1) #xor: should not take a block as argument.
Rationale:
- the block would ALWAYS have to be evaluated
- block arguments are either for repeated evaluation, or condiitonal
evaluation...
This is not the case here, so the need of a block argument vanishes...

2) #xor: argument should be a Boolean, but here no guard is made.

We could eventually add:
   aBoolean isBoolean ifFalse; [self error: 'xor must take a boolean as
argument']

Or if we want to later extend to some other class:
True>>xor: aBoolean
    ^aBoolean xorTrue
False>>xor: aBoolean
    ^aBoolean xorFalse
True>>xorTrue
    ^false
True>>xorFalse
    ^self
False>>xorTrue
    ^true
False>>xorFalse
    ^self

MySymbolicBooleanClass>>xorTrue
    ^SymbolicXorOperation with: self with: true

I'm not sure whether we need to protect or not...
I tend to avoid over-protecting code. As long as a debugger opens, I claim
protecting is void...
But here, I don't like a false program proceeding without a Notifier....

Nicolas

2009/3/24 Keith Hodges <keith_hodges at yahoo.co.uk>

> true xor: [ true ]  => true
>
> discuss
>
> Keith
>
>
>
>
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