On 27 January 2015 at 17:23, Charles Durham
You need to sign up for it, but this is a phenomenal talk by simon peyton jones describing the idea behind lenses the way he understood it.
https://skillsmatter.com/skillscasts/4251-lenses-compositional-data-access-a...
Thanks, I think that was exactly what I needed to know. If I understand the key section right, you can do all that stuff with a straight get/set pair but it'd be desperately inefficient, so then you add an update function, and then one at Maybe and [] and IO and they all start to look the same so you generalise to all Functors, and then you discover that using Const you get a getter, and Identity gives you a setter, so you can throw them away and end up with a lens as we know it. And then you generalise it in about a billion other directions and you end up with the lens library! Much obliged, David