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:

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On Mon, 7 Oct 2013 10:40:13 +0100, Tom Ellis wrote:

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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...