[Haskell-cafe] Re: Wikipedia on first-class object

[apfelmus]

Achim Schneider wrote:
> Jonathan Cast wrote:
>> More importantly, we can prove that [1..] == [1..] = _|_, since
>>
>>    [1..] == [1..]
>> = LUB (n >= 1) [1..n] ++ _|_ == [1..n] ++ _|_
>> = LUB (n >= 1) _|_
>> = _|_
>>
> As far as I understand
> http://www.haskell.org/haskellwiki/Bottom
> , only computations which cannot be successful are bottom, not those
> that can be successful, but aren't. Kind of idealizing reality, that is.

Ah, that's only a glitch in the wording. [1..] == [1..] is still _|_ 
since it loops forever.

For more about _|_, see also

   http://en.wikibooks.org/wiki/Haskell/Denotational_semantics


Regards,
apfelmus