What would Squeak be like without non-local returns
reefedjib at yahoo.com
Thu Nov 8 06:22:59 UTC 2007
----- Original Message -----
From: "Ralph Johnson" <johnson at cs.uiuc.edu>
To: "The general-purpose Squeak developers list"
<squeak-dev at lists.squeakfoundation.org>
Sent: Wednesday, November 07, 2007 9:55 PM
Subject: Re: What would Squeak be like without non-local returns
> On 11/7/07, Andreas Raab <andreas.raab at gmx.de> wrote:
>> Ralph Johnson wrote:
>> > Consider the code
>> > object eventual: [... ^3]
>> > ...
>> > ^4
>> > Depending on the missing code, it could return either 3 or 4. If not,
>> > something is very strange, and the language is no longer Smalltalk.
>> Not at all. Eventual/future sends introduce a new unit of concurrency
>> and the only thing we're arguing is whether that second unit of
>> concurrency will be executed before the first one. In E/Croquet this is
>> not possible, but it is really no different from, e.g.,
>> [^3] forkAt: Processor activePriority-1.
>> When you run this, it will return 4 (every time) and fall over the
>> non-local return later (every time).
> But that wasn't what I said. Your code is different from mine. Note the
> For example,
> Object >>foo
> [^3] fork.
> self halt.
> ^ 4
> returns 3.
No, this halts, on the calling Process, and signals a BlockCannotReturn
Error, on the forked Process, presumably because the returnContext is nil.
Without the halt and with any number of statements (...), it would return 3.
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