Squeak-dev February 1998

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by Alek 09 Jun '00

09 Jun '00

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Re: Re: Float bug toolkit: what the hash is this?
by Tim Olson 31 Aug '99

31 Aug '99

>>"[1]" (10 raisedToInteger: 600) = (10.0 raisedToInteger: 800) "alt-p" >>These are equal since both expressions end up answering a float with a >>special value indicating positive infinity. Positive infinities are always >>equal. > >Nonono.... (10 raisedToInteger: 600) is anInteger, while the other (if >finished correctly) is aFloat. Correct. The problem occurs when the #= message is sent to the LargePositiveInteger with the argument a Float (+Infinity). This causes the LargePositiveInteger to be adapted to a Float (resulting in +Infinity, as well). >If aFloat turns out to be infinite, an error >should be posted. This would have to be tested in the Float primitives in the VM whenever an overflow (or NaN, I suppose) is generated. However, I *think* (VM experts correct me, here) that all they can do is fail rather than returning a succesful value, so all of the Float code that invokes primitives would have to be rewritten to test and reflect this overflow/exception failure. The IEEE "default" operation is to silently return the default values (Inf or NaN), rather than generating an exception. What should the standard for Squeak be? -- tim

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Re: Sending WinSqueak Code: Dumb but Critical Question
by guzdial＠cc.gatech.edu 26 Aug '98

26 Aug '98

>You may try the attached CrLfFileStream which automatically detects the >actual line end convention of a file. To install it for permanent use >change FileStream class>>concreteStream to return CrLfFileStream rather >than StandardFileStream. > >Hope this helps, > Andreas Works great, Andreas! Thank you! My students are filing it in as a I type... 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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Re: class, prototype, meta
by David Farber 02 Mar '98

02 Mar '98

>But I think a critical point here is that just being able to clone willy-nilly >is confusing one metalevel with another -- and here is where I disagree with >the "Lieberman" and SELF (what I think of as the LISP, or "data structure") >schools of prototypes. I feel it is very important to at some point make a >commitment to "kind" (I use this word because better terms like "type" and >"class" have already been colonized with too-specific meanings in the computer >world). So, while I think that you should be able to do absolutely anything >with and to your programming system, I also think there should be "guardians at >the gates" when you go from one metalevel to another. E.g. it shouldn't be as >easy to change the inheritance chain as it is to send a safe message to another >object. > > An analogy is that one of the reasons we put in encapsulation and tried to >get rid of data structures is because an assignment statement is a different >metalevel than a function call, and you just should not be able to do either >equally easily. Our initial idea was to at least confine the dangerous >assignments while we were learning how not to need them. Obviously, allowing >the equivalent of easy assignments to deep structural elements (like >inheritance pointers, etc.) is a worse idea. The first Smalltalks also allowed >"no overhead" syntax definitions -- it was an integral part of programming. >This gave us an easily extensible language on all fronts of syntax, semantics >and pragmatics, but turned out to be a bad idea for the same reasons. In >Smalltalk-76 we perhaps reacted too much in the opposite direction, and didn't >put a more appropriate meta-level in the language for defining syntax -- but >the earler way we worked simply led to a tower of Babel. okay, i am trying to keep up here. how is an assignment on a different metalevel than a function call. since you made the assertion, i can certainly see where you are headed, but what is critera for a metalevel? > But it is really terrible if you just ban such things. That is too >moralistic and smacks of the Wirth school of (non)programming. This is why well >thought out metasystems should allow the good designer/programmer to have their >cake and eat it too. The "Metaobject protocol" by Greg and Danny, et. al., at >PARC is an inspiring further advance in what we had done there in the '70s, and >it gives some tantalizing insights into what could yet be invented.... you mentioned this book in your oopsla keynote, but i haven't been able to get my hands on it. to be honest, i haven't tried that hard to get it because you remarked that it was probably only comprehensible to someone with an extensive Lisp back ground (which ain't me) and it really needed to be rewritten for Object Land at large (for which, i believe, you offered a second Smalltalk balloon like the one you gave Dan). so, since *you* read it and seemed to get a lot out of it, why don't you clue the rest of us in on some of its more salient points and how you think we might be able to translate them in squeak (or the next blue thang). thanks, dave -- j. david farber oo architect+mentor numenor labs incorporated in sunny boulder colorado dfarber(a)numenor.com www.numenor.com

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class, prototype, meta
by jecel＠lsi.usp.br 28 Feb '98

28 Feb '98

"Alan C. Kay" <alank(a)wdi.disney.com> wrote: > But I think a critical point here is that just being able to clone willy-nilly is confusing one metalevel with > another -- and here is where I disagree with the "Lieberman" and SELF (what I think of as the LISP, or > "data structure") schools of prototypes. I feel it is very important to at som e point make a commitment to > "kind" (I use this word because better terms like "type" and "class" have alre ady been colonized with > too-specific meanings in the computer world). So, while I think that you shoul d be able to do absolutely > anything with and to your programming system, I also think there should be "gu ardians at the gates" when > you go from one metalevel to another. E.g. it shouldn't be as easy to change t he inheritance chain as it is to > send a safe message to another object. It is possible to change the inheritance graph with a simple message in Self if you use "data parents". But nobody does this as the current implementation can't deal very well with it, so performance suffers considerably (besides, it hasn't been as useful as people would thought it would be). Other than that, changing objects and their inheritance structure is pretty "heavyweight" compared to "safe" messages. You have to creeate a mirror and navigate through it and so on. Of course, the programming environment hides all this meta-level by allowing you to drag-n-drop slots from object to object. But it still feels very different than sending messages. The problem with Self is that it hides its meta-level in the implementation as much as possible. The notion of "kind" as reified in C++ objects called maps is totally out of reach of the Self programmer. Several applications suffer a lot from this, like Ole Agesen's type inference stuff and Mario's Smalltalk emulator. I love simplicity, but wouldn't trade structured programming for GOTOs :-) -- Jecel

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Re: class, prototype, meta
by David Farber 28 Feb '98

28 Feb '98

(nice to see you back on the list, Jecel. tudo bem? é mutio frio aqui, viu? pensei ontem á noite que necessito ir a Brasil prá cambiar o inverno con o veraõ! outra coisa: que é a diferencia entre necessitar e precisar? quando devo usar uma em lugar da outra?) At 01:34 PM 2/28/98 -0600, you wrote: >David Farber <dfarber(a)numenor.com> wrote: >> i really like the idea of adding prototypes to squeak, but is there a way to >> add prototypes *and* keep classes? > >I would say Mario Wolczko already proved this could >be done when he implemented his Smalltalk emulator >in Self. You can read about it if you start from the >Self mirror, choose "this release" and then >"documentation". The mirror is at: > >http://www.cs.ucsb.edu/oocsb/self/index.html > >Of course, this Smalltalk system is pretty "shallow" >compared to Squeak and isn't as well integrated with >Self as it could be, but it does show that prototypes >and classes can live just fine in the same system. i knew that a Smalltalk system had been written in Self. it seems fairly evident that Class is a subset of Prototype. my questions is, if you were to get your hands on one of the "Smalltalk" object instances from somewhere else in the Self system, could you manipulate that instance as if it were a "Self" instance (i.e. add a slot)? i would want this to be illegal, or rather, thwarted by the meta facilities. dave -- j. david farber oo architect+mentor numenor labs incorporated in sunny boulder colorado dfarber(a)numenor.com www.numenor.com

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class, prototype, meta
by jecel＠lsi.usp.br 28 Feb '98

28 Feb '98

David Farber <dfarber(a)numenor.com> wrote: > i really like the idea of adding prototypes to squeak, but is there a way to > add prototypes *and* keep classes? I would say Mario Wolczko already proved this could be done when he implemented his Smalltalk emulator in Self. You can read about it if you start from the Self mirror, choose "this release" and then "documentation". The mirror is at: http://www.cs.ucsb.edu/oocsb/self/index.html Of course, this Smalltalk system is pretty "shallow" compared to Squeak and isn't as well integrated with Self as it could be, but it does show that prototypes and classes can live just fine in the same system. -- Jecel

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class, prototype, meta
by David Farber 28 Feb '98

28 Feb '98

i really like the idea of adding prototypes to squeak, but is there a way to add prototypes *and* keep classes? what i would like to see is a meta object protocol that had the flexibility to facilitate both modes of "sharing" (to put it terms of the Treaty of Orlando). could we pull something like this off? you guys at Disney have hinted about changes to the meta model; have you thought about anything like this? dave j. david farber oo architect+mentor numenor labs incorporated in sunny boulder colorado dfarber(a)numenor.com www.numenor.com

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Re: auto-delegate messages
by Eliot & Linda 28 Feb '98

28 Feb '98

Tim Olson wrote: > > Hi, all: > > Here's a cute trick / crufty hack I recently posted to > comp.lang.smalltalk. It was in regards to someone complaining that they > had to recreate a bunch of methods when using a delegate to implement > multiple-inheritance-like operation. Instead of manually doing this > (painful) or dynamically doing this by implementing doesNotUnderstand: > (slow), why not combine the two and have the doesNotUnderstand: method > install the custom-created method? > > Comments? The technique was the basis of Dan Ingalls' and Allan Borning's multiple inheritance system for Smalltalk-80 v2.0. An instance of a class with multiple superclasses checked its extra superclasses for methods in doesNotUnderstand: and recompiled them in its own class so that the next time it was sent there would be no doesNotUnderstand:. The scheme maintained a dependency graph so that if one changed a method (either modified or deleted) that was copied all the copies would be removed. When a class with multiple superclasses was first created for all selectors that had more than one reachable implementation, i.e. ambiguous methods, the class would create a method that did ^self conflictingInheritanceError. The programmer could then resolve the ambiguities as required. The implementation was buggy; self was not renamed when copying down; conflicting inheritance methods overrode the resolutions if you redefined the class; redefining superclasses could cause bugs due to the traversal machinery expecting a tree and not a graph, etc. Evewn with these bugs fixed the general feeling was that it was too complex. The best alternative I've seen is Gilad Bracha's mixin-based multiple inheritance scheme. http://java.sun.com/people/gbracha/mwp.html _______________,,,^..^,,,_______________ Eliot Miranda

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Formatting methods needed
by James Messick 28 Feb '98

28 Feb '98

Does anyone have some methods to return formatted strings? Specifically I'd like to format numbers with a specific number of decimal placed (5.000). I'd also like to produce formatted dollar strings ($1,233.45). Tanks! _________________________________________________________ DO YOU YAHOO!? Get your free @yahoo.com address at http://mail.yahoo.com

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