[Swift-devel] Problem with iterate

[Ioan Raicu]

Mihael Hategan wrote:
> On Fri, 2010-02-19 at 10:59 -0600, Ioan Raicu wrote:
>   
>> But lets bring this back to a more real example. A user wanting to
>> express some computations that have some dependencies, would write out
>> their computations in some order, expecting their order to be
>> preserved because of the dependencies. If you only support single
>> assignment on variables (e.g. the data), then an example like the one
>> below could never deadlock because the single assignment would be
>> violated on the 2nd statement. Perhaps things are more complicated if
>> you support multiple assignments per variables, but that is not the
>> case for Swift, right? 
>>     
>
> x = y + 1
> y = x + 1
>
> How many assignments are there? 2
> How many variables are being assigned? 2
> Do those assignments have the same lvalue (thing on the left)? no
> ---
> Conclusion: each variable is assigned exactly once.
>   
However, y and x have to be defined somewhere, right? If they don't get 
their value assigned at definition time, then the statement x = y + 1 
should return with an error that y is not defined.
>   
>> I am trying to understand if this deadlock is happening in Swift due
>> to some particular implementation detail in Swift (or underlying
>> pieces), or is it a fundamental flaw in the DAG based approach with
>> single assignment variables? Or is it due to something completely
>> different?
>>     
>
> It seems to be a fundamental flaw with computers and algorithms.
>   

-- 
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Ioan Raicu, Ph.D.
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