If you want to return from the block directly (but not from the containing method), here are some options:


[:x | x ifNil: [#plonk] ifNotNil: [x + 1]].

[:x | x ifNil: [thisContext return: #plonk] ifNotNil: [x + 1]]. "metaprogramming, usually disregarded!"


Best,

Christoph

________________________________
Von: Squeak-dev <squeak-dev-bounces at lists.squeakfoundation.org> im Auftrag von Lauren P <drurowin at gmail.com>
Gesendet: Montag, 28. November 2022 18:01:42
An: The general-purpose Squeak developers list
Betreff: Re: [squeak-dev] Full block closure return value testing/using in workspace?

I read somewhere to never write ^ in a block you intend to give out.  I use it to abandon methods in assertions and never any other time.

One thing I do know from experimentation is it marks the method finished, so you can't call the block twice.  You'll get BlockCannotReturn nowadays.  It used to be a segmentation fault.

On Mon, Nov 28, 2022, 04:33 LawsonEnglish <LEnglish5 at cox.net<mailto:LEnglish5 at cox.net>> wrote:
OK, thanks.

I had thought perhaps it would act more like a break and take one to the outside of the block, but instead it returns to the caller, as I should have realized.

Stilly me.

L


> On Nov 28, 2022, at 04:15, Tobias Pape <Das.Linux at gmx.de<mailto:Das.Linux at gmx.de>> wrote:
>
> Hi Lawson
>
> good to see you.
>
>> On 28. Nov 2022, at 11:58, LawsonEnglish <LEnglish5 at cox.net<mailto:LEnglish5 at cox.net>> wrote:
>>
>> I was trying to test some ideas and was using the new FullBlockClosure to return values for further use in a workspace.
>>
>> This works with “print it”:
>>
>> [Transcript show: 2;cr. ^2] value => 2
>>
>> This does not work:
>>
>> test := [Transcript show: 2;cr. ^2] value <do it>
>>
>> test => nil.
>
> Yes, and that is expected.
>
> Two things:
> First, it seems you want to assign the _return value_ of a block to a variable.
> To achieve this, do
>       test := [Transcript show: 2;cr. 2] value "Note the missing caret/return"
>
> This is because the last statement of a block will be its return value.
>
> Second, yes, the return/caret in the block does something but apparently not the thing you expected.
> The effect for caret/^/return is:
>
>       ^ statement "Returns the value from statement from the method"
>
> The last word is crucial. You return from the method, regardless of the block you are in.
>
> Like so:
>
> fooo
>
>  Transcript showln: 'foo 1'.
>  self bar:
>    [Transcript showln: 'block 1'.
>    ^ 1].
>  Transcript showln: 'foo 2'.
>  ^ 2.
>
>
> bar: aBlock
>
>  Transcript showln: 'bar 1'.
>  aBlock value.
>  Transcript showln: 'bar 2'.
>
>
> If you send #foo, transcript will contain
>
> foo 1
> bar 1
> block 1
>
> an the return value will be 1.
>
> This is because the Return in the block will return form the _method #foo_  (where the block is defined) and not only from the block.
>
> What does that have to do with the Workspace???
>
> Workspaces create artificial methods for doIts and PrintIts.
>
> Hence, your actually sent method looks like that:
>
> DoIt
>  test := [Transcript show: 2;cr. ^2] value
>
> If you run that method as print-it, "^2" returns form the DoIt method and the workspace can print the 2.
> If you run that method as print-it, "^2" returns form the DoIt method but the assignment has never taken place, so test remains at its previous value, wich is nil.
>
> I hope this helps.
>
> Best regards
>       -Tobias
>
>>
>> nor does this:
>>
>> test :=( [Transcript show: 2;cr. ^2] value) <do it>
>>
>> test => nil
>>
>> print it still works:
>>
>> test := ([Transcript show: 2;cr. ^2] value) => 2
>>
>> test => nil.
>>
>> In all cases, a 2 appears in the Transcript window, so I know that *something* is happening.
>>
>> I would have thought that if print-it and  do-it work, then the returned value would be put in the test variable, but that is not the case.
>>
>> I can use a  workspace global variable to access the output, but that kinda makes the ^ a one-trick-pony: useful for breaking out of loops, but not giving me access to the return value.
>>
>>
>> [test := 2. Transcript show: test;cr. ^test] value => 2
>>
>> test => 2
>>
>> Is this an oversight or bug or feature for workspaces, or is it working as intended?
>>
>>
>> Lawson
>>
>>
>>
>
>
>


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