[Haskell-cafe] Fixed points

[Alexander Solla]

On Fri, Jun 10, 2011 at 12:05 PM, Alexander Solla <alex.solla at gmail.com>wrote:

> On Thu, Jun 9, 2011 at 6:04 PM, Felipe Almeida Lessa <
> felipe.lessa at gmail.com> wrote:
>
>> Something like this?
>>
>>  equivalenceClosure = fix $ \f e ->
>>    let e' = reflexivity . symmetry . transitivity $ e
>>    in if e' == e then e else f e'
>>
>> Cheers,
>>
>> --
>> Felipe.
>>
>
> I managed something even "clearer".  I still have very little intuition
> about what's going on, but I had an aha moment -- which I promptly forgot
> :0( -- and at least there's a mechanical translation from the iterate
> version to the fix one.
>
> equivalenceClosure :: (Ord a) => Relation a -> Relation a
> equivalenceClosure = fix (\f -> reflexivity . symmetry . transitivity)
>

Cancel that, it's not passing my tests.
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