[Haskell-cafe] fclabels > 0.5

[Sergey Mironov]

just what I was looking for, thanks!

2012/8/20 Erik Hesselink <hesselink at gmail.com>:
> Untested, but this should be about right:
>
> osi (Bij f b) = iso (Bij b f)
>
> Erik
>
> On Mon, Aug 20, 2012 at 2:35 PM, Sergey Mironov <ierton at gmail.com> wrote:
>> Hi. I'm porting old code, which uses fclabels <0.5. Old fclabels
>> define Iso typeclass as follows:
>>
>> class Iso f where
>>   iso :: a :<->: b -> f a -> f b
>>   iso (Lens a b) = osi (b <-> a)
>>   osi :: a :<->: b -> f b -> f a
>>   osi (Lens a b) = iso (b <-> a)
>>
>> Newer one defines iso:
>>
>> class Iso (~>) f where
>>   iso :: Bijection (~>) a b -> f a ~> f b
>>
>> instance Arrow (~>) => Iso (~>) (Lens (~>) f) where
>>   iso bi = arr ((\a -> lens (fw bi . _get a) (_set a . first (bw bi))) . unLens)
>>
>> instance Arrow (~>) => Iso (~>) (Bijection (~>) a) where
>>   iso = arr . (.)
>>
>> but no osi. I'm not a guru in categories, can you help me define osi?
>>
>> Thanks
>> Sergey.
>>
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