Squeak-dev April 1998

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107 participants
279 discussions

Re: bit shifting
by glenn 28 Apr '98

28 Apr '98

I think it's even a bit stronger than "to allow implementations to provide features...". On a number of occasions, we made things "undefined" to *encourage* implementations so that, we hoped, this would lead us (and our descendants) to extend the Standard by codifying then-existing practice. So not only would it not be counter to the Standard for Squeak to take a position on negative bit operations (apologies for the tripple negative), but it might be in the best interest of long-term Smalltalk standardization for Squeak to do so. glenn At 08:49 AM 4/23/98 -0700, Allen Wirfs-Brock wrote: >At 10:23 PM 4/22/98 -0700, Dan Ingalls wrote: >... >>I'm still mildly opposed to bit manipulation on negative numbers, mainly for >>simplicity, although ANSI compliance is a weak second reason. > >ANSI Smaltalk doesn't forbid bit manipulations on negative numbers, it says >that the result of such an operation is undefined. > >In this context "undefined" means: "If a feature is denoted undefined a >conforming implementation may accept a program using the feature, but must >document that it does so. A conforming implementation is not required to >accept an undefined feature. A program that is dependent upon the use of an >undefined feature does not conform to the standard." (section 2 page 7) > >"undefined" is a very important concept within the standard. It is one of >the main hooks used to allow implementations to provide features that go >beyond what is in the standard. > >Allen_Wirfs-Brock(a)instantiations.com > > >

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Re: [Q] Ask on String manipulation
by glenn 28 Apr '98

28 Apr '98

At 12:41 PM 4/28/98 +0900, Chun, Sung Jin wrote: >I want to make string like in ObjC; >[ str concatSTR: 'Hello' ]; >But in Smalltalk I cannot find it. >And also I want printf like feature in error: like this; >self error: 'Class %s', [ self name ] >Can anyone teach me how I can do this ? We extended VisualWorks some time back to handle this kind of string "macro expansion", including arguments, by adding an #expandMacrosWith:* family of messages and creating a class (StringParameterSubstitution) to do the work. For example: 'hello, <1s>' expandMacrosWith: 'Chun' returns 'hello, Chun' or '<1?Guten Tag:Hello>, <2s>' expandMacrosWith: isGerman with: 'Chun' returns 'Guten Tag, Chun' or 'Hello, Chun', depending on the value of the boolean isGerman. As you suggest, this is used a lot in error handlers and other places, especially in the face of internationalization. I don't think it's a huge project to create this functionality in Squeak, and while you can't steal the VW code, I think we'd benefit from having compatible syntax, so I'd encourage you or some other Squeaker to check out the VW description. glenn

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RE: HELP! formalizing OO
by Lex Spoon 28 Apr '98

28 Apr '98

Though it's infeasible to prove a program correct, how about proving things like "consistent" or "safe"? Even if it's too hard to prove that a robot arm will build a car, it would seem reasonable to prove things like, the arm doesn't start drilling holes in itself or in nearby workers. To an extent this is already done via type-checking of various sorts. But type-safety is a pretty weak constraint. Such things wouldn't give you a proof of correctness in a traditional sense, but they would you help convince *yourself* that a program is likely to work properly. Lex Jarvis, Robert P. writes: > I think this is an interesting topic. Being able to come up with a > proof of a given programs correctness would be wonderful, but I think > this is often impractical in the "real world". To be able to prove that > a program will behave correctly you have to define what the correct > behaviors are, and in many cases the definition of "correct behavior" is > a moving target. So you may be able to prove that a program meets a set > of specifications which existed at some time, but can you then prove > that the specifications are correct? The chicken and the egg trade > places, the wyrm devours its tail, and we > iterate again. :-) There's also an analogy here to solving some > production optimization problems which are at once too complex and too > loosely defined for solution by traditional methods. What you find is > that although you may not be able to determine the "optimal" solution, a > "near-optimal" solution is good enough and requires a fraction of the > computation time. In software I think that providing an environment > where correctness is probable, if not provable, is probably the "near > enough" solution. > > Bob Jarvis > The Timken Company > > >-----Original Message----- > >From: Steve Dekorte [SMTP:steve@inquisit.com] > >Sent: Monday, April 27, 1998 8:39 PM > >To: squeak(a)cs.uiuc.edu; dnelson(a)redwoodsoft.com; David-Joerg(a)deshaw.com > >Cc: The recipient's address is unknown. > >Subject: Re: HELP! formalizing OO > > > > > >Florin wrote: > >>..I would say though that math looks to me like it > >>is still ticking, > > > >An interesting thing about math/logic is that it can prove some of > >it's own limitations. > > > >I think I remember hearing about proofs of the insolvability of the n>2 body > >problem > >and of general solutions to finding the roots of polynomials above a certain > >order. > > > >If these problems are provably insolvablable, should we have much > >confidence in what seem to be the more complex problems of large programs > >being solvable? (By solvable I mean knowing everything about what they > >do without actually running them) > > > >I think most everyone sees that complex programs (like n>2-body problems) > >can't be analyzed without computation, so there are two choices. > > > >The top-down approach is to attempt to make programming langagues more > >analyzable before computation (Strong typing, etc) so correctness can be > >proven. > >This approach is basically out to eliminate the dynamic aspects of the system > >that lead to complexity. (Of course if Smalltalk can be written in ADA, how > >is ADA more provably correct or "safe"?) > > > >The bottom-up approach is to look for new ways of managing complexity so > >correctness > >is more probable. OO of the Smalltalk type is, IMO, an example of the 2nd > >approach. > >It looks at real the source of chaos - excessively coupled equations (via > >variables) > >and structures the langauge to make this problem easier to avoid. > > > >So while the top-down thinkers are unsuccessfully trying to make correctness > >provable, > >the bottom-up thinkers are successfully making correctness more probable. > > > >Steve > > >

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Sending the same message to three StringMorphs
by Philippe de Rochambeau 28 Apr '98

28 Apr '98

Let us say that you would like a ButtonMorph to send a particular command to three different StringMorphs. This command should tell each StringMorph to replace its contents by a particular value (its name, location, size, the value of an instance variable, etc.) How would go about implementing this since Morphs can only have one target? Another question, how would you go about telling a TextMorph to aks an adjacent StringMorph to display its contents (the TextMorph's) whenever the user pressed a ButtonMorph. I have tried creating an instance variable called StringMorph in the TextMorph, but to no avail. Any help on this matter would be much appreciated. Philippe de Rochambeau

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Re: An Education Argument for Squeak
by CYNTHIA NELSON 28 Apr '98

28 Apr '98

Hi Everyone, I think this is significant. I took CS2390 in the Winter Quarter 1998. I was one of the few people who used MVC in the first project which was a design documentation project but no code to be written. However, I missed part of the questions on MVC on the midterm. I think I did not really have a adequate understanding of how MVC works in Squeak even though I had used it on a few small programs in Java and C++. I am not even sure I understood MVC that well. My guess is the students this quarter probably had a much better understanding of MVC by the time they took the midterm. Cindy Nelson At 04:27 PM 4/27/98 -0400, you wrote: > >Last week was the midterm exam, and again, I included a very similar >problem to ones I've used before. Here are the results for the last four >offerings of this course (grades normalized to between 0 and 1.0). > > Averages Sttdev >CS2390Sp98 0.864705882 0.26834552 >CS2390W98 0.539622642 0.34186272 >CS2390Sum97 0.536170213 0.39902234 >CS2390Sp97 0.441568627 0.36106493 > >Is the Spring 98 Quarter (now) *REALLY* better than Winter 98? I had the >same grader and the same grading scale last quarter and this. I did a >one-tailed T-test on the two sets of grades datas. p=4.4E-13 is much less >than 0.05, so I think I'm safe claiming statistically significant >difference. > >I plan to write a technical report on this soon, but I thought that y'all >might be interested in some raw, early results. > >Mark > >-------------------------- >Mark Guzdial : Georgia Tech : College of Computing : Atlanta, GA 30332-0280 >(404) 894-5618 : Fax (404) 894-0673 : guzdial(a)cc.gatech.edu >http://www.cc.gatech.edu/gvu/people/Faculty/Mark.Guzdial.html > > > > **************************************************************************** ******************************* Cynthia L. Nelson Phone: (770) 382-8627 202 Jimmie Nelson Rd SW Fax (770) 382-8630 Kington, GA 30145 e-mail: cindynelson(a)abraxis.com

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Re: Simple Morphs
by Philippe de Rochambeau 28 Apr '98

28 Apr '98

> a target object > a selector to be sent > an optional list of arguments for the message > when to do the action (on mouse down, > repeatedly while down, or on mouse up) What is a selector? >You can actually set all of these using menu commands. To >set the target, put the button over the desired target morph >and then use the "set target" menu command on the button. I can't find any "set target" menu command in the popup menu. How do you tell a button to change a TextMorph's contents to "Hello World"? Many thanks. Philippe de Rochambeau

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Re: Newbie's question: how do you create a chessboard in Squ
by Sam Adams 28 Apr '98

28 Apr '98

Try this goodie from the KSC archive. Once installed, use it to generate a array of relative Rectangles (origins and corners are points with coordinate values between 0.0 and 1.0) Add it to the Rectangle class. This was originally written by Ken Auer (kwa) while at KSC. subDivideBy: aPoint "kwa -- 19 September 1989, Answer a collection of rectangles which divide the receiver evenly into aPoint x columns and aPoint y rows. Answer the new rectangles left to right then down. Yes, this method could be much shorter, but I tried to minimize duplications of arithmetic for efficiency." "KSC Extension" "(0@0 corner: 100@100) subDivideBy: 4@2" "(0.0(a)0.0 corner: 1.0(a)1.0) subDivideBy: 3@1" "<----- use something like this to generate relative rectangles for subview layouts" "commented out asInteger below to support rectangles defined by floats - ssa 11/13/97 14:36" | rows columns eachWidth eachHeight subRegions rowTop baseIndex myLeft rowBottom columnLeft columnRight | columns _ aPoint x. rows _ aPoint y. eachWidth _ (self width asFloat / columns asFloat) "asInteger". eachHeight _ (self height asFloat / rows asFloat) "asInteger". subRegions _ Array new: columns * rows. rowTop _ self top. baseIndex _ 0. myLeft _ self left. 1 to: rows do: [:rowNumber | rowBottom _ rowTop + eachHeight. columnLeft _ myLeft. columnRight _ columnLeft + eachWidth. 1 to: columns do: [:columnNumber | subRegions at: baseIndex + columnNumber put: (self species origin: columnLeft @ rowTop corner: columnRight @ rowBottom). columnLeft _ columnRight. columnRight _ columnRight + eachWidth]. rowTop _ rowBottom. rowBottom _ rowBottom + eachHeight. baseIndex _ baseIndex + columns]. ^subRegions Sam S. Adams, Distinguished Engineer, IBM Network Computing Software Division tie line 444-0736, outside 919-254-0736, email: ssadams(a)us.ibm.com <<Hebrews 11:6, Proverbs 3:5-6, Romans 1:16-17, I Corinthians 1:10>>

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An Education Argument for Squeak
by Mark Guzdial 28 Apr '98

28 Apr '98

Here's a hot-off-the-press result for those arguing with their department over whether to use Java or Squeak in their undergraduate courses. One of the particularly challenging topics in undergrad user interface software is Model-View-Controller. Lots of people (Jack Carroll, Randy Pausch, others) have written about the challenges that students have trying to understand such a system. I've been trying a whole bunch of different techniques over the last few quarters to help students learn this topic, from more live demonstrations, to teaching the individual pieces separately (changed/update separate from use in user interface systems). I've never got much more than an average of 50% on a midterm problem on MVC. This quarter I did something different: We "grew" MVC in class. Students are building three interfaces in class, and on none of these can they use library facilities for windows and buttons. Instead, they can only draw with Pens, display Forms, and read the Sensor. Now, they are faced with the question that MVC was meant to answer. During lecture two weeks ago, we "grew" MVC over the course of four iterations of a user interface. We started out by just blasting an interface up and dramatically modifying our model class. Then we separated out the buttons, then made them pluggable, then introduced changed/update and created pluggable textareas. We talked through creating Controllers and other kinds of components. What's important about this in the Squeak vs. Java argument is that it is very hard to do this kind of progression with Java, or just about any other language. Drawing without windows is a no-no, and grabbing raw user events is really tricky. But my hypothesis is that without facing the task of UI *without a toolkit*, students have a very hard time understanding how the toolkit works. Last week was the midterm exam, and again, I included a very similar problem to ones I've used before. Here are the results for the last four offerings of this course (grades normalized to between 0 and 1.0). Averages Sttdev CS2390Sp98 0.864705882 0.26834552 CS2390W98 0.539622642 0.34186272 CS2390Sum97 0.536170213 0.39902234 CS2390Sp97 0.441568627 0.36106493 Is the Spring 98 Quarter (now) *REALLY* better than Winter 98? I had the same grader and the same grading scale last quarter and this. I did a one-tailed T-test on the two sets of grades datas. p=4.4E-13 is much less than 0.05, so I think I'm safe claiming statistically significant difference. I plan to write a technical report on this soon, but I thought that y'all might be interested in some raw, early results. Mark -------------------------- Mark Guzdial : Georgia Tech : College of Computing : Atlanta, GA 30332-0280 (404) 894-5618 : Fax (404) 894-0673 : guzdial(a)cc.gatech.edu http://www.cc.gatech.edu/gvu/people/Faculty/Mark.Guzdial.html

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Any reference for Squeak
by Sunghun Seo (Sonny) 28 Apr '98

28 Apr '98

Is there any published reference book for Squeak? Or any reference paper on the Web? (only dedicated to Squeak) Cheers, Sonny Seo. PS. Is there someone who know when Sweak 2.0 will release?

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[Q] DO in Sqeak ?
by Chun, Sung Jin 28 Apr '98

28 Apr '98

Can I make Distributed Object as easy as NeXT PDO ? for exmaple; id proxy = [ NSConnection proxyFor...: "address.in.the.internet" ]; Or should I make whole framework for this ? Thanks in advance. ****************************************** I like N*Step's beauty, but Iove Freedom. ninja(a)aerohel.snu.ac.kr ---ObjC--- NSString* NSMyName = @"Chun, sungjin"; [ NSMyName fly ]; ---ObjC--- ******************************************

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