[Sugar-devel] Karma.rand() and Karma.shuffle() remarks

[Tomeu Vizoso]

Adding sugar-devel to CC in case Bert wants to say anything

On Sat, Jan 9, 2010 at 16:36, Peter Gijsels <peter.gijsels at gmail.com> wrote:
> Vaibhaw,
>
> You seem to imply that there is a (difficult) way to extract them,
> could you elaborate?
>
> Do you think it would be useful to have a simple way to extract these
> assets from a .pr file?
>
> I can try to see if I can come up with something. I'm not guaranteeing
> anything, but I think it might be worth a shot. I think it would be
> more fun than cropping screenshots. ;-)
>
> I have two possible approaches in mind:
> 1) There is probably a central place where the .pr is being read in
> and Morph objects are being constructed. If we intercept objects of
> the correct type we can dump their image data to a file. The trick is
> to find the code that does the deserializing which can be rather
> frustrating in Smalltalk if you are not familiar with the code.
>
> 2) The second approach would be to just walk over all objects, see if
> they are an image, and dump them to files.
>
> Do you have a Squeak development image (with development tools like
> the browser and inspector) from which I can read in these .pr files so
> that I can poke around a bit?
>
> Regards,
> Peter
>
> On Sat, Jan 9, 2010 at 3:04 PM, Vaibhaw (Bob) Poddar
> <vaibhawp at yahoo.co.uk> wrote:
>> Afraid not. There is no (easy) way to extract the info from the .pr files. I
>> have been just cropping the images out from the screen shots so far.
>>
>> Vaibhaw (Bob) Poddar
>>
>> Nepal Cell. +977.98510.61345
>> India Cell. +91.99999.15661
>> US of A Cell. +1.415.508.4503
>>
>> http://HimalayanTechies.com
>>
>> On 1/9/2010 7:43 PM, Peter Gijsels wrote:
>>
>> Bryan, Vaibhaw,
>>
>> I've got epaath working on my windows machine.
>>
>> Do I understand correctly that all of the materials of a lesson are
>> contained in one .pr file, e.g. 6_English_actionVerb_3.018.pr? The
>> epaath.image running on the squeak vm loads in that file.
>>
>> Is there an easy way to extract the pictures and sounds from the .pr
>> file of the lesson?
>>
>> Regards,
>> Peter
>>
>> On Thu, Jan 7, 2010 at 5:45 AM, Vaibhaw (Bob) Poddar
>> <vaibhawp at yahoo.co.uk> wrote:
>>
>>
>> Step to get Squeak working on a Windows machine (not sure how on a Linux
>> distribution).
>>
>> Download and install squeak
>> http://www.squeakland.org/download/
>>
>> Replace the etoys.image inside the Etoys/Etyos.app/Contents/Resources with
>> the image file from the E-Paath.
>>
>> That should be it. If you run into any issues I would be happy to look at
>> that.
>>
>> Thanks
>>
>> Vaibhaw (Bob) Poddar
>>
>> Nepal Cell. +977.98510.61345
>> India Cell. +91.99999.15661
>> US of A Cell. +1.415.508.4503
>>
>> http://HimalayanTechies.com
>>
>> On 1/7/2010 7:44 AM, Bryan Berry wrote:
>>
>> here is the file http://karma.sugarlabs.org/Squeak.tar.bz2
>>
>> These are all the Squeak files in the current EPaath. I am not sure how to
>> actually view the individual projects.
>> Vaibhaw: how do we do that? My Squeak skills are rusty
>>
>> On Thu, Jan 7, 2010 at 7:06 AM, Bryan Berry <bryan at olenepal.org> wrote:
>>
>>
>> hey Peter,
>> first could u use pastie.org or jsbin.com for small code samples? makes it
>> easier for everyone to view and comment on your code
>>
>> On Thu, Jan 7, 2010 at 3:47 AM, Peter Gijsels <peter.gijsels at gmail.com>
>> wrote:
>>
>>
>> Hi Bryan,
>>
>> I had a look at the Karma.rand() and Karma.shuffle() functions and
>> have some remarks.
>>
>> Here is a link to some code illustrating the comments below:
>> http://dl.dropbox.com/u/3249723/js-shuffle.tgz
>>
>> It contains the current Karma implementation of these two functions,
>> an alternative implementation (AlternativeKarma) and some code to
>> print some histograms.
>>
>> 1) The values returned by Karma.rand(min, max) are not uniform: the
>> probability of getting min is half of any other element between min
>> and max. The same goes for max. If you use Math.floor i.s.o.
>> Math.round (and adjust the argument to Math.random) you have a uniform
>> distribution.
>>
>>
>> Good point! Let's use your code
>> do you have any idea how we could write a unit test to check that values
>> aren't uniform? That way I don't change it back to a crappy implementation
>> by accident later
>>
>>
>>
>> 2) The Karma.shuffle(array) function does not return each permutation
>> with equal probability. If you work through the math for a three
>> element array you can derive this. Or you can simply make a histogram
>> ;-) In the code linked above I make a histogram and you can see that
>> not every permutation is equally probable. The alternative
>> implementation uses the Fisher-Yates algorithm, and does not have this
>> problem.
>>
>>
>>
>>
>> 3) The unit test for Karma.shuffle is not deterministic: it will fail
>> with a probability 5/5! = 1/24. I do not know of a good way to test
>> these kind of functions. You could do something like the histogram
>> thing in the code above and check that the distribution is roughly
>> uniform. But then the test is still not deterministic and if you want
>> a small chance of failure, running the test would take a bit of time.
>> Maybe one thing that you should check is that the result of calling
>> shuffle() contains the same elements as the original (sort both and
>> see that they have the same elements in the same position).
>>
>>
>> Ouch, you can tell that my CS fundamentals are pretty weak ;)
>> I think that shuffling only 5 elements isn't really a valid test, better
>> to shuffle 25 elements and see if it fails out of 100 tests. I think 1/500
>> is a tolerable failure rate, what do u think?
>> let me test that out now
>>
>>
>> On an unrelated note, did you have time to prepare a download link
>> with the Squeak stuff? Tomorrow evening I have some time to have a
>> look at it.
>>
>> Regards,
>> Peter
>>
>>
>> Sorry I uploaded most of the files but forget to upload one important
>> file, the squeak image ;). I will upload that now and send you the link
>> shortly
>>
>>
>>
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>



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