just what I was looking for, thanks! 2012/8/20 Erik Hesselink :

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 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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