[Newbies] Modify block (closure) parameters

[Casey Ransberger]

These should be informative:

http://www.mirandabanda.org/cogblog/2008/06/07/closures-part-i/
http://www.mirandabanda.org/cogblog/2008/07/22/closures-part-ii-the-bytecodes/
http://www.mirandabanda.org/cogblog/2008/07/24/closures-part-iii-the-compiler/


On Tue, Aug 6, 2013 at 2:14 PM, Louis LaBrunda <Lou at keystone-software.com>wrote:

> Hi Guys,
>
> FWIW, VA Smalltalk doesn't allow changing block arguments.
>
> Lou
>
> On Tue, 6 Aug 2013 13:42:33 -0700, Casey Ransberger
> <casey.obrien.r at gmail.com> wrote:
>
> >I didn't read your post clearly enough. Yep, that would seem odd. You may
> >have a bug there. I'm not sure why that happens. It looks like the outer
> >context isn't taking the assignment, but hanging onto the initial value it
> >receives from #value:.
> >
> >I'm not totally sure we should expect to be able to do what you're trying
> >to do in modern Squeak. I haven't assigned to a block arg in a long time
> (I
> >keep allow block assignments off unless I'm loading old code.) I don't
> know
> >what the status is there. I run a relatively recent Cog VM on a 10.7.5 Mac
> >and I'm seeing the same behavior in Squeak 4.4.
> >
> >When I switch to an old VM (3.8.18Beta3U) and run Squeak 3.0, your snippet
> >works as expected. I'm not sure if this is in the image or the VM yet, or
> >whether it's expected behavior or not with allowBlockArgumentAssignment
> >(Again, I usually turn it off.)
> >
> >The main take away here is, don't do that:) as it's a back-compat feature
> >and it really ought to have a big sign on it that says DEPRECATED. If
> >you're trying to load some older code and running into this, it might be
> >better to actually rewrite it not to assign to block arguments in my
> >opinion (and maybe I'm nuts.)
> >
> >Can you tell me what VM you're using?
> >
> >Smalltalk vmVersion "this will tell us"
> >
> >And also which version of Squeak?
> >
> >SmalltalkImage current systemInformationString "ditto"
> >
> >Also, what's the OS of the host system?
> >
> >
> >
> >On Mon, Aug 5, 2013 at 1:44 AM, psea <denis.lukichev at gmail.com> wrote:
> >
> >> Hi Smalltalkers!
> >>
> >> Here is a question I can't find answer with google.
> >> In short: Does block parameters and block local variables are the same
> >> thing
> >> (semantically) inside closure? It looks like it's not. Below the
> >> explanation.
> >>
> >> ===================
> >> Here is the accumulator function (first attempt):
> >>
> >> makeAcc := [ :acc |
> >>         [:n | acc:=acc+n. acc]]
> >>
> >> It turns out it doesn't work as intended:
> >>
> >> a1 := makeAcc value: 10
> >> a1 value: 1 => 11
> >> a1 value: 1 => 11
> >> a1 value: 2 => 12
> >>
> >> ====================
> >> Here is the second attempt:
> >>
> >> makeAcc := [ :acc |
> >>         | total |
> >>         total:=acc.
> >>         [:n | total:=total+n. total]]
> >>
> >> And it does work as intended:
> >>
> >> a1 := makeAcc value: 10
> >> a1 value: 1 => 11
> >> a1 value: 1 => 12
> >> a1 value: 2 => 14
> >>
> >> So if we use the local variable to store accumulator it works as it
> should
> >> and remembers the value between function (block) calls. But if we use
> block
> >> parameter to store the value of accumulator it does not remembers the
> value
> >> between calls.
> >> Why is it so?
> >>
> >> P.S. Sorry for my English. I do all my best.
> >>
> >>
> >>
> >> --
> >> View this message in context:
> >> http://forum.world.st/Modify-block-closure-parameters-tp4702118.html
> >> Sent from the Squeak - Beginners mailing list archive at Nabble.com.
> >> _______________________________________________
> >> Beginners mailing list
> >> Beginners at lists.squeakfoundation.org
> >> http://lists.squeakfoundation.org/mailman/listinfo/beginners
> >>
> -----------------------------------------------------------
> Louis LaBrunda
> Keystone Software Corp.
> SkypeMe callto://PhotonDemon
> mailto:Lou at Keystone-Software.com http://www.Keystone-Software.com
>
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>



-- 
Casey Ransberger
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