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

Peter Verswyvelen bf3 at telenet.be
Sat Sep 22 06:58:12 EDT 2007


Peter Verswyvelen wrote:

 > http://www.haskell.org/ghc/docs/2.10/users_guide/user_146.html 
<http://www.haskell.org/ghc/docs/2.10/users_guide/user_146.html>seems to 
confirm that?

Oops, sorry, these seems to be docs for Concurrent Haskell... But maybe 
the experts can confirm if the principle still stands?


> I guess you entered a black hole! :-)
>
> The problem is that don't understand black holes myself, I just got 
> introduced with the same thing yesterday :-) I confused me a lot too.
>
> The only explanation I could give you intuitively is that GHCi is 
> running in multi threaded execution mode, and that two or more 
> execution threads are waiting for each other forever, creating a 
> "deadlock".
>
> http://www.haskell.org/ghc/docs/2.10/users_guide/user_146.html 
> <http://www.haskell.org/ghc/docs/2.10/users_guide/user_146.html>seems 
> to confirm that?
>
> If you try the same using (Win)HUGS, you'll get 100% CPU time usage.
>
> Cheers,
> Peter Verswyvelen
>
> Pasqualino 'Titto' Assini wrote:
>> Hi,
>>
>> if I define:
>>
>> f = f
>>
>> and then try to evaluate 'f'  in GHCi, as one would expect, the interpreter 
>> never returns an answer.
>>
>> The funny thing is that, while it is stuck in an infinite loop, GHCi doesn't 
>> seem to use any CPU time at all.
>>
>> How is this possible?
>>
>> Thanks
>>
>>             titto
>>
>>
>>
>>
>>
>>
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