Hi

I'm currently teaching the ObjVlisp reflective kernel and the  
students have to implement it in VW.
Now I realized that I have a bug for the error (equivalent of DNU).  
And I wanted to know
how the squeak VM does it.

My bug is the following one:
	when a message is not understood, the message error is raised. By  
default on Object error raises an Error.

	Now when I redefine the method error on a class, I do not cancel the  
application of the
	method that was not found. So I end up applying (value: self in the  
unarySend: method below)
	the old arguments of the not-found message to the result of the  
redefined error method and this should not 	
	happen.

I have the impression that the solution is to cancel the application  
of the found method when there is an error.
And I wanted to know what the Squeak VM does?

Here how I did it in my ObjVlisp implementation:
Obj is a subclass of Array I use to represent objects and block to  
represent methods

Obj>>lookup: selector for: anObjObject
	
	^(self doesUnderstand: selector)
		ifTrue: [ self bodyOfMethod: selector]
		ifFalse: [self objName = #ObjObject
				ifFalse: [ (Obj giveClassNamed: self objSuperclassId) lookup:  
selector for: anObjObject.]
				ifTrue: [ anObjObject binarySend: #error with: selector
						"this should be escaping the flow"]].

Obj>>unarySend: selector
	| ans |
	"should do something different to deal with the fact that error can  
be redefined"
	ans := (self objClass lookup: selector for: self) value: self.
	^ ans


The method error is defined as follow.
(objectClass at: objectClass offsetForMethodDict) at: #error
		put:
			[:object :selector |
				Transcript show: 'Error: selector ' , selector printString , 'not  
understood';
				cr.
				object error].

So the following code work well when I do not redefine error but not  
when I redefine it.