[Haskell-cafe] Lenses that work with Arrows

[Tom Ellis]

On Mon, Oct 07, 2013 at 06:22:33PM +0100, Tom Ellis wrote:
> 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.

Edward Kmett has answered in the affirmative, which pleases me greatly!

    http://www.reddit.com/r/haskell/comments/1nwetz/lenses_that_work_with_arrows/ccmtfkj