Beginners February 2008

beginners@lists.squeakfoundation.org

56 participants
54 discussions

Re: [BUG] Inconsistent float soustraction
by cdrick 18 Feb '08

18 Feb '08

> > Hi, > > > > I noticed in my image (damien last beta so 3.10 - windows XP and > > Vista) that I have a strange bug when soustracting floats > > successively. Here is how I reproduce it in a workspace: > > > > 1 - 0.2 -0.05 -0.3 = 0.45 "true" > > 1 - 0.2 -0.05 -0.3 -0.1= 0.35 "true" > > 1 - 0.2 -0.05 -0.3 -0.1 - 0.10= 0.25 "*****false*****" > > 1 - 0.2 -0.05 -0.3 -0.1 - 0.10= 0.24999999999999995 true > > > > or again: > > 1 - 0.1 = 0.9 true > > 1 - 0.1 - 0.1 = 0.8 true > > 1 - 0.1 - 0.1 - 0.1 = 0.7 false > > > > > > Can somebody explain that or is it a bug ? I don't know yet if it's > > specific to my image, so does other have the same behavior? > > I can force the rounding of the result but find it strange. > > > > Cédrick 2008/2/17, danil osipchuk <danil.osipchuk(a)gmail.com>: > This is not even squeak specific. Decimal floats not always can be > represented precisely in binary form: > > http://en.wikipedia.org/wiki/Floating_point#Accuracy_problems > > Hi Cédrick, > > if you need to operate with exact precision just don't trust floats. Use ScaledDecimals instead. In Squeak ScaledDecimals are implemented with the fraction so it's matematically stronger than floats. Use floats at presentation or user interface time and evade them at domain model. > > cheers, > > Sebastian Sastre uhm ok, good to know. Actually, it was just a test that failed so I was surprised. I still find the result odd. Seeing ScaledDecimal>>testConvertFromFloat, I'm wandering if it would be better to have Float>>= considering egality if the difference is less than 1.0e-9. <primitive: 47> aNumber isNumber ifFalse: [^ false]. ^ (aNumber asFloat - self) abs < 1.0e-9 I would prefer having = working as I expect, even if it would be wrong for smaller values than 1.0e-9. For strict egality, == can be used. Is it possible to disable a primitive call like here (it's optimized no ?) ? Anyway, thanks for your answers. Cédrick

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Floating point arithmetic
by Richard Karpinski 17 Feb '08

17 Feb '08

Would rounding help? The problem is pretty well explained in that mailing, but surely, when we are doing arithmetic to two or three decimal places, there will be some way to ask that the result be rounded to that many places. As long as the numbers remain close to 1, it may be easier to deal with that than forcing the calculations into rational arithmetic. I have observed rooms full of professors and hardware designers arguing over these details for months on end, eventually producing fifty to one hundred page documents to say how it should work. See IEEE-754 for a serious definition of a good computer arithmetic. It is indeed very hard to cover all the cases and make it useful as well. Dick On 2008, Feb 17, in beginners-request(a)lists.squeakfoundation.org: >>> 1 - 0.2 -0.05 -0.3 -0.1= 0.35 "true" >>> 1 - 0.2 -0.05 -0.3 -0.1 - 0.10= 0.25 "*****false*****" >>> 1 - 0.2 -0.05 -0.3 -0.1 - 0.10= 0.24999999999999995 true ... >>> Can somebody explain that or is it a bug ? I don't know yet if it's >>> specific to my image, so does other have the same behavior? >>> I can force the rounding of the result but find it strange.

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Morphic Questions
by Jeffrey Straszheim 16 Feb '08

16 Feb '08

I have some basic intro questions on Morphic. I'm digging through the source code, and reading what I can find on the web, but it is quite a lot to take in. 1. Messages There seem to be at least 2 ways to handle messages with Morphic. The subclassing way, overriding methods such as *handlesMouseDown* and so on, and *on:send:to:* way. What are the differences between the two, and why would I prefer one over the other? 2. MorphicModel The MorphicModel class appears to be for morphs that implement the view side of MVC. However, I find the source rather confusing. What on earth is a *slotSelector*, for instance? And a method like *compileAccessForSlot* just leaves me baffled. What is this class for, and are there any simple examples of its use? 3. PasteUpMorph I know that the screen background is a PasteUpMorph, but I see them mentioned elsewhere from time to time. What exactly is a PasteUpMorph? Would I ever want to use one? Is there a simple example? Thanks in advance for your help. P.S. I just figure out how to make balloon text work. This stuff is cool! -- Jeffrey Straszheim http://straszheim.50megs.com

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unique items in a collection
by Frank Urbach 15 Feb '08

15 Feb '08

Dear list, sometimes I get a collection with many items in it and want to get a collection where the occurrencesOf: each item should 1. So I'm searching for an selector like 'unique'. Is there a such a thing? Cheers, Frank Edelstahlwerke Schmees GmbH Geschäftsleitung Clemens Schmees Sitz D-01796 Pirna Handelsregister Dresden HRB 54 E-Mail: es.la(a)schmees.com WEB: www.schmees.com Diese E-Mail enthält vertrauliche und/oder rechtlich geschützte Informationen. Wenn Sie nicht der richtige Adressat sind oder diese E-Mail irrtümlich erhalten haben, informieren Sie bitte sofort den Absender und vernichten Sie diese Mail. Das unerlaubte Kopieren sowie die unbefugte Weitergabe dieser Mail ist nicht gestattet. This e-mail may contain confidental and/or privileged information. If you are not intended recipient or have received this e-mail in error, please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of the material in this e-mail is stictly forbidden.

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Important reminder - Squeak Foundation Election 2008!
by goran＠krampe.se 15 Feb '08

15 Feb '08

Dear Squeakers, This is primarily a reminder for *nominating board member candidates*! The deadline for nominations is 22nd February and that is VERY SOON! For the full schedule, see below. Our current nominees are: Bert Freudenberg (serving on the board currently) Yoshiki Ohshima (serving on the board currently) Both Bert and Yoshiki were nominated by Kim Rose, VPRI. Every year we elect the Squeakfoundation Board (http://www.squeak.org/Foundation) consisting of seven members from our community. The exact duties of this board is not fully defined and there are definitely varying ideas on how it should work and what we expect from it - this is also why it is so important for us all to nominate candidates and to lket the candidates present their views and ideas! For more information about the board, see Ron's recent email: http://lists.squeakfoundation.org/pipermail/elections/2008-February/000 223.html Let me remind us all of the schedule: Now through 22nd February (circa 8 days!!!!!): Nominations of board members Candidates should nominate themselves on the squeak-dev mailing list. Or if you nominate someone else, make sure that person really wants to run. :) 22nd February to 29th February: Campaigning period During this period the candidates should ideally present themselves and the community can ask questions. We will probably organise some form of structured Q&A activity - details to follow soon. 1st march 6PM (18.00) UTC: Online election starts using the CIVS system The voting period is one week long and ballots are sent out via email. Only Squeakers rated as Apprentice (or higher) on people.squeakfoundation.org are eligible to vote - make sure your email address is up to date there!!! 8th march 6PM (18.00) UTC: Online election ends Results will be announced as soon as possible on the 8th or 9th. IMPORTANT: In order to vote - be sure to confirm that you have an account on people.squeakfoundation.org and that your email address is up to date. If you are not already registered on the site do so as soon as possible. Include information about your participation in the Squeak community to aid everyone in determining your appropriate certification. If you have an account but cannot access it any longer please email box-admins(a)lists.squeakfoundation.org and specify your account name. When the voting period starts all voters will receive an email with instructions and a link to the voting website. If there are any further questions, just reply and I will follow up on squeak-dev. More information and details will follow and everything about the election can be tracked here: http://wiki.squeak.org/squeak/6025 regards, Göran Krampe on behalf of the Election Team

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Screensaver detection
by Uwe Loew 13 Feb '08

13 Feb '08

Hello squeak professionals, in our process monitoring software we use a background process to update the displayed values. breakFlag := false. delay := Delay forMilliseconds: 10. Processor fork: [ [ breakFlag ] whileFalse: [ backgroundProcess := true. "Process is now active " delay wait. ........................................."calling the GUI update methods displaying the measured values from the process" delay wait. ]. backgroundProcess := false. "Process is going to terminate " ] at: Processor userPriority - 5 Processor is an instance of ProcessScheduler. Something in our GUI update software wastes memory and over some days crashes the system. So the user has to stop the background display process when leaving the system and to restart it when coming back. We now want to automate this switching on and off of the GUI updates by checking the screensaver status of windows. Our wish is to check in each update cycle, whether the windows-screensaver is on, and depending on this status, to update the GUI display or not. Can anybody of you give us a hint, how to check, whether windows has switched of the desktop-display and displaying the screensaver, or is still displaying the desktop containing the squeak window? Thank you very much. Best regards Uwe

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Simple Precedence question
by Jeffrey Straszheim 13 Feb '08

13 Feb '08

So, I'm learning Smalltalk for the first time, and I have a very simple question regarding the precedence of the cascade operator. So, in this expression: self something: anObject selector ; anotherSelector. Is the target of *anotherSelector* anObject, or self? In other words, does it parse like this self something: (anObject selector ; anotherSelector). or self something: (anObject selector) ; anotherSelector. Also, what is the general principle that determines this. Thanks in advance. -- Jeffrey Straszheim http://straszheim.50megs.com

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RE: kindlelab
by Ted Jordan 13 Feb '08

13 Feb '08

now that is a good one to know about!! :-) ted Message: 3 Date: Tue, 12 Feb 2008 13:35:47 -0600 From: "Rich White" <rich.lynn.white(a)gmail.com> Subject: Re: [Newbies] does squeak offer ways to control wirelessly? To: "A friendly place to get answers to even the most basic questions about Squeak." <beginners(a)lists.squeakfoundation.org> Message-ID: <b99b40cb0802121135m445789d1ma5181c42cb2a074e(a)mail.gmail.com> Content-Type: text/plain; charset="utf-8" There is also a growing Kindlelab users group here - http://kindlelab.com & http://kindlelab.ning.com doing just that. Cheers, Rich ===== On Feb 12, 2008 1:27 PM, Eric Eisaman <eric.eisaman(a)gmail.com> wrote: > Hello Ted, > > You should be able to run Johnny Lee's program to keymap a Wiimote to key > events which trigger control responses in your Squeak programs. > > Regards, > Eric Eisaman > > On Feb 9, 2008 4:00 AM, Ted Jordan <ted(a)funutation.com> wrote: > > > if not, would that be something that could be created simply? > > > > thanx > > ted > > > > -- > > > > ted jordan, principal ted(a)funutation.com > > Funutation Tekademy LLC > > Making the World Computer Smarter > > > > http://funutation.com US Bank Building > > 216 378 9035 p 24700 Chagrin Blvd, Ste 201A > > 216 926 3905 p Beachwood, OH 44122 > > USA -- ted jordan, principal ted(a)funutation.com Funutation Tekademy LLC Making the World Computer Smarter http://funutation.com US Bank Building 216 378 9035 p 24700 Chagrin Blvd, Ste 201A 216 926 3905 p Beachwood, OH 44122 USA

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does squeak offer ways to control wirelessly?
by Ted Jordan 12 Feb '08

12 Feb '08

if not, would that be something that could be created simply? thanx ted -- ted jordan, principal ted(a)funutation.com Funutation Tekademy LLC Making the World Computer Smarter http://funutation.com US Bank Building 216 378 9035 p 24700 Chagrin Blvd, Ste 201A 216 926 3905 p Beachwood, OH 44122 USA

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e-completion question
by itsme213 11 Feb '08

11 Feb '08

I'm using the latest version of e-completion and cannot get some options to work, using either Ramon's image or Damien's dev image. c-h - help c-u - typed or untyped mode c-t - include or exclude Object All three just make the e-completion menu disappear. Any suggestions? Thanks - Sophie

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Beginners February 2008