Self-interest November 2005

self-interest@lists.selflanguage.org

7 participants
8 discussions

Re: Self Objects
by sanssecours 30 Nov '05

30 Nov '05

--- In self-interest(a)yahoogroups.com, Jecel Assumpcao Jr <jecel@m...> wrote: > > sanssecours wrote on Tue, 29 Nov 2005 19:33:02 -0000 > > I have to write a little paper about self. I haven't programmed > > anything in Self or Smalltalk yet and only have a little experience in > > the mainstream programming languages out there (C,Java..). I think I > > already understand the "basics" of the Language. However there are > > some code samples on the Self-Homepage that I don't understand for > > example: > > Could you give a little more information about where you found this > example? There are a few things that are a bit strange about it. > > > (| x. y | > > x: 3.··y: 4. > > x squared + y squared) > > > > Ok as far as I know that sample shows an object with two slots that > > contain the objects x and y but what do the rest of the code mean. It > > seems like the code declares some method that returns x squared + y > > squared but whats the name of this method how can you use this method > > (in Java something like: Object.Method() - whats the corresponding > > code in Self). And what do the Points: "··" between x: 3 and y: 4 > > mean. It woul be very nice if sombeody out ther could help me. > > I should point out that the textual syntax became less important when > the graphical programming environment was introduced in Self 4.0 (1995) > though it is still very convenient for discussing code via email and > stuff like that. > > Your guess is correct - the syntax for an object or method is > > ( | slots | code ) > > where the "code" part is empty for regular objects (not the case above) > so they simply return themselves when accessed as a value in some slot. > Methods can have local slots like "x" and "y" in the example but they > also can have argument slots that don't make sense for regular objects. > On the other hand, having a method loose like that instead of defined in > some slot doesn't make any sense, as you also guessed. > > The two dashes before the "y:" could be a valid binary selector so the > code could be interpreted as > > set "x" to 3 > send "--" to self with the result of setting "y" to 4 as its argument > return the sum of the squares of "x" and "y" > > The second line seems *very* strange. If I had to guess I would say that > some text transformation(s) converted two tabs or similar formatting > whitespace into dashes. > > -- Jecel > Thanks for your quick response Jecel. It was very helful altough I have to admit that I really don't understand everything you wrote. Maybe the fault are my poor english-skills or maybe it is the rather complex syntax of self that's that is confusing me. Here is my short interpration of what you've written: "define a object with the two objects x and y." (| x. y | x: 3.··y: 4. "set the object x to 3, set y to 4" x squared + y squared) "return (x squared) + (y squared) " Could you please explain me why you have to send "--" to self ? Wouldn't this example without the "--" also work as expected and did i get this right: the method actually has no name ? How do you call the method ? The code for the sample was taken from the sun-website: http://research.sun.com/self/release_4.0/Self-4.0/Tutorial/Language/SyntaxA… Greetings (and thanks again :-) rene

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Self Objects
by sanssecours 29 Nov '05

29 Nov '05

Hello I have to write a little paper about self. I haven't programmed anything in Self or Smalltalk yet and only have a little experience in the mainstream programming languages out there (C,Java..). I think I already understand the "basics" of the Language. However there are some code samples on the Self-Homepage that I don't understand for example: (| x. y | x: 3.··y: 4. x squared + y squared) Ok as far as I know that sample shows an object with two slots that contain the objects x and y but what do the rest of the code mean. It seems like the code declares some method that returns x squared + y squared but whats the name of this method how can you use this method (in Java something like: Object.Method() - whats the corresponding code in Self). And what do the Points: "··" between x: 3 and y: 4 mean. It woul be very nice if sombeody out ther could help me. rene

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Re: [self-interest] dynamic inheritance (was: resend)
by J. Baltasar Garcia Perez-Schofield 14 Nov '05

14 Nov '05

Hi. Jecel > Normally each object is associated with a "map" that represents its type > to the virtual machine (pointers to maps are used in PICs and other > places). My change was to allow a single object to be associated with > more than one map (up to five) Interesting. Thank you for you answer. > Exactly. I call them "facets" since they are used a bit differently than > traditional mixins and reusing the name might cause some confusion. > These facets (sets of slots) are ordered so it is easy to see (literally > given the visual representation) which slot will match each message. If > Self were converted directly to such a scheme most objects would be huge > due to the globals but I don't have globals in the language, though the > programming environment has a catalog that does the same job (but at > edit time, not run time). I see. But are these facets "packed" inside the object, or do you have slots pointing to them ? Salud ! -- PBC -- J. Baltasar García Perez-Schofield jbgarcia en uvigo de es http://webs.uvigo.es/jbgarcia/ Dep. Informática, Universidad de Vigo, España (Spain)

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Re: resend (was: Multiple inheritance)
by rimerenu 11 Nov '05

11 Nov '05

Hello, all! As it is currently discussed I want to ask a question about the performance of Self VM. While I haven't done benchmarks, when I've run the Self VM (4.2.1) in Mac the user interface seemed to appear rather slow. The question is does just the user interface is slow or the Self VM is slow (for general application programming, not just scripting) despite the great efforts for optimization. Is current Self VM represents the final point in optimizations for a prototype based dynamic language or there is still room for substantial performance improvements. Regards, Emir Uner PS: I apologize if this mail comes twice because the first time I tried it failed.

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Re: [self-interest] resend (was: Multiple inheritance)
by J. Baltasar Garcia Perez-Schofield 11 Nov '05

11 Nov '05

Hello ! > > That's the point. > > But I suppose that this means that at runtime time, each time a > > resend/"unqualified" message is sent, and more than one parent is found > > for the receiver (and provided the receiver can't satisfy the message), > > then all inheritance paths are explored in order to avoid the > > possibility of finding more than one receiver (and show the debugger if > > found). > > Correct except for the "provided the receiver can't satisfy the message" > send the whole point of the resend is to skip any slots that the > receiver might have with that name. Mmmm ... note I wrote resend/unqualified messages: as far as I understood, "resend.copy" and "copy" would behave the same but for the lookup in "self" which would happend in the second case but not in the first one. > Michael Latta mentioned PICs and maps and other virtual machine tricks, > but I suppose that is what you mean by "the first time". Note that in my > example all three parents were constant slots. And probably their > parents too and so on. In such cases you can be sure that nothing will > change between the first and second times. I see. They are constant slots because they don't have an assignment slot. > If one of the parents had an associated assignment slot then you would > be correct: a lookup would have to be repeated on each message send. But > in practice such dynamic inheritance is rarely used. I actually came up > with a way to greatly speed up this situation but it didn't seem worth > the effort. And I eliminated this feature entirely from my own Neo > Smalltalk design. I'm very interested. My own virtual machine assumes that parent attributes can be changed anytime (not currently, sadly). http://trevinca.ei.uvigo.es/~jgarcia/TO/zero/ So maybe you could explain what exactly you thought as a solution. Although I am not working in that part of the VM, my first design to overcome this is to employ an observer pattern and make references observers of the attributes they must have to pass through in order to get to an object. Of course, another always-secure possibility is to recalculate a given reference each time it is employed :-). > As Self currently is this would be very likely since you add the slots > graphically and they are shown in alphabetical order. Yes, that's a problem. My VM also currently sorts members of each object alphabetically, I mean internally, though it doesn't offer multiple inheritance. > But for some > scripting language this might be an interesting option. In early > versions of Self/R I did have a depth first search exactly as you > suggest but around the time I changed the name to Neo Smalltalk I > decided to get rid of parents entirely and make the programmers manually > order the "facets" which make up an object. So you create your objects by joining mixins, perhaps ? Salud ! Baltasar -- PBC -- J. Baltasar García Perez-Schofield jbgarcia en uvigo de es http://webs.uvigo.es/jbgarcia/ Dep. Informática, Universidad de Vigo, España (Spain)

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Re: [self-interest] resend (was: Multiple inheritance)
by J. Baltasar Garcia Perez-Schofield 07 Nov '05

07 Nov '05

Dear Jecel: Thank you again for your explanation. > ( | parent* = traits clonable. > sharedStuff* = mixins utilities. "just an example - not in Self > distribution" > moreStuff* = mixins graphics. "another example" > subElements <- list copyRemoveAll. > copy = ( | new | > new: resend.copy. > new subElements: subElements copy. > new ). > ..... > | ) > > The "resend.copy" will do exactly the same (full) search that just > "copy" would have done except it will skip the local methods in the > object, which in this case is the very method doing the resend. Yes, as "super" in Java. > That > means that any copy slots in "parent", "sharedStuff" and "moreStuff" > will be found and if there is more than one then a debugger will pop up. That's the point. But I suppose that this means that at runtime time, each time a resend/"unqualified" message is sent, and more than one parent is found for the receiver (and provided the receiver can't satisfy the message), then all inheritance paths are explored in order to avoid the possibility of finding more than one receiver (and show the debugger if found). This can't be limited to the first time because Self is dynamic, the inheritance paths can change after a message is carried out due dynamic inheritance. So Self has to do it every time, and I guess this is quite expensive. Or maybe I am missing something ? The depth search is maybe problematic in some sceneries, but is obviously better in the best case (the receiver is found in the first inheritance path) and in the average case, though equal in the worst case. > An alternative would be to replace "resend.copy" with "parent.copy" (for > example) and in that case a "copy" slot in either "sharedStuff" or in > "moreStuff" More or less as in C++ with "SomeParent::foo()", I guess. Yes, I understand you can void any search by directly indicating the "inheritance path" you are interested in. > Some people prefer a depth first search but that has a nasty side effect > that just changing the order of "sharedStuff" and "moreStuff" in the > above code could change its meaning! Absolutely. However, is it likely to happen ?. I mean, if a programmer knows that order of parents in the parent list (whatever syntax you choose) has a meaning, would that programmer change the order of parents without noticing ? Regards, Baltasar -- PBC -- J. Baltasar García Perez-Schofield jbgarcia en uvigo de es http://webs.uvigo.es/jbgarcia/ Dep. Informática, Universidad de Vigo, España (Spain)

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Re: [self-interest] Re: Multiple inheritance
by J. Baltasar Garcia Perez-Schofield 07 Nov '05

07 Nov '05

Hi, Jecel ! Thank you for the info. However, > Self has always had two kinds of resends (like "super" in Smalltalk): > directed ones where you specify one parent to be search and undirected > ones with the word "resend" instead of a parent name which indicates > that all parents should be searched. Using the first kind you can work > around duplicated slot names but in the general case you will have to > refactor and/or rename things in your code to get it to work. In > practice this has proved to be much more usable than the original > automatic solution. So if a "resend" is performed, and all parents are searched ... is a depth lookup run or not ? Maybe a lookup in width ? Salud ! Baltasar -- PBC -- J. Baltasar García Perez-Schofield jbgarcia en uvigo de es http://webs.uvigo.es/jbgarcia/ Dep. Informática, Universidad de Vigo, España (Spain)

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Multiple inheritance
by std70 05 Nov '05

05 Nov '05

Hello! I'm Diego, a very beginner in self. Two questions: - Nowadays, has Self multiple inheritance? - If not, why Self lost this feature? Thanks Diego

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Self-interest November 2005