Asp Forum - Re: [ANN] lazy.rb 0.9.5 -- transparent futures!

Daniel Sheppard

2/22/2006 11:45:00 PM

You can just do

table_name = "CUSTOMERS"
x = promise { table_name }
puts x
=> "CUSTOMERS"

though you have to then make sure that you leave that table_name
variable alone.

table_name = "CUSTOMERS"
x = promise { table_name }
table_name = "MONKEYS"
puts x
=> "MONKEYS"

________________________________

From: Shashank Date [mailto:shanko_date@yahoo.com]
Sent: Thursday, 23 February 2006 9:15 AM
To: ruby-talk ML
Cc: mental@rydia.net
Subject: Re: [ANN] lazy.rb 0.9.5 -- transparent futures!

Hi,

I have a feature request (along with a quick-hack solution).

Please ignore if this is already done or sounds crazy. :-)

Problem: All the promises I make, cannot have any arguments ! !

So something like this is what I have in mind:

x = promise("CUSTOMERS") { |table_name|
long_running_query(table_name)}

Admitedly, in this one-liner it does not make much sense. But if
the block had many many lines of code and referred to the block variable
at multiple places, suddenly it would be mean more to me.

I have attached my hackish solution without really thinking all
the way thru.
Thanks,

-- Shashank

MenTaLguY <mental@rydia.net> wrote:
I'd like to announce a new version of lazy.rb -- this one
offering
thread safety and transparent futures!

Here's the web site, complete with gem and tarball downloads,
plus a bit
of documentation:

http://moonbase.rydia.net/softwar...

Bug reports would be very, very welcome.

________________________________

Yahoo! Mail
Use Photomail
<http://pa....*http://us.rd.yahoo.com/...*http://photomail
mail.yahoo.com> to share photos without annoying attachments.

6 Answers

Daniel Nugent

2/23/2006 1:14:00 AM

table_name = "CUSTOMERS"
x = promise {table_name.dup}
table_name = "MONKEYS"
puts x
=>"CUSTOMERS"

Would avoid the problem. Though it's good to point out that you
likely want to avoid changing the state of any variable that's
captured by a promise closure (unless of course you plan on exploiting
just that).

On 2/22/06, Daniel Sheppard <daniels@pronto.com.au> wrote:
> You can just do
>
> table_name = "CUSTOMERS"
> x = promise { table_name }
> puts x
> => "CUSTOMERS"
>
> though you have to then make sure that you leave that table_name
> variable alone.
>
> table_name = "CUSTOMERS"
> x = promise { table_name }
> table_name = "MONKEYS"
> puts x
> => "MONKEYS"
>
>
> ________________________________
>
> From: Shashank Date [mailto:shanko_date@yahoo.com]
> Sent: Thursday, 23 February 2006 9:15 AM
> To: ruby-talk ML
> Cc: mental@rydia.net
> Subject: Re: [ANN] lazy.rb 0.9.5 -- transparent futures!
>
>
> Hi,
>
> I have a feature request (along with a quick-hack solution).
>
> Please ignore if this is already done or sounds crazy. :-)
>
> Problem: All the promises I make, cannot have any arguments ! !
>
> So something like this is what I have in mind:
>
> x = promise("CUSTOMERS") { |table_name|
> long_running_query(table_name)}
>
> Admitedly, in this one-liner it does not make much sense. But if
> the block had many many lines of code and referred to the block variable
> at multiple places, suddenly it would be mean more to me.
>
> I have attached my hackish solution without really thinking all
> the way thru.
> Thanks,
>
> -- Shashank
>
>
> MenTaLguY <mental@rydia.net> wrote:
> I'd like to announce a new version of lazy.rb -- this one
> offering
> thread safety and transparent futures!
>
> Here's the web site, complete with gem and tarball downloads,
> plus a bit
> of documentation:
>
> http://moonbase.rydia.net/softwar...
>
> Bug reports would be very, very welcome.
>
>
>
>
> ________________________________
>
> Yahoo! Mail
> Use Photomail
> <http://pa....*http://us.rd.yahoo.com/...*http://photomail
> .mail.yahoo.com> to share photos without annoying attachments.
>
>
>

--
-Dan Nugent

Shashank Date

2/23/2006 3:58:00 AM

Hi,

Daniel Nugent <nugend@gmail.com> wrote: table_name = "CUSTOMERS"
x = promise {table_name.dup}
table_name = "MONKEYS"
puts x
=>"CUSTOMERS"

Would avoid the problem. Though it's good to point out that you
likely want to avoid changing the state of any variable that's
captured by a promise closure (unless of course you plan on exploiting
just that).

All this being said, is there any merit in the idea of passing block parameters? I was toying with it briefly and decided to give it a shot on a whim. Will try and come up with a more convincing answer.

Thanks for all your inputs.
-- shanko

---------------------------------
Brings words and photos together (easily) with
PhotoMail - it's free and works with Yahoo! Mail.

Daniel Nugent

2/23/2006 4:22:00 AM

Unlikely. The variables passed into the promise would still have
their references to the outside. You get exactly the same effect as
capturing the variables in a closure and in fact, the given examples
are kinda contrived, it would make more sense to assign CUSTOMERS as a
local variable inside of the promise block, because then it can't be
affected outside of the closure.

However, currently, there IS a block parameter (that of the promise
itself, something to do with circular programming, which sounds
intriguing, but I have hella no idea what it means [PLEASE SEND
LINKS]), but it doesn't seem like you'd use it in most cases.

If you wanted something like, I dunno, currying a promise, you could
just wrap it in a lambda.

On 2/22/06, Shashank Date <shanko_date@yahoo.com> wrote:
> Hi,
>
> Daniel Nugent <nugend@gmail.com> wrote: table_name = "CUSTOMERS"
> x = promise {table_name.dup}
> table_name = "MONKEYS"
> puts x
> =>"CUSTOMERS"
>
> Would avoid the problem. Though it's good to point out that you
> likely want to avoid changing the state of any variable that's
> captured by a promise closure (unless of course you plan on exploiting
> just that).
>
>
>
> All this being said, is there any merit in the idea of passing block parameters? I was toying with it briefly and decided to give it a shot on a whim. Will try and come up with a more convincing answer.
>
> Thanks for all your inputs.
> -- shanko
>
>
> ---------------------------------
> Brings words and photos together (easily) with
> PhotoMail - it's free and works with Yahoo! Mail.
>

--
-Dan Nugent

MenTaLguY

2/23/2006 5:40:00 AM

On Thu, 2006-02-23 at 10:14 +0900, Daniel Nugent wrote:
> table_name = "CUSTOMERS"
> x = promise {table_name.dup}
> table_name = "MONKEYS"
> puts x
> =>"CUSTOMERS"
>
> Would avoid the problem.

Actually, no. String#dup wouldn't get called until the promise was
demanded, by which time table_name refers to a different string.

-mental

MenTaLguY

2/23/2006 5:56:00 AM

On Thu, 2006-02-23 at 13:21 +0900, Daniel Nugent wrote:
> However, currently, there IS a block parameter (that of the promise
> itself, something to do with circular programming, which sounds
> intriguing, but I have hella no idea what it means [PLEASE SEND
> LINKS]), but it doesn't seem like you'd use it in most cases.

Here are a couple trivial examples...

Building a circular data structure (a linked list in this case):

def build_circular_list( *stuff )
promise { |result|
if stuff.empty?
nil
else
list = result
stuff.reverse.each { |thing|
list = [ thing, list ]
}
list
end
}
end

Padding lines of text to a maximum width in a single pass:

def pad_lines( lines )
promise { |result|
max_width = 0
padded_lines = []

lines.each { |line|
max_width = line.length if line.length > max_width
padded_lines.push promise { "%*s" % [ result[1], line ] }
}

[ padded_lines, max_width ]
}[0]
end

-mental

Daniel Nugent

2/24/2006 1:09:00 AM

I don't think I understand what'sgoing on th... oh wait. I see.

both table_name and name are pointing to "CUSTOMERS" and then only
table_name is pointing to "MONKEYS"

Yes, see, the thing that's important to consider is that I'm dumb.

*tries out Mental's examples, figures out how they work*

...

Woah, that's some powerful ju-ju. Maybe I should go and futz with
GhostWriter again anyhow...

On 2/23/06, Jim Weirich <jim@weirichhouse.org> wrote:
> Daniel Nugent wrote:
> > table_name = "CUSTOMERS"
> > x = promise {table_name.dup}
> > table_name = "MONKEYS"
> > puts x
> > =>"CUSTOMERS"
> >
> > Would avoid the problem. Though it's good to point out that you
> > likely want to avoid changing the state of any variable that's
> > captured by a promise closure (unless of course you plan on exploiting
> > just that).
>
> Hmmm ... I just tried it and got "MONKEYS" for the result. It makes
> sense becase by the time table_name is dup'ed in the promise, it has
> already been modified.
>
> This would do it:
>
> def table_promise(name)
> promise { name }
> end
>
> table_name = "CUSTOMERS"
> x = table_promise(table_name)
> table_name = "MONKEYS"
> puts x # => "CUSTOMERS"
>
> --
> -- Jim Weirich
>
>
>
> --
> Posted via http://www.ruby-....
>
>

--
-Dan Nugent

comp.lang.ruby

Re: [ANN] lazy.rb 0.9.5 -- transparent futures!

Daniel Sheppard

Daniel Nugent

Shashank Date

Daniel Nugent

MenTaLguY

MenTaLguY

Daniel Nugent

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