[Vm-dev] Help/advice tracking down a squeak-vm regression

[David T. Lewis]

On Tue, May 08, 2012 at 10:44:26AM +0100, Alex Bradbury wrote:
>  
> David and Igor: thanks for your responses. Comments below.
> 
> On 7 May 2012 00:28, David T. Lewis <lewis at mail.msen.com> wrote:
> > If I remember correctly, Scratch derives from a Squeak 3.6 image and uses
> > a VM of similar vintage. Since the days of Squeak 3.6, there have been
> > a number of fundamental changes in the Squeak VM. I recall some discussion
> > of this perhaps a couple of years ago, and I think that the prevailing
> > view was that it made more sense to bring the Scratch image up to date
> > with respect to the VM changes, as opposed to trying to make a single
> > VM that could be backward compatible all the way to Squeak 3.6.
> 
> Though the current squeak image did work flawlessly in squeak-vm 4.0?
> So the upstream view is that this is not officially supported and the
> correct solution if it no longer works on 4.4 is to just use an older
> vm?
> 
> > From a license point of view, is there any reason that the Scratch VM
> > and source code could not be distributed on Debian? If this is acceptable,
> > then I expect that the fastest way to achieve a working distribution would
> > involve arranging for Scratch to run using a VM at e.g. /usr/bin/scratch,
> > and Squeak to run with /usr/bin/squeak or /usr/bin/cog.
> 
> It does seem that the Ubuntu packages bundles its own
> scratch_squeak_vm. Either that, or supporting the installation of
> squeak-vm 4.0 alongside 4.4 might be good options. For my purposes
> with the Raspberry Pi, I'm probably just going to install and pin the
> squeeze squeak-vm (4.0) until a better solution comes along.
> 
> Alex
 
On 8 May 2012 10:44, Alex Bradbury <asb at asbradbury.org> wrote:
> > Though the current squeak image did work flawlessly in squeak-vm 4.0?
> > So the upstream view is that this is not officially supported and the
> > correct solution if it no longer works on 4.4 is to just use an older
> > vm?
>  
> squeak image -> scratch image
>  
> Alex

As far as I know, Scratch images have not worked on standard Squeak VMs
for a number of years, and Scratch has always relied on shipping its
own VM. In addition to fundamental changes in the VM itself that have
taken place in recent years, I believe that the Scratch version of the
VM also includes a couple of plugins (add-in functionality) that are
required for Scratch but not included in Squeak.

I think I see one source of confusion here. I just read the link at
http://info.scratch.mit.edu/Source_Code and find the following statement:

 "Since Scratch simply uses a stock Squeak virtual machine, we are
  not distributing the Squeak virtual machine source code. Both the
  source code and pre-compiled binaries for the Squeak virtual machine
  are available at www.squeakvm.org."

Unfortunately, I don't think that this is true, and hopefully someone
can make a correction to that web page.

The squeakvm.org code repository along with VMMaker at source.squeak.org
does contain fully versioned copies of the Squeak VM, presumably including
all or most of the code in the current Scratch VM (except for the Scratch
specific plugins). So it would probably be possible to build a working
Scratch VM using code from the standard Squeak VM repositories. But
I fear this would take some work on the part of someone who knows
Scratch well enough to find and build the right versions and put the
pieces together.

Dave