[Haskell-cafe] what is f=f (not) doing ?

[Bulat Ziganshin]

Hello Lennart,

Sunday, September 23, 2007, 8:30:43 PM, you wrote:

and GHC stops executing this thread - wise solution. but it can't
decide whether some signal handlers/backcalls are established and so
whther are program definitely will never finish or not

> But this was a very particular case when a thread starts evaluating
> a node and then comes back to the same node again.
> The general case is (of course) undecidable.

> On 9/23/07,  Bulat Ziganshin <bulat.ziganshin at gmail.com> wrote:
>  Hello Lennart,

> Sunday, September 23, 2007, 2:05:46 PM, you wrote:

> i bet that general case contains too much conditions to check. program
> may be unblocked by other thread, by OS signal, by I/O operation
>  completion, by C thread. how for example RTS can check that we have
> started I/O operation with completion callback which will call abort()
> function?

>> I agree. This situation is totally detectable.

 >> On 9/23/07, Neil Mitchell <ndmitchell at gmail.com> wrote:
>> Hi

>>> I'm not sure, but since it would require the detection of an evaluation
 >>> that does not terminate,it comes down to the halting problem, which is 
>>> not generally solvable. Maybe the experts can confirm my intuition?

>> I think your intuition is off. This isn't the problem of detecting
>> that a computation might not halt, its a question of detecting after 
>> the fact a very restricted case of non-termination has occurred. I
>> think it should be possible to assign threads etc to these things, but
>> may make the code run slower in the common case.

>> Thanks 

>> Neil
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>  Bulat                            mailto:Bulat.Ziganshin at gmail.com
>  
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Best regards,
 Bulat                            mailto:Bulat.Ziganshin at gmail.com