Beginners August 2006

beginners@lists.squeakfoundation.org

70 participants
71 discussions

collection enumeration
by cdrick 24 Aug '06

24 Aug '06

Hi all - not an important question here, more a discussion. I was wondering which method is the more appropriate (nice and/or efficient) to enumerate all the elements of a collection and the index of each elements... (a) ---- à la C (1 to: collection size) do: [:index | html render: 'Victime ', index printString. html render: collection at: index] (b) --- indexOf collection do: [:victim | html render: 'Victime ', (collection indexOf: victim) printString. html render: victim] (c) ---- keysAndValuesDo: collection keysAndValuesDo: [:index :victim | html render: index printString. html render: member] (d) ---- using a local var | index | index := 0. collection do: [:victim | index := index + 1. html render: 'Victime ', index printString. html render: victim] What solution would you suggest ? I think we forget (a) and (d) I like (c) but maybe (b) is more readable ? Maybe there is another way ? Thanks Cédrick

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Equiv. ruby's method_missing
by Bakki Kudva 23 Aug '06

23 Aug '06

Hi all, Rail's Activerecord uses Ruby's method_missing to implement dynamic finders such as find_by_#column_name() which is done by defining in the receiver... def method_missing(method_id, *arguments) if match = /find_(all_by|by)_([_a-zA-Z]\w*)/.match(method_id.to_s) finder, deprecated_finder = determine_finder(match), determine_deprecated_finder(match) attribute_names = extract_attribute_names_from_match(match) super unless all_attributes_exists?(attribute_names) <snip> Does Smalltalk have some way of emulating this? I am reading Smalltalk-80 books and don't see anything there. Is the current language support such callback hooks (and others which trap object create events and such?) I was inspired to study this when I read an old thread (2005) on the seaside list about writing an activerecord like layer for Seaside...although GLORP may be a better option in the long run. This is pretty much an academic excercise for me now. THanks for your help, bakki

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Squeak : text description of the stack for bugs?
by florent trolat 23 Aug '06

23 Aug '06

Why can I have a text descritpion of the stack when I have a bug? :-( thanks :-)

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RE: [Newbies] Changing error message
by Ron Teitelbaum 22 Aug '06

22 Aug '06

Hi Sedar, Welcome to the list. Before giving you and explanation let me say that if there is anything I mention which you do not understand please feel free to ask questions. There are a few things to understand about exception handling. First is that there is a class called Exception. Have a look at the hierarchy of the class. There are two parts to exception handling. There is the error itself, and then there is the exception handler. An error is signaled (sometimes called raised). The handler catches the error and handles it. Notice in the hierarchy that there is a class Error. This is usually where you want to start for errors in code because if you wrote a handler for Exception you would prevent errors, or handle errors yourself that you would rather the system handle. Things like halt are a good example. When an exception is signaled the system looks in the calling stack for a handler. A handler could that used the class of the exception or any of its superclasses can handle the error. For example if I have a: Error subclass: #MyGeneralError And MyGeneralError subclass: #MyNoDigitError Then if the code does MyNoDigitError signal: 'You should have more then one digit here. Thank you' Then if you have a handler for #MyNoDigitError or #MyGeneralError or both, it will execute the handler for which ever one comes first in the stack. Ok I'm glad you made it this far stick with me and then I'll give you an example which should help to make it clear. For a stack to have a handler the code that you are executing needs to have an exception wrapper. In other words you need to wrap the code that you think might signal an error. To wrap the code you put your code in a block and then add the Error class and the handler. [self myCode] on: MyNoDigitError do: [:ex | self myHandlerCode]. [A little aside. You can skip this part if this is already too complicated. What I like to do is code my handlers on my exception class so instead of self myHandlerCode I use ex myHandlerCode. The ex is an instance of your error class so you can put code right on that class to do what you want. Also you can use tag to add more information on your class like the instances you need to operate on. You can even add additional ivars to your exception class to hold what ever you want. The benefit of this is that all your exception handlers are in one place so it's easy to find and reusable!] Ok so examples: First something that just works. Create the classes above MyGeneralError and MyNoDigitError Notice that both of these work. [MyNoDigitError signal] on: MyNoDigitError do: [Transcript cr; show: 'Hey I hit an error']. [MyNoDigitError signal] on: MyGeneralError do: [Transcript cr; show: 'Hey I hit an error']. Now it's time to use your imagination. Because this is a very primitive example you have to actually imagine using it. Imagine a method. ATMMachine >>depositAmount: anAmoutToDeposit "return to the sender aBoolen which represents the acceptance or rejection of anAmountToDeposit. When accepted the receiver will forward anAmountToDeposit to the authenticated users selected bankAcount where it is placed on hold until anAmountToDeposit is verified" self userIsAuthenticated ifFalse: [ATMLoginError signal: 'User has not been authenticated'. ^false]. self selectedBankAccount ifNil: [ATMNoSelectedBankAccount signal: 'Please select an account to deposit too.'. ^false]. anAmountToDepost hasDigits ifFalse [^MyNoDigitError signal: 'I can only deposit numbers'. ^false]. self selectedBankAccount holdDepositForVerification: anAmountToDeposit. ^true Ok well that handles the error signaling the error. Now we need to wrap it. ATMMachine >> deposit "request amount to deposit and perform depositAmount" anAmountToDeposit := self getAmountFromUser: 'How much did ya want to deposit?'. [self depositAmount: anAmountToDeposit] on: ATMLoginError, AtMNoSelectedBankAccount, MyNoDigitError do: [:ex | self cutUpUsersAtmCardAndBlowRasberriesAtThem]. So now you can see that if the user does something wrong we handle the error. Notice that the errors are raised up the stack in depositAmount: but the handler is executed in deposit method. This is very useful for some very interesting but very hard to read hacks. If someone is interested please let me know. Ok so now to answer your question. Thought I'd never get here huh, if you want to change the way an exception is raised you need to insert your own handler before the default one catches it. Try this: Execute the following in a workspace: 10/0 Notice that the error class is ZeroDivide. You can intercept the handler by doing this. [10/0] on: ZeroDivide do: [:ex | ex signal: 'Dividing by zero could destroy the universe']. Since you provided your own handler in the stack before the regular handler could catch it you changed the message. Please feel free to ask questions. Happy coding! Ron Teitelbaum President / Principal Software Engineer US Medical Record Specialists Ron(a)USMedRec.com > From: Serdar Sahin > Sent: Thursday, August 03, 2006 5:38 AM > > Hi, > > Is it possible to change some error messages ? For example, if i get > "Error: At least one digit expected here" error, i want to show my own > error message. Is that possible ? > > Thanks,

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Re: [Newbies] Building the equivalent of wget in Squeak
by andy.burnett＠knowinnovation.com 22 Aug '06

22 Aug '06

Brilliant, that is just what I was looking for. I just hadn't been looking in the right places. Thanks very much. <<You can use something like (HTTPClient httpGet: 'www.google.com') contents to get the text of a web page. Just using HTTPClient httpGet: 'www.google.com' gives you a "stream" over the page's text. You can browse HTTPClient's class side to see how the method works and start digging deeper. Hope this helps, Benjamin Schroeder>>

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FFI, pragma and co...
by cdrick 22 Aug '06

22 Aug '06

Hi As some of us, I'm following the two lists (dev and beginner..) and there is a long interesting discusion about pragma, FFI, primitive... but I don't really know them ;) exept what I found on wikipedia lol Can anyone indicate me pointers or maybe simple examples to understant that better ? in general for the extension mechanism < > This is something I found "strange" when I first see them in smalltalk where everything is an object ;). Primitives are objects ? Thanks in advance Cédrick ps: I'm interested in Pragma as it's a kind of metadata as far as I have understood. But how to use them ?

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Re: Beginners Digest, Vol 4, Issue 34
by andy.burnett＠knowinnovation.com 22 Aug '06

22 Aug '06

Thank you gentlemen @Damien you are quite right, networking may be too difficult to begin with. It is just that in some languages, e.g. Rebol, fetching http is trivially simple. I was hoping it might be similar in Smalltalk. @Stephane. Thanks, I shall go and look directly. Cheers AB

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Building the equivalent of wget in Squeak
by andy.burnett＠knowinnovation.com 21 Aug '06

21 Aug '06

Hello I would like to create a simple means of getting the contents of a web page, in the same way that wget works. What I hoped to do was something like: wget url: 'http://...' show. I found a few classes e.g. Httpurl and also the asUrl method of the string class, but I can't quite work out how to put it all together. As it seems like a simple way to start learning Squeak, I wonder if someone could point me in the right direction. Thanks AB

4 3

Collection>>Includes:...
by florent trolat 21 Aug '06

21 Aug '06

Hi, I've define an '=' message for an oject and I want to use this object in a Collection. I've seen that 'incudes:' message use '=' or not '==' and it's not fun for me! I think that '=' message is to compare two objects and '==' to know if the two object are one! So for me 'includes:' must use '==' or not '='... May be I have not understand something... Thanks to help me....

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Squeak dev mailing list : advertising or new game ;-)
by florent trolat 20 Aug '06

20 Aug '06

Hi, sorry to disturb you... but I've received a lot of odd mails on the sqeak dev mailing list. Maybe it's advertising for a new TV soap... ? ;-) I think you can send your ideas to change the end! ok I go to bed, it's a depressing joke... :-( PS: don't forget : "A friendly place...." :-) :-) :-)

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Beginners August 2006