Squeak-dev June 2004

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154 participants
393 discussions

Re: [ENH] CharacterTimes-rsb
by Richard A. O'Keefe 25 Jun '04

25 Jun '04

Stephan Rudlof <sr(a)evolgo.de> wrote: I second this. It takes time to read your mails, but it takes a lot more time for you to write them! Thank you. For me recently the Set/hash discussion was illuminating, especially the point, that a Set shouldn't contain itself in the world of actual programming languages. My first thought about this has been mathematically (where a Set may include itself, if I remember correctly). I really want to take all the sting out of this, but I'm afraid you haven't remembered correctly. If you're fairly comfortable with mathematics, a book that I found extremely helpful is The Joy of Sets : Fundamentals of Contemporary Set Theory Keith Devlin Springer-Verlag 1993 ISBN 0387940944 List price, about USD50, you can get a used copy over the web for USD35. A core feature of "standard" (Zermelo-Frankel or Goedel-Bernays) set theory is that the universe of sets is WELL-ORDERED. There are no infinite chains x0 \in x1 \in x2 \in ..... The way Devlin explains this in The Joy of Sets is by constructing the ZF universe as a transfinite sequence of "layers", such that a set in some layer may only contain elements from strictly earlier layers. The bottom layer is the empty set. The fact that there are no infinite descending chains is incredibly important, because it means that you get to use proof by induction. The programming language analogue of this is that you get to use loops and recursion. Take this little loop: x := aSet. [x isKindOf: Set] whileTrue: [x := x anyOne]. When can we expect this loop to terminate? When aSet is well-founded with respect to #includes:. Now, Peter Aczel has written a book "Non-well-founded Set Theory". I even have a copy of it. To be honest, past chapter 1 I didn't really understand much of it, only enough to decide I didn't really need it. The Joy of Sets has a discussion of non-well-founded set theory near the end. But it's still true that when mathematicians talk about "sets" (as opposed to "non-well-founded sets") they mean ZF or GB -- which describe the same sets using different axioms -- or either of those extended with atoms that are not sets. Now there are excellent reasons to construct graph structures in programming languages. Mathematicians talk about graphs as pairs of sets (Nodes, Edges), but in a programming language it may be more convenient to think of a set of Node objects (this set does not point to itself) with each Node having a set of Nodes that it is connected to, so that the pointer graph of node -> neighbour set -> node DOES have cycles, and the collection of Nodes is NOT well-ordered under #hasSuccessor: . The loop x := aNode. [x neighbours isEmpty] whileFalse: [x := x neighbours anyOne]. may well not terminate. "Loop terminates" if and only if "stepping relationship is well founded", so knowing when a relationship is well-founded is of great practical interest to programmers. One point did come up in this discussion which no-one seems to have picked up, and it does have important practical consequences for Squeak (or any other Smalltalk-like language) and we might need to think about a change to #= and #hash to deal with it. I'm going to run this example in Ambrai Smalltalk. I _like_ Ambrai Smalltalk, although I must say that the main thing I have learned from it is how much I prefer the Squeak IDE. Create a Workspace window, type |x| x := Array with: 1. x at: 1 put: x. x hash then Cmd-A Cmd-D (this would be Cmd-P in Squeak) and wait for a while. Ka-BOOM! Ambrai Smalltalk softly and suddently vanishes away. The reason is IndexedCollection>> hash |size hash| size := self size. hash := "doesn't matter" ^size <= 5 ifTrue: [ 1 to: size do: [:i| hash := "a function of hash and (self at: i)"]. hash] ifFalse: [ "doesn't matter" ] So to compute x hash, it tries to compute x hash, to compute x hash, ... and when the stack overflows, Ambrai dies. Squeak has a different and in some ways better hash function: SequenceableCollection>> hash |hash| hash := self species hash. 1 to: self size do: [:i | hash := "a function of hash and (self at: i)"]. ^hash It has the same problem. The important difference is that Squeak catches and can recover from stack overflows. I spent a long time preparing a Lisp example to show that (sxhash xobject) should work for cyclic objects, but in the two Common Lisp implementations I tried, it didn't. (I had to get a technician to show me how to turn my new eMac back on again. This was rather humiliating.) If you think about it, this is not altogether unreasonable: the point of hash functions is that (equal x y) ===> (= (sxhash x) (sxhash y)) so that if (equal x y) -- or for us, x = y -- isn't going to terminate, it doesn't matter that (sxhash x) -- or for us, x hash -- isn't going to terminate either. But suppose we do this: |s| s := Set new. 1 to: 10 do: [:i| |a| a := Array with: i with: nil. a at: 2 put: a. s add: a]. Here we have a case where x = y is going to terminate quickly, but x hash will not terminate and neither will y hash. There are several ways to work around the problem. One of the simplest is this. Object>> hash ^self hashToDepth: 8 hashToDepth: d ^0 < d ifTrue: [userHashToDepth: d-1] ifFalse: [self class identityHash] userHashToDepth: d ^self identityHash Then replace all hash .... x hash .... methods with userHashToDepth: d .... (x hashToDepth: d) .... methods, or, if the class is such that objects _cannot_ be cyclic, such as numbers, bitmaps, strings, unboxed arrays, and so on, retain the existing #hash methods and add userHashToDepth: d ^self hash This doesn't stop hashing taking an unreasonably long time, but it does mean that it will terminate (if I haven't made any silly mistakes). This would handle my example of a Set of arrays each of which has a distinct first element (but is cyclic via its second element). Even without cyclic structures, a depth-bounded hash can be useful because it reduces the amount of work done for large trees. That leaves us with the problem of defining #= for cyclic data structures. This has actually been solved by Prolog implementors, or at least, implementors of the ISO Prolog standard. In Prolog, L = [1|L] makes L a cyclic list of ones. In "classic" Prolog, L = L could then loop. In ISO Prolog, L = L must terminate (and should of course say "yes"). The method goes something like this: to determine whether x and y are equal: determine whether x and y are equal assuming {} to determine whether x and y are equal assuming equalities if x or y is an immediate value, determine equality by that way. if x and y do not have the same constructor, report that they are not equal. if (x = y) is amongst the assumed equalities, report True. otherwise, let equalities' = equalities U {x = y} for each corresponding component xi of x, yi of y determine whether xi and yi are equal using equalities' if they aren't, report False. Something like this could obviously be programmed in Smalltalk, with = anObject calling equals: anObject assuming: equations and that calling userEquals: anObject assuming: equations. I'd rather not think about it. What this means for us as Smalltalk programmers is that (a) Smalltalk *could* have been designed so that #hash and #= supported cyclic objects. It wasn't. This isn't surprising. The original Smalltalk-80 used reference counting, so you really were NOT supposed to have cyclic objects at all anyway. Trying to put a Set inside itself would have been a big No-NO on garbage collection grounds. (b) We could change Squeak so that it does handle #hash and #= for cyclic objects. That would be a lot of work, and a lot of examples in Smalltalk books would need changing. But unless and until #hash and #= _are_ changed suitably, (c) If we design some classes so that object cycles may occur, we should be very careful about #= and $hash. In the case of such a cyclic graph of objects, the default implementations of #= and #hash inherited from Object may be just right. I don't mean just "pragmatically useful", I mean "correct". In such a case the object identity often really is part of what it represents. But sometimes we have objects that belong to (classes that inherit from) system classes with _other_ definitions of #= and #hash, and then we must be very careful to break the cycles. (d) Even if we fix #= and #hash, the assumption "there are no cycles" is deeply embedded in a lot of Smalltalk code. Such as #deepCopy and #printOn:. Putting objects inside themselves is dangerous...

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[FIX] [3.6] PoohSubdivisionCreationFix-nk
by ned＠squeakland.org 24 Jun '04

24 Jun '04

from preamble: "Change Set: PoohSubdivisionCreationFix-nk Date: 23 June 2004 Author: Ned Konz The Balloon3D version shipped with the 3.6-Full image broke Pooh painting. This change set restores the use of Pooh painting. "!

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SM problems (Internal Server Error)
by Ragnar Hojland Espinosa 24 Jun '04

24 Jun '04

http://map1.squeakfoundation.org/sm/recentnew Internal Server Error MessageNotUnderstood: HVHtmlBuilder>>linklocal:text: Comanche/6.2 (unix) Server at 62.4.94.149 Port 8080 Link is from squeak swiki (freshmeat) -- Ragnar Hojland - Project Manager Linalco "Specialists in Linux and Free Software" http://www.linalco.com Tel: +34-91-4561700

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[ANN] Ambrai Smalltalk on mac OSX
by stéphane ducasse 24 Jun '04

24 Jun '04

Welcome to this new smalltalk that was not really advertised :) http://www.ambrai.com/smalltalk/ Stef

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REMINDER: Harvesting Party Friday June 25th 13:00 GMT
by Ken Causey 24 Jun '04

24 Jun '04

Just a reminder that the next Harvesting Party will take place between 13:00 (1 PM) and 17:00 (5 PM) GMT Friday June 25th, 2004. As usual we will meet in #squeak on irc.freenode.net. More information about the #squeak IRC channel can be found at http://people.squeakfoundation.org/article/7.html Information about the Harvesting Party idea can be found at http://people.squeakfoundation.org/article/29.html If you have the time please attend and work toward the future of Squeak. The next seven parties are scheduled for 17:00 (05:00 PM) GMT Tuesday June 29, 2004 21:00 (09:00 PM) GMT Saturday July 03, 2004 01:00 (01:00 AM) GMT Thursday July 08, 2004 05:00 (05:00 AM) GMT Monday July 12, 2004 09:00 (09:00 AM) GMT Friday July 16, 2004 13:00 (01:00 PM) GMT Tuesday July 20, 2004 17:00 (05:00 PM) GMT Saturday July 24, 2004

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SqueakSource server not running
by Frank Shearar 24 Jun '04

24 Jun '04

Is it just me or has the SqueakSource server disappeared? Nothing's running on kilana.unibe.ch:8888. Other servers on kilana run though, like kilana.unibe.ch:9090 (the SmallWiki wiki). frank

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[FIX] NewParagraphComposeFix-nk
by ned＠squeakland.org 24 Jun '04

24 Jun '04

Please also look at BFAV IDs 22934, 22935, 22594, 22752, and probably others. "Change Set: NewParagraphComposeFix-nk Date: 23 June 2004 Author: Ned Konz We have had the problem in the past with broken text morphs being distributed in the image. These lived in some flap tabs, and caused problems with saved projects and new projects. This change set adds a guard in NewParagraph to avoid the problems caused by the (uncommon) case of a paragraph with inconsistent state. "

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Dynamically changing the shape of a class
by Alexandre Bergel 23 Jun '04

23 Jun '04

Hi! Adding new instance variable is done by calling a become: like oldclassWithoutTheNewIV become: newclassWithTheNewIV Therefore this operation requires some primitive in the VM. Is it necessary? If this mechanism is not implemented in Java is it only because the VM does not have a become: ? Cheers, Alexandre -- _,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;: Alexandre Bergel http://www.iam.unibe.ch/~bergel ^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;.

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SHOUT request for new preference
by Stéphane Rollandin 23 Jun '04

23 Jun '04

Hello, I would like to suggest a small change in SHOUT settings. While SHOUT is an extraordinary tool in browsers, it may be somewhat intrusive in workspaces: often I use a workspace to display some text which is not code at all. When SHOUT is enabled, such text gets wrongly syntax-highlighted. While the best way to deal with this would be I guess to define a per-workspace setting (such as the existing 'create textual reference to dropped morphs' toggle), it would be nice to at least have a specific setting for disabling SHOUT in workspace, having Workspace>>stylerAboutToStyle: use Preferences syntaxHighlightingInWorkspaces instead of Preferences syntaxHighlightingAsYouType ... and then I think Preferences syntaxHighlightingInWorkspaces should default to false. does this make sense ? regards, Stef

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how to set codeUrl when publishing a project
by kwiyi woo 23 Jun '04

23 Jun '04

Hello, I want to publish my project on-line on my own webserver. It was written in Squeak programming language. I did a simple test, but it failed. The whole c1.html is as follows <html> <head> <title>Squeak Plugin Launcher</title> <base href="www.squeakland.org"> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> </head> <body bgcolor="#FFFFFF"> <object id="SqueakOCX Control" width="752 height="450 type="application/x-squeak-source" classid="CLSID:2BE9C39E-8386-4435-B337-FCDAD8EAB006" codebase="http://squeakland.org/installers/SqueakPluginInstaller.exe"> <param name="src" value="http://localhost/~Qinyi/c1.sts"> <param name="codeUrl" value="http://localhost/~Qinyi/Test.st"> <param name="projectUrl" value="http://localhost/~Qinyi/c1.001.pr"> <param name="pageId" value="43"> <param name="locked" value="false"> <param name="types" value="text-survey"> <param name="pluginspage" value="http://www.squeakland.org/detect.html"> </object> </body> I put the project starting command in the file c1.sts and set the value of src to it. ----------------------- c1.sts -------------------------------- | c1 | c1 _ C1 new. ----------------------------------------------------------------------- I filed out the project resource in Test.st and set the value of codeUrl to it. ----------------------- Test.st -------------------------------- Morph subclass: #C1 instanceVariableNames: '' classVariableNames: '' poolDictionaries: '' category: 'Test'! !C1 methodsFor: 'initialization' stamp: 'w 6/23/2004 11:45'! initialize | r | r _ RectangleMorph new. r openInWorld.! ! ----------------------------------------------------------------------- Finally, I save the project as c1.001.pr and set the value of projectUrl to it. But when I browsed c1.html through IE, it said that MessageNotUnderstood: new The problem is that the squeakplug in cannot find the definition of C1 defined in codeUrl. Is there anyone who can help me figure out the right configuration to it? Thanks Kwiyi --------------------------------- Do you Yahoo!? New and Improved Yahoo! Mail - 100MB free storage!

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