On 09.09.2014, at 04:49, David T. Lewis <lewis at mail.msen.com> wrote:

> On Mon, Sep 08, 2014 at 01:09:17PM -0700, Eliot Miranda wrote:
>> On Mon, Sep 8, 2014 at 11:58 AM, Bert Freudenberg <bert at freudenbergs.de>
>> wrote:
>> 
>>> On 08.09.2014, at 20:45, Eliot Miranda <eliot.miranda at gmail.com> wrote:
>>> 
>>> Instead of creating an exception handler why not modify the interpreter to
>>> answer nil?  I know the answer is that the Interpreter doesn't, and fails.
>>> But we've had years in which we could change the Interpreter to match
>>> vmParameterAt: and instead of doing the good thing (have the Interpreter
>>> answer nil for values answered by Cog VMs), we force the standard system to
>>> waste time.  We should optimize the common case (trunk running on Cog) not
>>> penalize it to cover the uncommon case (trunk running on Interpreter VM).
>>> 
> 
> All of the VMs, including Cog, behave identically in this regard. If you
> request a VM parameter that is not understood by the VM, the primitive fails.
> 
>>> 
>>> Nah, if performance really was an issue we could just remove the
>>> primitiveFailed in vmParameterAt:. No need to change the VM.
>>> 
>> 
>> That's a good idea.  Change the primitiveFailed to ^nil.
>> 
> 
> It would be a good idea if performance was actually an issue. It is not.
> 
> This is a case where using exceptions makes good sense. If some arbitrary
> VM cannot satisfy a primitive request, it should fail the primitive.
> Answering nil as a flag for primitive failed is bad karma, and should
> not be done unless there is a good reason for doing so. Improving the
> performance of #isRunningCog is not a good reason.
> 
> BTW there is another method with the same problem:
> 
>  isRunningCogit
>    "Answers if we're running on the Cog JIT"
> 
> There are no senders of #isRunningCogit in the image, so it does not need
> to be fixed.  But the #isRunningCog bug was breaking the unit tests, so
> it needed fixing.
> 
> Dave

+1

- Bert -



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