[Pharo-dev] Opal hook?

Stéphane Ducasse stephane.ducasse at inria.fr
Thu Dec 5 02:38:50 EST 2013


Hi nicolas

> I forgot to add that the OCUndeclaredVariableWarning was already handled at semantic analysis.
> Do you suggest that default behavior should be to handle and retry instead of handle and return?

I suggest that we can define what is the behavior of handling an exceptional cases. 

> One way to achieve what you are asking would be to initialize the Undeclared entry to some kind of ProtoObject that does not understand anything and rethrow a OCUndeclaredVariableWarning instead of a MessageNotUnderstood... (very uneasy to debug, since the Debugger itself is querying the receiver etc... - unless Debugger is using basic mirror primitives)

we should be able to say:
	when you encounter an undefined do that
	when you enconter a syntax error do that

We should have a list of hooks and exceptional situations and be able to define the actions we want to be performed.
This way the compiler would not depend on the UI also :). I love these "layers" from the past. 
When you have a UI then you specify new actions which involves popup and other niceties.

and in particular exception should not hardcode the popup of menu and other UI related things. 
So this is not linked to the phases of compilation, this is linked to offering customisable error. 
Stef

> 2013/12/4 Nicolas Cellier <nicolas.cellier.aka.nice at gmail.com>
> Steph, each time you want to evaluate something, do you agree that this involves
> - a parse phase of the expression you want to evaluate to create an AST
> - a code generation phase from AST -> bytecodes to generate a CompiledMethod
> - the evaluation phase itself which evaluates above CompiledMethod with appropriate receiver (nil generally)
> 
> I didn't check OPAL, but do you agree that the semantic analysis determining which are those variables you called {'AnUnknownClass'. 'OCUndeclaredVariableWarning'. 'self'} and how to bind them, must happen somewhere between AST and CompiledMethod creation?
> 
> So if there is a semantic exception, like UndeclaredVariable, how would the CompiledMethod be generated in the first place?
> If it's not generated, how would it be executed?
> If it's not executed, how would the message on:do: be sent to a block with 2 arguments?
> 
> Unless you suggest to attempt executing a ParseTree which is known to be defectuous...
> 
> 2013/12/4 Stéphane Ducasse <stephane.ducasse at inria.fr>
>> AnUnknownClass subclass: #Adaptor1Example
>>         instanceVariableNames: 'customers accountID address name phoneNumber'
>>         classVariableNames: ''
>>         poolDictionaries: ''
>>         category: 'Examples-Cookbook'
>> 
>> executes the default action for OCUndeclaredVariableWarning, which is opening a pop-up titled: "Unknown variable ...". Here the error is raised at compilation time, therefore it would have no effect to wrap this with a #on:do: 
> 
> I do not understand why if an exception is raised why I cannot trap it. 
> 
> [AnUnknownClass subclass: #Adaptor1Example
>         instanceVariableNames: 'customers accountID address name phoneNumber'
>         classVariableNames: ''
>         poolDictionaries: ''
>         category: 'Examples-Cookbook'] on: OCUndeclaredVariableWarning do: [ self halt.]  does not halt. 
> 
> The fact that is is at compilation time does not mean anything to me. So why? I'm totally confused by this bad and unexpected behavior. 
> Do you imply that the warning is already trapped and that I cannot take precedence? Probably but this has nothing to do with compilation time.
> 
> Then to me OCSemanticWarning should be enhanced so that we do not get these silly menus. An exception should work and clients should be able to customise
> it to (for example introduce menu and dialog with the users but they should not be the only default. 
> We see again this plague of interactive environment not being rethought in the 2013 age. 
> 
> defaultAction
> 	
> 	self errorNotification ifFalse: [ ^nil ].
> 	^self openMenuIn: 
> 		[:labels :lines :caption | 
> 		UIManager default chooseFrom: labels lines: lines title: caption]
> 
> but that we could specify the action to be executed instead. 
> 
> 
> to me CompilerException should have nothing to do with UI and popup. Then we should be able to pass objects that knows how to handle
> the errors in interactive way or not. 
> 
> As a clear example, this is just bad that each time we want to change the UI message we have to change the compiler exception. 
> ugly at wish.
> 
> I have no cycle to fix that now. I will check if I can get something in UndefinedObject so that I can continue to work on my task.
> 
> Stef
> 
> 
> 
>> [ OpalCompiler new evaluate: 'AnUnknownClass subclass: #Adaptor1Example
>>         instanceVariableNames: ''customers accountID address name phoneNumber''
>>         classVariableNames: ''''
>>         poolDictionaries: ''''
>>         category: ''Examples-Cookbook''' ] on: OCSemanticWarning do: [ :e | e halt ]
>> 
>> Here we catch the error, and you can handle it. 
>> Now it is not easily possible to resume the error, because you want a global instead and Opal expects a temp (there are way to resume but with very deep stack manipulation that I do not want to show to young pharoers present on this mailing list). So the best is to retry it. One solution is therefore:
>> 
>> [ OpalCompiler new evaluate: 'AnUnknownClass subclass: #Adaptor1Example
>>         instanceVariableNames: ''customers accountID address phoneNumber''
>>         classVariableNames: ''''
>>         poolDictionaries: ''''
>>         category: ''Examples-Cookbook''' ] 
>> on: OCSemanticWarning do: [ :e | 
>> 	Smalltalk at: e node name put: StubRootClass.
>> 	e retry ] 
>> 
>> with e node name answering #AnUnknownClass here.
>> Now you need to make sure that the exception block is executed for the case of a missing superclass and not something else or you will end up creating loads of globals.
>> 
>> The exception block should be something similar to:
>> 
>>  [ :e | 
>>         e node name first isUppercase and: [ "some condition" ] ifTrue: [
>> 	        Smalltalk at: e node name put: StubRootClass.
>> 	        ^ e retry ].
>>         e pass ] 
>> 
>> How to undefined and OCUndeclaredVariableWarning relate?
>> 
>> In your case, while loading from Monticello the code is compiled and evaluated in non interactive mode. Therefore it cannot trigger the default action of OCUndeclaredVariableWarning which is a UI event. So it sets by default the unknown global to:
>> 
>> Undeclared at: varName asSymbol put: nil.
>> OCUndeclaredVariable new name: varName asSymbol
>> 
>> in: OCUndeclaredVariableWarning >>defaultAction
>> 
>> which then later triggers the code in UndefinedObject.
> 
> 
> 

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