When: *First Saturday EVERY Month UTC: 20:00* (30 minutes but can overrun)
Calendar: Google 

 , iCal 


stephen 

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Re: [racket-users] Racket meeting tomorrow?

[Stephen De Gabrielle]

All welcome

starts in a little over 50 minutes

Where: https://gather.town/app/wH1EDG3McffLjrs0/racket-users

When: *First Saturday EVERY Month UTC: 20:00* (30 minutes but can overrun)
Calendar: Google 

 , iCal 


stephen 


On Friday, October 1, 2021 at 8:56:08 PM UTC+1 hen...@topoi.pooq.com wrote:

> On Fri, Oct 01, 2021 at 12:31:27PM -0700, Sam Phillips wrote:
> > October 2, 2021
> > 1 PM PDT
> > 4 PM EDT
> > 8 PM UTC
> > 10 PM CEST
> > 
> > Should be the same URL as previous meetups.
> > 
> > https://gather.town/app/wH1EDG3McffLjrs0/racket-users
>
> I'll try to be there even though I haven't been doing much Racketting 
> lately.
> I didn't see it announced in Racket News, so I asked.
>
> -- hendrik
>
> > 
> > Cheers,
> > Sam
> > 
> > On Fri, Oct 1, 2021 at 9:49 AM Hendrik Boom  
> wrote:
> > >
> > > Is there going to be a Racket online meeting at the gather site 
> tomorrow
> > > on October 2? There have been on previous
> > > first-Saturdays-in-the-month.If so, at what time, and what's the URL?
> > >
> > > -- hendrik
> > >
> > > --
> > > You received this message because you are subscribed to the Google 
> Groups "Racket Users" group.
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> an email to racket-users...@googlegroups.com.
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> https://groups.google.com/d/msgid/racket-users/20211001164939.xrugfg7xlkj4pmfo%40topoi.pooq.com
> .
> > 
> > -- 
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> .
>

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