[Haskell-cafe] Lenses that work with Arrows

Tom Ellis tom-lists-haskell-cafe-2013
Mon Oct 7 17:22:33 UTC 2013

On Mon, Oct 07, 2013 at 07:14:44PM +0200, Niklas Haas wrote:
> On Mon, 7 Oct 2013 10:40:13 +0100, Tom Ellis <tom-lists-haskell-cafe-2013 at jaguarpaw.co.uk> wrote:
> > I introduce a very simple extension to the Lens datatype from Control.Lens
> > that allows it to work with Arrows:
> > 
> >     https://gist.github.com/tomjaguarpaw/6865080
> The reason we don't tend to have combinators like ?view? or ?over?
> generalized in their return profunctor like that is because you very
> quickly run into type ambiguity issues.

Perhaps I didn't explain clearly what I am asking for.  The crux of the
issue is whether it is possible *at all* to write the function

    overArr :: Arrow arr => Lens s t a b -> arr a b -> arr s t

not whether it should be merged with over.


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