[Haskell-cafe] Using lenses

[Tony Morris]

Lenses for nested sum types e.g. Either.
 On 03/10/2013 6:08 PM, "Simon Peyton-Jones" <simonpj at microsoft.com> wrote:

>  (I sent this to ?libraries? but Kim-Ee suggested adding Caf?, where so
> many smart people hang out.)****
>
> ** **
>
> Friends****
>
> ** **
>
> Some of you will know that I?ve promised to give a talk about Edward?s
> lens library <http://hackage.haskell.org/package/lens> at the Haskell
> Exchange <http://skillsmatter.com/event/scala/haskell-exchange> in London
> next Wednesday (9th).  I did this to give everyone (including me) a break
> from GHC hackery, and also to force me to learn about this lens voodoo that
> everyone is twittering about.  Edward generously gave me quite a bit of
> one-to-one attention last week (my hair is still standing on end), but this
> message is to ask your help too.****
>
>
> *Specifically, I?d like to give some compelling use-cases*.   If you are
> using the lens library yourself, could you spare a few minutes to tell me
> how you are using it?  I expect to cover Lens and Traversal but not Prism.
> ****
>
> ** **
>
> The use-case everyone starts with is nested records, but I?d like to go
> beyond that.  The next levels seem to be:****
>
> **?         **Lenses as views of data that isn?t ?really there? e.g.
> regarding a record with rectangular coordinates as having polar coordinates
> too.****
>
> **?         **Lenses and Traversals that focus on elements of finite maps
> (Control.Lens.At)****
>
> ** **
>
> What else? I?m sure you are using them in all sorts of cool ways that I
> would never think of, and I?d love to know.****
>
> ** **
>
> Please don?t tell me anything secret!  To give everyone the benefit I may
> just concatenate all the replies and send to you all, so please say if you
> don?t want me to do that with yours. ****
>
> ** **
>
> And don?t burn too many cycles on this...I don?t want to waste your time,
> and I can always get back to you if I can?t understand what you say.
> Sooner is better than later...Weds is coming.****
>
> ** **
>
> Simon ?Edward?s prophet? PJ****
>
> ** **
>
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